Upgrading from 1.x

Modern Fabric (2+) represents a near-total reimplementation & reorganization of the software. It’s been broken in two, cleaned up, made more explicit, and so forth. In some cases, upgrading requires only basic search & replace; in others, more work is needed.

If you read this document carefully, it should guide you in the right direction until you’re fully upgraded. If any functionality you’re using in Fabric 1 isn’t listed here, please file a ticket on Github and we’ll update it ASAP.

Warning

As of the 2.0 release line, Fabric 2 is not at 100% feature parity with 1.x! Some features have been explicitly dropped, but others simply have not been ported over yet, either due to time constraints or because said features need to be re-examined in a modern context.

Please review the information below, including the Upgrade specifics section which contains a very detailed list, before filing bug reports!

Also see the roadmap for additional notes about release versioning.

Why upgrade?

We’d like to call out, in no particular order, some specific improvements in modern Fabric that might make upgrading worth your time.

Note

These are all listed in the rest of the doc too, so if you’re already sold, just skip there.

  • Python 3 compatibility (specifically, we now support 2.7 and 3.4+);
  • Thread-safe - no more requirement on multiprocessing for concurrency;
  • API reorganized around fabric.connection.Connection objects instead of global module state;
  • Command-line parser overhauled to allow for regular GNU/POSIX style flags and options on a per-task basis (no more fab mytask:weird=custom,arg=format);
  • Task organization is more explicit and flexible / has less ‘magic’;
  • Tasks can declare other tasks to always be run before or after themselves;
  • Configuration massively expanded to allow for multiple config files & formats, env vars, per-user/project/module configs, and much more;
  • SSH config file loading enabled by default & has been fleshed out re: system/user/runtime file selection;
  • Shell command execution API consistent across local and remote method calls - no more differentiation between local and run (besides where the command runs, of course!);
  • Shell commands significantly more flexible re: interactive behavior, simultaneous capture & display (now applies to local subprocesses, not just remote), encoding control, and auto-responding;
  • Use of Paramiko’s APIs for the SSH layer much more transparent - e.g. fabric.connection.Connection allows control over the kwargs given to SSHClient.connect;
  • Gateway/jump-host functionality offers a ProxyJump style ‘native’ (no proxy-command subprocesses) option, which can be nested infinitely;

‘Sidegrading’ to Invoke

We linked to a note about this above, but to be explicit: modern Fabric is really a few separate libraries, and anything not strictly SSH or network related has been split out into the Invoke project.

This means that if you’re in the group of users leveraging Fabric solely for its task execution or local, and never used run, put or similar - you don’t need to use Fabric itself anymore and can simply ‘sidegrade’ to Invoke instead.

You’ll still want to read over this document to get a sense of how things have changed, but be aware that you can get away with pip install invoke and won’t need Fabric, Paramiko, cryptography dependencies, or anything else.

Using modern Fabric from within Invoke

We intend to enhance modern Fabric until it encompasses the bulk of Fabric 1’s use cases, such that you can use fab and fabfiles on their own without caring too much about how it’s built on top of Invoke.

However, prior to that point – and very useful on its own for intermediate-to-advanced users – is the fact that modern Fabric is designed with library or direct API use in mind. It’s entirely possible, and in some cases preferable, to use Invoke for your CLI needs and Fabric as a pure API within your Invoke tasks.

In other words, you can eschew fab/fabfiles entirely unless you find yourself strongly needing the conveniences it wraps around ad-hoc sessions, such as --hosts and the like.

Running both Fabric versions simultaneously

To help with gradual upgrades, modern Fabric may be installed under the name fabric2 (in addition to being made available “normally” as versions 2.0+ of fabric) and can live alongside installations of version 1.x.

Thus, if you have a large codebase and don’t want to make the jump to modern versions in one leap, it’s possible to have both Fabric 1 (fabric, as you presumably had it installed previously) and modern Fabric (as fabric2) resident in your Python environment simultaneously.

Note

We strongly recommend that you eventually migrate all code using Fabric 1, to versions 2 or above, so that you can move back to installing and importing under the fabric name. fabric2 as a distinct package and module is intended to be a stopgap, and there will not be any fabric3 or above (not least because some of those names are already taken!)

For details on how to obtain the fabric2 version of the package, see Installing modern Fabric as fabric2.

Creating Connection and/or Config objects from v1 settings

A common tactic when upgrading piecemeal is to generate modern Fabric objects whose contents match the current Fabric 1 environment. Whereas Fabric 1 stores all configuration (including the “current host”) in a single place – the env object – modern Fabric breaks things up into multiple (albeit composed) objects: Connection for per-connection parameters, and Config for general settings and defaults.

In most cases, you’ll only need to generate a Connection object using the alternate class constructor Connection.from_v1, which should be fed your appropriate local fabric.api.env object; see its API docs for details.

A contrived example:

from fabric.api import env, run
from fabric2 import Connection

env.host_string = "[email protected]"
run("whoami") # v1
cxn = Connection.from_v1(env)
cxn.run("whoami") # v2+

By default, this constructor calls another API member – Config.from_v1 – internally on your behalf. Users who need tighter control over modern-style config options may opt to call that classmethod explicitly and hand their modified result into Connection.from_v1, which will cause the latter to skip any implicit config creation.

Mapping of v1 env vars to modern API members

The env vars and how they map to Connection arguments or Config values (when fed into the .from_v1 constructors described above) are listed below.

v1 env var v2+ usage (prefixed with the class it ends up in)
always_use_pty Config: run.pty.
forward_agent Config: connect_kwargs.forward_agent.
gateway Config: gateway.
host_string Connection: host kwarg (which can handle host-string like values, including user/port).
key

Not supported: Fabric 1 performed extra processing on this (trying a bunch of key classes to instantiate) before handing it into Paramiko; modern Fabric prefers to just let you handle Paramiko-level parameters directly.

If you’re filling your Fabric 1 key data from a file, we recommend switching to key_filename instead, which is supported.

