Changes in version 0.9

This document details the various backwards-incompatible changes made during Fabric’s rewrite between versions 0.1 and 0.9. The codebase has been almost completely rewritten and reorganized and an attempt has been made to remove “magical” behavior and make things more simple and Pythonic; the fab command-line component has also been redone to behave more like a typical Unix program.

Major changes

You’ll want to at least skim the entire document, but the primary changes that will need to be made to one’s fabfiles are as follows:

Imports

You will need to explicitly import any and all methods or decorators used, at the top of your fabfile; they are no longer magically available. Here’s a sample fabfile that worked with 0.1 and earlier:

@hosts('a', 'b')
def my_task():
    run('ls /var/www')
    sudo('mkdir /var/www/newsite')

The above fabfile uses hosts, run and sudo, and so in Fabric 0.9 one simply needs to import those objects from the new API module fabric.api:

from fabric.api import hosts, run, sudo

@hosts('a', 'b')
def my_task():
    run('ls /var/www')
    sudo('mkdir /var/www/newsite')

You may, if you wish, use from fabric.api import *, though this is technically not Python best practices; or you may import directly from the Fabric submodules (e.g. from fabric.decorators import hosts.) See Fabfile construction and use for more information.

Python version

Fabric started out Python 2.5-only, but became largely 2.4 compatible at one point during its lifetime. Fabric is once again only compatible with Python 2.5 or newer, in order to take advantage of the various new features and functions available in that version.

With this change we’re setting an official policy to support the two most recent stable releases of the Python 2.x line, which at time of writing is 2.5 and 2.6. We feel this is a decent compromise between new features and the reality of operating system packaging concerns. Given that most users use Fabric from their workstations, which are typically more up-to-date than servers, we’re hoping this doesn’t cut out too many folks.

Finally, note that while we will not officially support a 2.4-compatible version or fork, we may provide a link to such a project if one arises.

Environment/config variables

The config object previously used to access and set internal state (including Fabric config options) has been renamed to env, but otherwise remains mostly the same (it allows both dictionary and object-attribute style access to its data.) env resides in the state submodule and is importable via fabric.api, so where before one might have seen fabfiles like this:

def my_task():
    config.foo = 'bar'

one will now be explicitly importing the object like so:

from fabric.api import env

def my_task():
    env.foo = 'bar'

Execution mode

Fabric’s default mode of use, in prior versions, was what we called “broad mode”: your tasks, as Python code, ran only once, and any calls to functions that made connections (such as run or sudo) would run once per host in the current host list. We also offered “deep mode”, in which your entire task function would run once per host.

In Fabric 0.9, this dichotomy has been removed, and “deep mode” is the method Fabric uses to perform all operations. This allows you to treat your Fabfiles much more like regular Python code, including the use of if statements and so forth, and allows operations like run to unambiguously return the output from the server.

Other modes of execution such as the old “broad mode” may return as Fabric’s internals are refactored and expanded, but for now we’ve simplified things, and deep mode made the most sense as the primary mode of use.

“Lazy” string interpolation

Because of how Fabric used to run in “broad mode” (see previous section) a special string formatting technique – the use of a bash-like dollar sign notation, e.g. "hostname: $(fab_host)" – had to be used to allow the current state of execution to be represented in one’s operations. This is no longer necessary and has been removed. Because your tasks are executed once per host, you may build strings normally (e.g. with the % operator) and refer to env.host_string, env.user and so forth.

For example, Fabric 0.1 had to insert the current username like so:

print("Your current username is $(fab_user)")

Fabric 0.9 and up simply reference env variables as normal:

print("Your current username is %s" % env.user)

As with the execution modes, a special string interpolation function or method that automatically makes use of env values may find its way back into Fabric at some point if a need becomes apparent.

Other backwards-incompatible changes

In no particular order:

  • The Fabric config file location used to be ~/.fabric; in the interests of honoring Unix filename conventions, it’s now ~/.fabricrc.

  • The old config object (now env) had a getAny method which took one or more key strings as arguments, and returned the value attached to the first valid key. This method still exists but has been renamed to first.

  • Environment variables such as fab_host have been renamed to simply e.g. host. This looks cleaner and feels more natural, and requires less typing. Users will naturally need to be careful not to override these variables, but the same holds true for e.g. Python’s builtin methods and types already, so we felt it was worth the tradeoff.

  • Fabric’s version header is no longer printed every time the program runs; you should now use the standard --version/-V command-line options to print version and exit.

