Handling failures with Fabric

Question

I'm trying to handle failure on fabric, but the example I saw on the docs was too localized for my taste. I need to execute rollback actions if any of a number of actions fail. I tried, then, to use contexts to handle it, like this:

@_contextmanager
def failwrapper():
    with settings(warn_only=True):
        result = yield
    if result.failed:
        rollback()
        abort("********* Failed to execute deploy! *********")

And then

@task
def deploy():
    with failwrapper():
        updateCode()
        migrateDb()
        restartServer()

Unfortunately, when one of these tasks fail, I do not get anything on result.

Is there any way of accomplishing this? Or is there another way of handling such situations?

Answer 1

According to my tests, you can accomplish that with this:

from contextlib import contextmanager

@contextmanager
def failwrapper():
    try:
        yield
    except SystemExit:
        rollback()
        abort("********* Failed to execute deploy! *********")

As you can see I got rid of the warn_only setting as I suppose you don't need it if the rollback can be executed and you're aborting the execution anyway with abort().

Fabric raises SystemExit exception when encountering errors and warn_only setting is not used. We can just catch the exception and do the rollback.

Answer 2

Following on from Henri's answer, this also handles keyboard interrupts (Ctrl-C) and other exceptions:

@_contextmanager
def failwrapper():
    try:
        yield
    except:
        rollback()
        raise