If you’re loading key data from some other source as a string, you should know what type of key your data is and manually instantiate it instead, then supply it to the connect_kwargs parameter. For example:

from io import StringIO  # or 'from StringIO' on Python 2
from fabric.state import env
from fabric2 import Connection
from paramiko import RSAKey
from somewhere import load_my_key_string

pkey = RSAKey.from_private_key(StringIO(load_my_key_string()))
cxn = Connection.from_v1(env, connect_kwargs={"pkey": pkey})
key_filename Config: connect_kwargs.key_filename.
no_agent Config: connect_kwargs.allow_agent (inverted).
password Config: connect_kwargs.password, as well as sudo.password if and only if the env’s sudo_password (see below) is unset. (This mimics how v1 uses this particular setting - in earlier versions there was no sudo_password at all.)
port

Connection: port kwarg. Is casted to an integer due to Fabric 1’s default being a string value (which is not valid in v2).

Note

Since v1’s port is used both for a default and to store the current connection state, v2 uses it to fill in the Connection only, and not the Config, on assumption that it will typically be the current connection state.

ssh_config_path Config: ssh_config_path.
sudo_password Config: sudo.password.
sudo_prompt Config: sudo.prompt.
timeout Config: timeouts.connection (because v1’s ambiguously named timeout setting was, in fact, for connection timeouts).
use_ssh_config Config: load_ssh_configs.
user Connection: user kwarg.
warn_only Config: run.warn

Upgrade specifics

This is (intended to be) an exhaustive list of all Fabric 1.x functionality, as well as new-to-Invoke-or-Fabric-2 functionality not present in 1.x; it specifies whether upgrading is necessary, how to upgrade if so, and tracks features which haven’t been implemented in modern versions yet.

Most sections are broken down in table form, as follows:

Fabric 1 feature or behavior Status, see below for breakdown Migration notes, removal rationale, etc

Below are the typical values for the ‘status’ column, though some of them are a bit loose - make sure to read the notes column in all cases! Also note that things are not ironclad - eg any ‘removed’ item has some chance of returning if enough users request it or use cases are made that workarounds are insufficient.

  • Ported: available already, possibly renamed or moved (frequently, moved into the Invoke codebase.)
  • Pending: would fit, but has not yet been ported, good candidate for a patch. These entries link to the appropriate Github ticket - please do not make new ones!
  • Removed: explicitly not ported (no longer fits with vision, had too poor a maintenance-to-value ratio, etc) and unlikely to be reinstated.

Here’s a quick local table of contents for navigation purposes:

General / conceptual

  • Modern Fabric is fully Python 3 compatible; as a cost, Python 2.5 support (a longstanding feature of Fabric 1) has been dropped - in fact, we’ve dropped support for anything older than Python 2.7.

  • The CLI task-oriented workflow remains a primary design goal, but the library use case is no longer a second-class citizen; instead, the library functionality has been designed first, with the CLI/task features built on top of it.

  • Additionally, within the CLI use case, version 1 placed too much emphasis on ‘lazy’ interactive prompts for authentication secrets or even connection parameters, driven in part by a lack of strong configuration mechanisms. Over time it became clear this wasn’t worth the tradeoffs of having confusing noninteractive behavior and difficult debugging/testing procedures.

    Modern Fabric takes an arguably cleaner approach (based on functionality added to v1 over time) where users are encouraged to leverage the configuration system and/or serve the user prompts for runtime secrets at the start of the process; if the system determines it’s missing information partway through, it raises exceptions instead of prompting.

  • Invoke’s design includes explicit user-facing testing functionality; if you didn’t find a way to write tests for your Fabric-using code before, it should be much easier now.

    • We recommend trying to write tests early on; they will help clarify the upgrade process for you & also make the process safer!

API organization

High level code flow and API member concerns.

Import everything via fabric.api Removed All useful imports are now available at the top level, e.g. from fabric import Connection.
Configure connection parameters globally (via env.host_string, env.host, env.port, env.user) and call global methods which implicitly reference them (run/sudo/etc) Removed

The primary API is now properly OOP: instantiate fabric.connection.Connection objects and call their methods. These objects encapsulate all connection state (user, host, gateway, etc) and have their own SSH client instances.

Emphasis on serialized “host strings” as method of setting user, host, port, etc Ported/Removed

fabric.connection.Connection can accept a shorthand “host string”-like argument, but the primary API is now explicit user, host, port, etc keyword arguments.

Additionally, many arguments/settings/etc that expected a host string in v1 will now expect a fabric.connection.Connection instance instead.

Use of “roles” as global named lists of host strings Ported

This need is now served by fabric.group.Group objects (which wrap some number of fabric.connection.Connection instances with “do a thing to all members” methods.) Users can create & organize these any way they want.

See the line items for --roles (CLI arguments, options and behavior), env.roles (fabric.env reference) and @roles (Task functions & decorators) for the status of those specifics.

Task functions & decorators

Note

Nearly all task-related functionality is implemented in Invoke; for more details see its execution and namespaces documentation.

By default, tasks are loaded from a fabfile.py which is sought up towards filesystem root from the user’s current working directory Ported This behavior is basically identical today, with minor modifications and enhancements (such as tighter control over the load process, and API hooks for implementing custom loader logic - see Loading collections.)
“Classic” style implicit task functions lacking a @task decorator Removed These were on the way out even in v1, and arbitrary task/namespace creation is more explicitly documented now, via Invoke’s Task and Collection.
“New” style @task-decorated, module-level task functions Ported Largely the same, though now with superpowers - @task can still be used without any parentheses, but where v1 only had a single task_class argument, the new version (largely based on Invoke’s) has a number of namespace and parser hints, as well as execution related options (such as those formerly served by @hosts and friends).
Arbitrary task function arguments (i.e. def mytask(any, thing, at, all)) Ported

This gets its own line item because: tasks must now take a Context (vanilla Invoke) or fabric.connection.Connection (Fabric) object as their first positional argument. The rest of the function signature is, as before, totally up to the user & will get automatically turned into CLI flags.

This sacrifices a small bit of the “quick DSL” of v1 in exchange for a cleaner, easier to understand/debug, and more user-overrideable API structure.

As a side effect, it lessens the distinction between “module of functions” and “class of methods”; users can more easily start with the former and migrate to the latter when their needs grow/change.

Implicit task tree generation via import-crawling Ported/Removed

Namespace construction is now more explicit; for example, imported modules in your fabfile.py are no longer auto-scanned and auto-added to the task tree.