  • The old about command has been removed; other Unix programs don’t typically offer this. Users can always view the license and warranty info in their respective text files distributed with the software.

  • The old help command is now the typical Unix options -h/--help.

    • Furthermore, there is no longer a listing of Fabric’s programming API available through the command line – those topics impact fabfile authors, not fab users (even though the former is a subset of the latter) and should stay in the documentation only.
  • prompt‘s primary function is now to return a value to the caller, although it may still optionally store the entered value in env as well.

  • prompt now considers the empty string to be valid input; this allows other functions to wrap prompt and handle “empty” input on their own terms.

  • In addition to the above changes, prompt has been updated to behave more obviously, as its previous behavior was confusing in a few ways:

    • It will now overwrite pre-existing values in the environment dict, but will print a warning to the user if it does so.
    • Additionally, (and this appeared to be undocumented) the default argument could take a callable as well as a string, and would simply set the default message to the return value if a callable was given. This seemed to add unnecessary complexity (given that users may call e.g. prompt(blah, msg, default=my_callable()) so it has been removed.
  • When connecting, Fabric used to use the undocumented fab_pkey env variable as a method of passing in a Paramiko PKey object to the SSH client’s connect method. This has been removed in favor of an ssh-like -i option, which allows one to specify a private key file to use; that should generally be enough for most users.

  • download is now get in order to match up with put (the name mismatch was due to get being the old method of getting env vars.)

  • The noshell argument to sudo (added late in its life to previous Fabric versions) has been renamed to shell (defaults to True, so the effective behavior remains the same) and has also been extended to the run operation.

    • Additionally, the global sudo_noshell option has been renamed to use_shell and also applies to both run and sudo.
  • local_per_host has been removed, as it only applied to the now-removed “broad mode”.

  • load has been removed; Fabric is now “just Python”, so use Python’s import mechanisms in order to stitch multiple fabfiles together.

  • abort is no longer an “operation” per se and has been moved to fabric.utils. It is otherwise the same as before, taking a single string message, printing it to the user and then calling sys.exit(1).

  • rsyncproject and upload_project have been moved into fabric.contrib (specifically, fabric.contrib.project), which is intended to be a new tree of submodules for housing “extra” code which may build on top of the core Fabric operations.

  • invoke has been turned on its head, and is now the runs_once decorator (living in fabric.decorators). When used to decorate a function, that function will only execute one time during the lifetime of a fab run. Thus, where you might have used invoke multiple times to ensure a given command only runs once, you may now use runs_once to decorate the function and then call it multiple times in a normal fashion.

  • It looks like the regex behavior of the validate argument to prompt was never actually implemented. It now works as advertised.

  • Couldn’t think of a good reason for require to be a decorator and a function, and the function is more versatile in terms of where it may be used, so the decorator has been removed.

  • As things currently stand with the execution model, the depends decorator doesn’t make a lot of sense: instead, it’s safest/best to simply make “meta” commands that just call whatever chain of “real” commands you need performed for a given overarching task.

    For example, instead of having command A say that it “depends on” command B, create a command C which calls A and B in the right order, e.g.:

    def build():
        local('make clean all')
    
    def upload():
        put('app.tgz', '/tmp/app.tgz')
        run('tar xzf /tmp/app.tgz')
    
    def symlink():
        run('ln -s /srv/media/photos /var/www/app/photos')
    
    def deploy():
        build()
        upload()
        symlink()
    

    Note

    The execution model is still subject to change as Fabric evolves. Please don’t hesitate to email the list or the developers if you have a use case that needs something Fabric doesn’t provide right now!

  • Removed the old fab shell functionality, since the move to “just Python” should make vanilla python/ipython usage of Fabric much easier.

    • We may add it back in later as a convenient shortcut to what basically amounts to running ipython and performing a handful of from fabric.foo import bar calls.
  • The undocumented fab_quiet option has been replaced by a much more granular set of output controls. For more info, see Managing output.

Changes from alpha 1 to alpha 2

The below list was generated by running git shortlog 0.9a1..0.9a2 and then manually sifting through and editing the resulting commit messages. This will probably occur for the rest of the alphas and betas; we hope to use Sphinx-specific methods of documenting changes once the final release is out the door.