However, the root fabfile.py is automatically loaded (using Collection.from_module), preserving the simple/common case. See Constructing namespaces for details.

We may reinstate (in an opt-in fashion) imported module scanning later, since the use of explicit namespace objects still allows users control over the tree that results.

@hosts for determining the default host or list of hosts a given task uses Ported Reinstated as the hosts parameter of @task. Further, it can now handle dicts of fabric.connection.Connection kwargs in addition to simple host strings.
@roles for determining the default list of group-of-host targets a given task uses Pending See API organization for details on the overall ‘roles’ concept. When it returns, this will probably follow @hosts and become some @task argument.
@serial/@parallel/@runs_once Ported/Pending

Parallel execution is currently offered at the API level via fabric.group.Group subclasses such as fabric.group.ThreadingGroup; however, designating entire sessions and/or tasks to run in parallel (or to exempt from parallelism) has not been solved yet.

The problem needs solving at a higher level than just SSH targets, so this links to an Invoke-level ticket.

execute for calling named tasks from other tasks while honoring decorators and other execution mechanics (as opposed to calling them simply as functions) Pending This is one of the top “missing features” from the rewrite; link is to Invoke’s tracker.
Task class for programmatic creation of tasks (as opposed to using some function object and the @task decorator) Ported While not sharing many implementation details with v1, modern Fabric (via Invoke) has a publicly exposed Task class, which alongside Collection allow full programmatic creation of task trees, no decorator needed.

CLI arguments, options and behavior

Exposure of task arguments as custom colon/comma delimited CLI arguments, e.g. fab mytask:posarg,kwarg=val Removed CLI arguments are now proper GNU/POSIX-style long and short flags, including globbing shortflags together, space or equals signs to attach values, optional values, and much more. See Invoking tasks.
Task definition names are mirrored directly on the command-line, e.g for task def journald_logs(), command line argument is fab journald_logs Removed Tasks names now get converted from underscores to hyphens. Eg. task def journald_logs() now evaluates to fab journald-logs on the commandline.
Ability to invoke multiple tasks in a single command line, e.g. fab task1 task2 Ported Works great!
python -m fabric as stand-in for fab Ported Ported in 2.2.
-a/--no_agent for disabling automatic SSH agent key selection Removed To disable use of an agent permanently, set config value connect_kwargs.allow_agent to False; to disable temporarily, unset the SSH_AUTH_SOCK env var.
-A/--forward-agent for enabling agent forwarding to the remote end Removed The config and kwarg versions of this are ported, but there is currently no CLI flag. Usual “you can set the config value at runtime with a shell env variable” clause is in effect, so this may not get ported, depending.
--abort-on-prompts to turn interactive prompts into exceptions (helps avoid ‘hanging’ sessions) Removed See the notes about interactive prompts going away in General / conceptual. Without mid-session prompts, there’s no need for this option.
-c/--config for specifying an alternate config file path Ported --config lives on, but the short flag is now -f (-c now determines which collection module name is sought by the task loader.)
--colorize-errors (and env.colorize_errors) to enable ANSI coloring of error output Pending Very little color work has been done yet and this is one of the potentially missing pieces. We’re unsure how often this was used in v1 so it’s possible it won’t show up again, but generally, we like using color as an additional output vector, so…
-d/--display for showing info on a given command Ported This is now the more standard -h/--help, and can be given in either “direction”: fab -h mytask or fab mytask -h.
-D/--disable-known-hosts to turn off Paramiko’s automatic loading of user-level known_hosts files Pending Not ported yet, probably will be.
-e/--eagerly-disconnect (and env.eagerly_disconnect) which tells the execution system to disconnect from hosts as soon as a task is done running Ported/Pending There’s no explicit connection cache anymore, so eager disconnection should be less necessary. However, investigation and potential feature toggles are still pending.
-f/--fabfile to select alternate fabfile location Ported This is now split up into -c/--collection and -r/--search-root; see Loading collections.
-g/--gateway (and env.gateway) for selecting a global SSH gateway host string Pending

One can set the global gateway config option via an environment variable, which at a glance would remove the need for a dedicated CLI option. However, this approach only allows setting string values, which in turn only get used for ProxyCommand style gatewaying, so it doesn’t replace v1’s --gateway (which took a host string and turned it into a ProxyJump style gateway).

Thus, if enough users notice the lack, we’ll consider a feature-add that largely mimics the v1 behavior: string becomes first argument to fabric.connection.Connection and that resulting object is then set as gateway.

--gss-auth/--gss-deleg/--gss-kex Removed These didn’t seem used enough to be worth porting over, especially since they fall under the usual umbrella of “Paramiko-level connect passthrough” covered by the connect_kwargs config option. (Which, if necessary, can be set at runtime via shell environment variables, like any other config value.)
--hide/--show for tweaking output display globally Removed This is configurable via the config system and env vars.
-H/--hosts Ported Works basically the same as before - if given, is shorthand for executing any given tasks once per host.
-i for SSH key filename selection Ported Works same as v1, including ability to give multiple times to build a list of keys to try.
-I/--initial-password-prompt for requesting an initial pre-execution password prompt Ported It’s now --prompt-for-login-password, –prompt-for-sudo-password or --prompt-for-passphrase, depending on whether you were using the former to fill in passwords or key passphrases (or both.)
--initial-sudo-password-prompt for requesting an initial pre-execution sudo password prompt Ported This is now --prompt-for-sudo-password. Still a bit of a mouthful but still 4 characters shorter!
-k/--no-keys which prevents Paramiko’s automatic loading of key files such as ~/.ssh/id_rsa Removed Use environment variables to set the connect_kwargs.look_for_keys config value to False.
--keepalive for setting network keepalive Pending Not ported yet.
-l/--list for listing tasks, plus -F/--list-format for tweaking list display format Ported Now with bonus JSON list-format! Which incidentally replaces -F short/--shortlist.
--linewise for buffering output line by line instead of roughly byte by byte Removed This doesn’t really fit with the way modern command execution code views the world, so it’s gone.
-n/--connection-attempts controlling multiple connect retries Pending Not ported yet.
--no-pty to disable automatic PTY allocation in run, etc Ported Is now -p/--pty as the default behavior was switched around.
--password/--sudo-password for specifying login/sudo password values Removed This is typically not very secure to begin with, and there are now many other avenues for setting the related configuration values, so they’re gone at least for now.
-P/--parallel for activating global parallelism Pending See the notes around @parallel in Task functions & decorators.
--port to set default SSH port Removed Our gut says this is best left up to the configuration system’s env var layer, or use of the port kwarg on fabric.connection.Connection; however it may find its way back.
r/--reject-unknown-hosts to modify Paramiko known host behavior Pending Not ported yet.
-R/--roles for global list-of-hosts target selection Pending As noted under API organization, role lists are only partially applicable to the new API and we’re still feeling out whether/how they would work at a global or CLI level.
--set key=value for setting fabric.state.env vars at runtime Removed This is largely obviated by the new support for shell environment variables (just do INVOKE_KEY=value fab mytask or similar), though it’s remotely possible a CLI flag method of setting config values will reappear later.
-s/--shell to override default shell path Removed Use the configuration system for this.
--shortlist for short/computer-friendly list output Ported See --list/--list-format - there’s now a JSON format instead. No point reinventing the wheel.
--skip-bad-hosts (and env.skip_bad_hosts) to bypass problematic hosts Pending Not ported yet.
--skip-unknown-tasks and env.skip_unknown_tasks for silently skipping past bogus task names on CLI invocation Removed This felt mostly like bloat to us and could require nontrivial parser changes to reimplement, so it’s out for now.
--ssh-config-path and env.ssh_config_path for selecting an SSH config file Ported This is now -S/--ssh-config.
--system-known-hosts to trigger loading systemwide known_hosts files Pending/Removed This isn’t super likely to come back as its own CLI flag but it may well return as a configuration value.
-t/--timeout controlling connection timeout Ported This is now part of the direct passthrough to Paramiko-level connection parameters, the connect_kwargs config value.
-T/--command-timeout Pending See notes in Shell command execution (local/run/sudo) around the timeout kwarg.
-u/--user to set global default username Removed Most of the time, configuration (env vars for true runtime, or eg user/project level config files as appropriate) should be used for this, but it may return.
-w/--warn-only to toggle warn-vs-abort behavior Ported Ported as-is, no changes.
-x/--exclude-hosts (and env.exclude_hosts) for excluding otherwise selected targets Pending Not ported yet, is pending an in depth rework of global (vs hand-instantiated) connection/group selection.
-z/--pool-size for setting parallel-mode job queue pool size Removed There’s no job queue anymore, or at least at present. Whatever replaces it (besides the already-implemented threading model) is likely to look pretty different.

Shell command execution (local/run/sudo)

General

Behaviors shared across either run/sudo, or all of run/sudo/local. Subsequent sections go into per-function differences.

local and run/sudo have wildly differing APIs and implementations Removed

All command execution is now unified; all three functions (now methods on fabric.connection.Connection, though local is also available as invoke.run for standalone use) have the same underlying protocol and logic (the Runner class hierarchy), with only low-level details like process creation and pipe consumption differing.

For example, in v1 local required you to choose between displaying and capturing subprocess output; modern local is like run and does both at the same time.

Prompt auto-response, via env.prompts and/or sudo’s internals Ported

The env.prompts functionality has been significantly fleshed out, into a framework of Watchers which operate on any (local or remote!) running command’s input and output streams.

In addition, sudo has been rewritten to use that framework; while still useful enough to offer an implementation in core, it no longer does anything users cannot do themselves using public APIs.

fabric.context_managers.cd/lcd (and prefix) allow scoped mutation of executed comments Ported/Pending These are now methods on Context (Context.cd, Context.prefix) but need work in its subclass fabric.connection.Connection (quite possibly including recreating lcd) so that local vs remote state are separated.
fabric.context_managers.shell_env and its specific expression path (plus env.shell_env, env.path and env.path_behavior), for modifying remote environment variables (locally, one would just modify os.environ.) Ported The context managers were the only way to set environment variables at any scope; in modern Fabric, subprocess shell environment is controllable per-call (directly in fabric.connection.Connection.run and siblings via an env kwarg) and across multiple calls (by manipulating the configuration system, statically or at runtime.)
Controlling subprocess output & other activity display text by manipulating fabric.state.output (directly or via fabric.context_managers.hide, show or quiet as well as the quiet kwarg to run/sudo; plus utils.puts/fastprint) Ported/Pending

The core concept of “output levels” is gone, likely to be replaced in the near term by a logging module (stdlib or other) which output levels poorly reimplemented.

Command execution methods like run retain a hide kwarg controlling which subprocess streams are copied to your terminal, and an echo kwarg controlling whether commands are printed before execution. All of these also honor the configuration system.

timeout kwarg and the CommandTimeout exception raised when said command-runtime timeout was violated Pending Command timeouts have not been ported yet, but will likely be added (at the Invoke layer) in future.
pty kwarg and env.always_use_pty, controlling whether commands run in a pseudo-terminal or are invoked directly Ported

This has been thoroughly ported (and its behavior often improved) including preservation of the pty kwarg and updating the config value to be simply run.pty. However, a major change is that pty allocation is now False by default instead of True.

Fabric 0.x and 1.x already changed this value around; during Fabric 1’s long lifetime it became clear that neither default works for all or even most users, so we opted to return the default to False as it’s cleaner and less wasteful.

combine_stderr (kwarg and env.combine_stderr) controlling whether Paramiko weaves remote stdout and stderr into the stdout stream Removed

This wasn’t terrifically useful, and often caused conceptual problems in tandem with pty (as pseudo-terminals by their nature always combine the two streams.)

We recommend users who really need both streams to be merged, either use shell redirection in their command, or set pty=True.

warn_only kwarg for preventing automatic abort on non-zero return codes Ported This is now just warn, both kwarg and config value. It continues to default to False.
stdout and stderr kwargs for reassigning default stdout/err mirroring targets, which otherwise default to the appropriate sys members Ported These are now out_stream and err_stream but otherwise remain similar in nature. They are also accompanied by the new, rather obvious in hindsight in_stream.
capture_buffer_size arg & use of a ring buffer for storing captured stdout/stderr to limit total size Pending Existing Runner implementation uses regular lists for capture buffers, but we fully expect to upgrade this to a ring buffer or similar at some point.
Return values are string-like objects with extra attributes like succeeded and return_code sprinkled on top Ported

Return values are no longer string-a-likes with a semi-private API, but are full fledged regular objects of type Result. They expose all of the same info as the old “attribute strings”, and only really differ in that they don’t pretend to be strings themselves.