  • Various minor tweaks to the (still in-progress) documentation, including one thanks to Curt Micol.
  • Added a number of TODO items based on user feedback (thanks!)
  • Host information now available in granular form (user, host, port) in the env dict, alongside the full user@host:port host string.
  • Parsing of host strings is now more lenient when examining the username (e.g. hyphens.)
  • User/host info no longer cleared out between commands.
  • Tweaked setup.py to use find_packages. Thanks to Pat McNerthney.
  • Added ‘capture’ argument to local to allow local interactive tasks.
  • Reversed default value of local‘s show_stderr kwarg; local stderr now prints by default instead of being hidden by default.
  • Various internal fabfile tweaks.

Changes from alpha 2 to alpha 3

  • Lots of updates to the documentation and TODO
  • Added contrib.files with a handful of file-centric subroutines
  • Added contrib.console for console UI stuff (so far, just confirm)
  • Reworked config file mechanisms a bit, added CLI flag for setting it.
  • Output controls (including CLI args, documentation) have been added
  • Test coverage tweaked and grown a small amount (thanks in part to Peter Ellis)
  • Roles overhauled/fixed (more like hosts now)
  • Changed --list linewrap behavior to truncate instead.
  • Make private key passphrase prompting more obvious to users.
  • Add pty option to sudo. Thanks to José Muanis for the tip-off re: get_pty()
  • Add CLI argument for setting the shell used in commands (thanks to Steve Steiner)
  • Only load host keys when env.reject_unknown_keys is True. Thanks to Pat McNerthney.
  • And many, many additional bugfixes and behavioral tweaks too small to merit cluttering up this list! Thanks as always to everyone who contributed bugfixes, feedback and/or patches.

Changes from alpha 3 to beta 1

This is closer to being a straight dump of the Git changelog than the previous sections; apologies for the overall change in tense.

  • Add autodocs for fabric.contrib.console.
  • Minor cleanup to package init and setup.py.
  • Handle exceptions with strerror attributes that are None instead of strings.
  • contrib.files.append may now take a list of strings if desired.
  • Straighten out how prompt() deals with trailing whitespace
  • Add ‘cd’ context manager.
  • Update upload_template to correctly handle backing up target directories.
  • upload_template() can now use Jinja2 if it’s installed and user asks for it.
  • Handle case where remote host SSH key doesn’t match known_hosts.
  • Fix race condition in run/sudo.
  • Start fledgling FAQ; extended pty option to run(); related doc tweaks.
  • Bring local() in line with run()/sudo() in terms of .failed attribute.
  • Add dollar-sign backslash escaping to run/sudo.
  • Add FAQ question re: backgrounding processes.
  • Extend some of put()’s niceties to get(), plus docstring/comment updates
  • Add debug output of chosen fabfile for troubleshooting fabfile discovery.
  • Fix Python path bug which sometimes caused Fabric’s internal fabfile to pre-empt user’s fabfile during load phase.
  • Gracefully handle “display” for tasks with no docstring.
  • Fix edge case that comes up during some auth/prompt situations.
  • Handle carriage returns in output_thread correctly. Thanks to Brian Rosner.

Changes from beta 1 to release candidate 1

As with the previous changelog, this is also mostly a dump of the Git log. We promise that future changelogs will be more verbose :)

  • Near-total overhaul and expansion of documentation (this is the big one!) Other mentions of documentation in this list are items deserving their own mention, e.g. FAQ updates.
  • Add FAQ question re: passphrase/password prompt
  • Vendorized Paramiko: it is now included in our distribution and is no longer an external dependency, at least until upstream fixes a nasty 1.7.5 bug.
  • Fix #34: switch upload_template to use mkstemp (also removes Python 2.5.2+ dependency – now works on 2.5.0 and up)
  • Fix #62 by escaping backticks.
  • Replace “ls” with “test” in exists()
  • Fixes #50. Thanks to Alex Koshelev for the patch.
  • local‘s return value now exhibits .return_code.
  • Abort on bad role names instead of blowing up.
  • Turn off DeprecationWarning when importing paramiko.
  • Attempted fix re #32 (dropped output)
  • Update role/host initialization logic (was missing some edge cases)
  • Add note to install docs re: PyCrypto on win32.
  • Add FAQ item re: changing env.shell.
  • Rest of TODO migrated to tickets.
  • fab test (when in source tree) now uses doctests.
  • Add note to compatibility page re: fab_quiet.
  • Update local() to honor context_managers.cd()

Changes from release candidate 1 to final release

  • Fixed the sed docstring to accurately reflect which sed options it uses.
  • Various changes to internal fabfile, version mechanisms, and other non-user-facing things.