They do, however, still behave as booleans - just ones reflecting the exit code’s relation to zero instead of whether there was any stdout.

open_shell for obtaining interactive-friendly remote shell sessions (something that run historically was bad at ) Ported Technically “removed”, but only because the new version of run is vastly improved and can deal with interactive sessions at least as well as the old open_shell did, if not moreso. c.run("/my/favorite/shell", pty=True) should be all you need.

run

shell / env.use_shell designating whether or not to wrap commands within an explicit call to e.g. /bin/sh -c "real command"; plus their attendant options like shell_escape Removed

Non-sudo remote execution never truly required an explicit shell wrapper: the remote SSH daemon hands your command string off to the connecting user’s login shell in almost all cases. Since wrapping is otherwise extremely error-prone and requires frustrating escaping rules, we dropped it for this use case.

See the matching line items for local and sudo as their situations differ. (For now, because they all share the same underpinnings, fabric.connection.Connection.run does accept a shell kwarg - it just doesn’t do anything with it.)

sudo

Unless otherwise noted, all common run``+``sudo args/functionality (e.g. pty, warn_only etc) are covered above in the section on run; the below are sudo specific.

shell / env.use_shell designating whether or not to wrap commands within an explicit call to e.g. /bin/sh -c "real command" Pending/Removed

See the note above under run for details on shell wrapping as a general strategy; unfortunately for sudo, some sort of manual wrapping is still necessary for nontrivial commands (i.e. anything using actual shell syntax as opposed to a single program’s argv) due to how the command string is handed off to the sudo program.

We hope to upgrade sudo soon so it can perform a common-best-case, no-escaping-required shell wrapping on your behalf; see the ‘Pending’ link.

user argument (and env.sudo_user) allowing invocation via sudo -u <user> (instead of defaulting to root) Ported This is still here, and still called user.
group argument controlling the effective group of the sudo’d command Pending This has not been ported yet.

local

See the ‘general’ notes at top of this section for most details about the new local. A few specific extras are below.

shell kwarg designating which shell to ask subprocess.Popen to use Ported Basically the same as in v1, though there are now situations where os.execve (or similar) is used instead of subprocess.Popen. Behavior is much the same: no shell wrapping (as in legacy run), just informing the operating system what actual program to run.

Utilities

Error handling via abort and warn Ported

The old functionality leaned too far in the “everything is a DSL” direction & didn’t offer enough value to offset how it gets in the way of experienced Pythonistas.

These functions have been removed in favor of “just raise an exception” (with one useful option being Invoke’s Exit) as exception handling feels more Pythonic than thin wrappers around sys.exit or having to except SystemExit: and hope it was a SystemExit your own code raised!

ANSI color helpers in fabric.colors allowed users to easily print ANSI colored text without a standalone library Removed

There seemed no point to poorly replicating one of the many fine terminal-massaging libraries out there (such as those listed in the description of #101) in the rewrite, so we didn’t.

That said, it seems highly plausible we’ll end up vendoring such a library in the future to offer internal color support, at which point “baked-in” color helpers would again be within easy reach.

with char_buffered context manager for forcing a local stream to be character buffered Ported This is now character_buffered.
docs.unwrap_tasks for extracting docstrings from wrapped task functions Ported v1 required using a Fabric-specific ‘unwrap_tasks’ helper function somewhere in your Sphinx build pipeline; now you can instead just enable the new invocations.autodoc Sphinx mini-plugin in your extensions list; see link for details.
network.normalize, denormalize and parse_host_string, ostensibly internals but sometimes exposed to users for dealing with host strings Removed As with other host-string-related tools, these are gone and serve no purpose. fabric.connection.Connection is now the primary API focus and has individual attributes for all “host string” components.
utils.indent for indenting/wrapping text (uncommonly used) Pending Not ported yet; ideally we’ll just vendor a third party lib in Invoke.
reboot for rebooting and reconnecting to a remote system Removed

No equivalent has been written for modern Fabric; now that the connection/client objects are made explicit, one can simply instantiate a new object with the same parameters (potentially with sufficient timeout parameters to get past the reboot, if one doesn’t want to manually call something like time.sleep.)

There is a small chance it will return if there appears to be enough need; if so, it’s likely to be a more generic reconnection related fabric.connection.Connection method, where the user is responsible for issuing the restart shell command via sudo themselves.

require for ensuring certain key(s) in env have values set, optionally by noting they can be provided_by= a list of setup tasks Removed This has not been ported, in part because the maintainers never used it themselves, and is unlikely to be directly reimplemented. However, its core use case of “require certain data to be available to run a given task” may return within the upcoming dependency framework.
prompt for prompting the user & storing the entered data (optionally with validation) directly into env Removed Like require, this seemed like a less-used feature (especially compared to its sibling confirm) and was not ported. If it returns it’s likely to be via invocations, which is where confirm ended up.

Networking

env.gateway for setting an SSH jump gateway Ported

This is now the gateway kwarg to fabric.connection.Connection, and – for the newly supported ProxyJump style gateways, which can be nested indefinitely! – should be another fabric.connection.Connection object instead of a host string.

(You may specify a runtime, non-SSH-config-driven ProxyCommand-style string as the gateway kwarg instead, which will act just like a regular ProxyCommand.)

ssh_config-driven ProxyCommand support Ported This continues to work as it did in v1.
with remote_tunnel(...): port forwarding Ported This is now fabric.connection.Connection.forward_local, since it’s used to forward a local port to the remote end. (Newly added is the logical inverse, fabric.connection.Connection.forward_remote.)
NetworkError raised on some network related errors Removed In v1 this was simply a (partially implemented) stepping-back from the original “just sys.exit on any error!” behavior. Modern Fabric is significantly more exception-friendly; situations that would raise NetworkError in v1 now simply become the real underlying exceptions, typically from Paramiko or the stdlib.
env.keepalive for setting network keepalive value Pending Not ported yet.
env.connection_attempts for setting connection retries Pending Not ported yet.
env.timeout for controlling connection timeout Ported This is now controllable both via the configuration system and a direct kwarg on fabric.connection.Connection.

Authentication

Note

Some env keys from v1 were simply passthroughs to Paramiko’s SSHClient.connect method. Modern Fabric gives you explicit control over the arguments it passes to that method, via the connect_kwargs configuration subtree, and the below table will frequently refer you to that approach.

env.key_filename Ported Use connect_kwargs.
env.password Ported

Use connect_kwargs.

Also note that this used to perform double duty as connection and sudo password; the latter is now found in the sudo.password setting.

env.gss_(auth|deleg|kex) Ported Use connect_kwargs.
env.key, a string or file object holding private key data, whose specific type is auto-determined and instantiated for use as the pkey connect kwarg Removed This has been dropped as unnecessary (& bug-prone) obfuscation of Paramiko-level APIs; users should already know which type of key they’re dealing with and instantiate a PKey subclass themselves, placing the result in connect_kwargs.pkey.
env.no_agent, which is a renaming/inversion of Paramiko’s allow_agent connect kwarg Ported Users who were setting this to True should now simply set connect_kwargs.allow_agent to False instead.
env.no_keys, similar to no_agent, just an inversion of the look_for_keys connect kwarg Ported Use connect_kwargs.look_for_keys instead (setting it to False to disable Paramiko’s default key-finding behavior.)
env.passwords (and env.sudo_passwords) stores connection/sudo passwords in a dict keyed by host strings Ported/Pending

Each fabric.connection.Connection object may be configured with its own connect_kwargs given at instantiation time, allowing for per-host password configuration already.

However, we expect users may want a simpler way to set configuration values that are turned into implicit fabric.connection.Connection objects automatically; such a feature is still pending.

Configuring IdentityFile in one’s ssh_config Ported Still honored, along with a bunch of newly honored ssh_config settings; see Loading and using ssh_config files.

File transfer

The below feature breakdown applies to the put and/or get “operation” functions from v1.

Transferring individual files owned by the local and remote user Ported

Basic file transfer in either direction works and is offered as fabric.connection.Connection.get/fabric.connection.Connection.put (though the code is split out into a separate-responsibility class, fabric.transfer.Transfer.)

The signature of these methods has been cleaned up compared to v1, though their positional-argument essence (get(remote, local) and put(local, remote) remains the same.

Omit the ‘destination’ argument for implicit ‘relative to local context’ behavior (e.g. put("local.txt") implicitly uploading to remote $HOME/local.txt.) Ported You should probably still be explicit, because this is Python.
Use either file paths or file-like objects on either side of the transfer operation (e.g. uploading a StringIO instead of an on-disk file) Ported This was a useful enough and simple enough trick to keep around.
Preservation of source file mode at destination (e.g. ensuring an executable bit that would otherwise be dropped by the destination’s umask, is re-added.) Ported Not only was this ported, but it is now the default behavior. It may be disabled via kwarg if desired.
Bundled sudo operations as part of file transfer Removed

This was one of the absolute buggiest parts of v1 and never truly did anything users could not do themselves with a followup call to sudo, so we opted not to port it.

Should enough users pine for its loss, we may reconsider, but if we do it will be with a serious eye towards simplification and/or an approach not involving intermediate files.

Recursive multi-file transfer (e.g. put(a_directory) uploads entire directory and all its contents) Removed

This was another one of the buggiest parts of v1, and over time it became clear that its maintenance burden far outweighed the fact that it was poorly reinventing rsync and/or the use of archival file tools like ye olde tar``+``gzip.

For one potential workaround, see the rsync function in patchwork.

Remote file path tilde expansion Removed This behavior is ultimately unnecessary (one can simply leave the tilde off for the same result) and had a few pernicious bugs of its own, so it’s gone.
Naming downloaded files after some aspect of the remote destination, to avoid overwriting during multi-server actions Pending This falls under the Group family, which still needs some work in this regard.

Configuration

In general, configuration has been massively improved over the old fabricrc files; most config logic comes from Invoke’s configuration system, which offers a full-fledged configuration hierarchy (in-code config, multiple config file locations, environment variables, CLI flags, and more) and multiple file formats. Nearly all configuration avenues in Fabric 1 become, in modern Fabric, manipulation of whatever part of the config hierarchy is most appropriate for your needs.

Modern versions of Fabric only make minor modifications to (or parameterizations of) Invoke’s setup; see our locally-specific config doc page for details.

Note

Make sure to look elsewhere in this document for details on any given v1 env setting, as many have moved outside the configuration system into object or method keyword arguments.

Modifying fabric.(api.)env directly Ported To effect truly global-scale config changes, use config files, task-collection-level config data, or the invoking shell’s environment variables.
Making locally scoped fabric.env changes via with settings(...): or its decorator equivalent, @with_settings Ported/Pending

Most of the use cases surrounding settings are now served by the fact that fabric.connection.Connection objects keep per-host/connection state - the pattern of switching the implicit global context around was a design antipattern which is now gone.

The remaining such use cases have been turned into context-manager methods of fabric.connection.Connection (or its parent class), or have such methods pending.

SSH config file loading (off by default, limited to ~/.ssh/config only unless configured to a different, single path) Ported

Much improved: SSH config file loading is on by default (which can be changed), multiple sources are loaded and merged just like OpenSSH, and more besides; see Loading and using ssh_config files.

In addition, we’ve added support for some ssh_config directives which were ignored by v1, such as ConnectTimeout and ProxyCommand, and going forwards we intend to support as much of ssh_config as is reasonably possible.

contrib

The old contrib module represented “best practice” functions that did not, themselves, require core support from the rest of Fabric but were built using the same primitives available to users.

In modern Fabric, that responsibility has been removed from the core library into other standalone libraries which have their own identity & release process, typically either invocations (local-oriented code that does not use SSH) or patchwork (primarily remote-oriented code, though anything not explicitly dealing with both ends of the connection will work just as well locally.)

Those libraries are still a work in progress, not least because we still need to identify the best way to bridge the gap between them (as many operations are not intrinsically local-or-remote but can work on either end.)

Since they are by definition built on the core APIs available to all users, they currently get less development focus; users can always implement their own versions without sacrificing much (something less true for the core libraries.) We expect to put more work into curating these collections once the core APIs have settled down.

Details about what happened to each individual chunk of fabric.contrib are in the below table:

console.confirm for easy bool-returning confirmation prompts Ported Moved to invocations.console.confirm, with minor signature tweaks.
django.*, supporting integration with a local Django project re: importing and using Django models and other code Removed We aren’t even sure if this is useful a decade after it was written, given how much Django has surely changed since then. If you’re reading and are sad that this is gone, let us know!
files.* (e.g. exists, append, contains etc) for interrogating and modifying remote files Ported/Pending

Many of the more useful functions in this file have been ported to patchwork.files but are still in an essentially alpha state.

Others, such as is_link, comment/uncomment, etc have not been ported yet. If they are, the are likely to end up in the same place.

project.rsync_project for rsyncing the entire host project remotely Ported Now patchwork.transfers.rsync, with some modifications.
project.rsync_project for uploading host project via archive file and scp Removed This did not seem worth porting; the overall pattern of “copy my local bits remotely” is already arguably an antipattern (vs repeatable deploys of artifacts, or at least remote checkout of a VCS tag) and if one is going down that road anyways, rsync is a much smarter choice.

fabric.env reference

Many/most of the members in v1’s fabric.env are covered in the above per-topic sections; any that are not covered elsewhere, live here. All are explicitly noted as env.<name> for ease of searching in your browser or viewer.

A small handful of env vars were never publicly documented & were thus implicitly private; those are not represented here.

env.abort_exception for setting which exception is used to abort Removed Aborting as a concept is gone, just raise whatever exception seems most reasonable to surface to an end user, or use Exit. See also Utilities.
env.all_hosts and env.tasks listing execution targets Ported/Pending

Fabric’s Executor subclass stores references to all CLI parsing results (including the value of --hosts, the tasks requested and their args, etc) and the intent is for users to have access to that information.

However, the details for that API (e.g. exposing the executor via a task’s Context/fabric.connection.Connection) are still in flux.

env.command noting currently executing task name (in hindsight, quite the misnomer…) Ported/Pending See the notes for env.all_hosts above - same applies here re: user visibility into CLI parsing results.
env.command_prefixes for visibility into (arguably also mutation of) the shell command prefixes to be applied to run/sudo Ported This is now command_prefixes.
env.cwd noting current intended working directory Ported

This is now command_cwds (a list, not a single string, to more properly model the intended contextmanager-driven use case.)

Note that remote-vs-local context for this data isn’t yet set up; see the notes about with cd under Shell command execution (local/run/sudo).

env.dedupe_hosts controlling whether duplicate hosts in merged host lists get deduplicated or not Pending Not ported yet, will probably get tackled as part of roles/host lists overhaul.
env.echo_stdin (undocumented) for turning off the default echoing of standard input Ported Is now a config option under the run tree, with much the same behavior.
env.local_user for read-only access to the discovered local username Removed We’re not entirely sure why v1 felt this was worth caching in the config; if you need this info, just import and call fabric.util.get_local_user.
env.output_prefix determining whether or not line-by-line host-string prefixes are displayed Pending Differentiating parallel stdout/err is still a work in progress; we may end up reusing line-by-line logging and prefixing (ideally via actual logging) or we may try for something cleaner such as streaming to per-connection log files.
env.prompts controlling prompt auto-response Ported Prompt auto-response is now publicly implemented as the StreamWatcher and Responder class hierarchy, instances of which can be handed to run via kwarg or stored globally in the config as run.watchers.
env.real_fabfile storing read-only fabfile path which was loaded by the CLI machinery Ported The loaded task Collection is stored on both the top level Program object as well as the Executor which calls tasks; and Collection has a loaded_from attribute with this information.
env.remote_interrupt controlling how interrupts (i.e. a local KeyboardInterrupt are caught, forwarded or other Ported/Removed

Invoke’s interrupt capture behavior is currently “always just send the interrupt character to the subprocess and continue”, allowing subprocesses to handle ^C however they need to, which is an improvement over Fabric 1 and roughly equivalent to setting env.remote_interrupt = True.

Allowing users to change this behavior via config is not yet implemented, and may not be, depending on whether anybody needs it - it was added as an option in v1 for backwards compat reasons.

It is also technically possible to change interrupt behavior by subclassing and overriding invoke.runners.Runner.send_interrupt.

env.roles, env.roledefs and env.effective_roles controlling/exposing what roles are available or currently in play Pending

As noted in API organization, roles as a concept were ported to fabric.group.Group, but there’s no central clearinghouse in which to store them.

We may delegate this to userland forever, but seems likely a common-best-practice option (such as creating Groups from some configuration subtree and storing them as a Context attribute) will appear in early 2.x.

env.ok_ret_codes for overriding the default “0 good, non-0 bad” error detection for subprocess commands Pending Not ported yet, but should involve some presumably minor updates to invoke.runners.Runner.generate_result and Result.
env.sudo_prefix determining the sudo binary name + its flags used when creating sudo command strings Pending Sudo command construction does not currently look at the config for anything but the actual sudo prompt.
env.sudo_prompt for setting the prompt string handed to sudo (and then expected in return for auto-replying with a configured password) Ported Is now sudo.prompt in the configuration system.
env.use_exceptions_for to note which actions raise exceptions Removed As with most other functionality surrounding Fabric 1’s “jump straight to sys.exit” design antipattern, this is gone - modern Fabric will not be hiding any exceptions from user-level code.
env.use_ssh_config to enable off-by-default SSH config loading Ported SSH config loading is now on by default, but an option remains to disable it. See Configuration for more.
env.version exposing current Fabric version number Removed Just import fabric and reference fabric.__version__ (string) or fabric.__version_info__ (tuple).

Example upgrade process

This section goes over upgrading a small but nontrivial Fabric 1 fabfile to work with modern Fabric. It’s not meant to be exhaustive, merely illustrative; for a full list of how to upgrade individual features or concepts, see Upgrade specifics.

Sample original fabfile

Here’s a (slightly modified to concur with ‘modern’ Fabric 1 best practices) copy of Fabric 1’s final tutorial snippet, which we will use as our test case for upgrading:

from fabric.api import abort, env, local, run, settings, task
from fabric.contrib.console import confirm

env.hosts = ["my-server"]

@task
def test():
    with settings(warn_only=True):
        result = local("./manage.py test my_app", capture=True)
    if result.failed and not confirm("Tests failed. Continue anyway?"):
        abort("Aborting at user request.")

@task
def commit():
    local("git add -p && git commit")

@task
def push():
    local("git push")

@task
def prepare_deploy():
    test()
    commit()
    push()

@task
def deploy():
    code_dir = "/srv/django/myproject"
    with settings(warn_only=True):
        if run("test -d {}".format(code_dir)).failed:
            cmd = "git clone [email protected]:/path/to/repo/.git {}"
            run(cmd.format(code_dir))
    with cd(code_dir):
        run("git pull")
        run("touch app.wsgi")

We’ll port this directly, meaning the result will still be fabfile.py, though we’d like to note that writing your code in a more library-oriented fashion - even just as functions not wrapped in @task - can make testing and reusing code easier.

Imports

In modern Fabric, we don’t need to import nearly as many functions, due to the emphasis on object methods instead of global functions. We only need the following:

  • Exit, a friendlier way of requesting a sys.exit;
  • @task, as before, but coming from Invoke as it’s not SSH-specific;
  • confirm, which now comes from the Invocations library (also not SSH-specific; though Invocations is one of the descendants of fabric.contrib, which no longer exists);
from fabric import task
from invoke import Exit
from invocations.console import confirm

Host list

The idea of a predefined global host list is gone; there is currently no direct replacement. In general, users can set up their own execution context, creating explicit fabric.connection.Connection and/or fabric.group.Group objects as needed; core Fabric is in the process of building convenience helpers on top of this, but “create your own Connections” will always be there as a backstop.

Speaking of convenience helpers: most of the functionality of fab --hosts and @hosts has been ported over – the former directly (see --hosts), the latter as a @task keyword argument. Thus, for now our example will be turning the global env.hosts into a lightweight module-level variable declaration, intended for use in the subsequent calls to @task:

my_hosts = ["my-server"]

Note

This is an area under active development, so feedback is welcomed.

Test task

The first task in the fabfile uses a good spread of the API. We’ll outline the changes here (though again, all details are in Upgrade specifics):

  • Declaring a function as a task is nearly the same as before: use a @task decorator (which, in modern Fabric, can take more optional keyword arguments than its predecessor, including some which replace some of v1’s decorators).
  • @task-wrapped functions must now take an explicit initial context argument, whose value will be a fabric.connection.Connection object at runtime.
  • The use of with settings(warn_only=True) can be replaced by a simple kwarg to the local call.
  • That local call is now a method call on the fabric.connection.Connection, fabric.connection.Connection.local.
  • capture is no longer a useful argument; we can now capture and display at the same time, locally or remotely. If you don’t actually want a local subprocess to mirror its stdout/err while it runs, you can simply say hide=True (or hide="stdout" or etc.)
  • Result objects are pretty similar between versions; modern Fabric’s results no longer pretend to “be” strings, but instead act more like booleans, acting truthy if the command exited cleanly, and falsey otherwise. In terms of attributes exhibited, most of the same info is available, and more besides.
  • abort is gone; you should use whatever exceptions you feel are appropriate, or Exit for a sys.exit equivalent. (Or just call sys.exit if you want a no-questions-asked immediate exit that even our CLI machinery won’t touch.)

The result:

@task
def test(c):
    result = c.local("./manage.py test my_app", warn=True)
    if not result and not confirm("Tests failed. Continue anyway?"):
        raise Exit("Aborting at user request.")

Other simple tasks

The next two tasks are simple one-liners, and you’ve already seen what replaced the global local function:

@task
def commit(c):
    c.local("git add -p && git commit")

@task
def push(c):
    c.local("git push")

Calling tasks from other tasks

This is another area that is in flux at the Invoke level, but for now, we can simply call the other tasks as functions, just as was done in v1. The main difference is that we want to pass along our context object to preserve the configuration context (such as loaded config files or CLI flags):

@task
def prepare_deploy(c):
    test(c)
    commit(c)
    push(c)

Actual remote steps

Note that up to this point, nothing truly Fabric-related has been in play - fabric.connection.Connection.local is just a rebinding of Context.run, Invoke’s local subprocess execution method. Now we get to the actual deploy step, which invokes fabric.connection.Connection.run instead, executing remotely (on whichever host the fabric.connection.Connection has been bound to).

with cd is not fully implemented for the remote side of things, but we expect it will be soon. For now we fall back to command chaining with &&. And, notably, now that we care about selecting host targets, we refer to our earlier definition of a default host list – my_hosts – when declaring the default host list for this task.

@task(hosts=my_hosts)
def deploy(c):
    code_dir = "/srv/django/myproject"
    if not c.run("test -d {}".format(code_dir), warn=True):
        cmd = "git clone [email protected]:/path/to/repo/.git {}"
        c.run(cmd.format(code_dir))
    c.run("cd {} && git pull".format(code_dir))
    c.run("cd {} && touch app.wsgi".format(code_dir))

The whole thing

Now we have the entire, upgraded fabfile that will work with modern Fabric:

from invoke import Exit
from invocations.console import confirm

from fabric import task

my_hosts = ["my-server"]

@task
def test(c):
    result = c.local("./manage.py test my_app", warn=True)
    if not result and not confirm("Tests failed. Continue anyway?"):
        raise Exit("Aborting at user request.")

@task
def commit(c):
    c.local("git add -p && git commit")

@task
def push(c):
    c.local("git push")

@task
def prepare_deploy(c):
    test(c)
    commit(c)
    push(c)

@task(hosts=my_hosts)
def deploy(c):
    code_dir = "/srv/django/myproject"
    if not c.run("test -d {}".format(code_dir), warn=True):
        cmd = "git clone [email protected]:/path/to/repo/.git {}"
        c.run(cmd.format(code_dir))
    c.run("cd {} && git pull".format(code_dir))
    c.run("cd {} && touch app.wsgi".format(code_dir))