当 Fabric 收到错误时如何继续任务

当我定义要在多个远程服务器上运行的任务时，如果该任务在服务器1上运行并退出时出现错误，Fabric 将停止并中止该任务。但是我想让结构忽略这个错误，并在下一个服务器上运行这个任务。我怎么才能让它这么做呢？

例如:

$ fab site1_service_gw
[site1rpt1] Executing task 'site1_service_gw'


[site1fep1] run: echo 'Nm123!@#' | sudo -S route
[site1fep1] err:
[site1fep1] err: We trust you have received the usual lecture from the local System
[site1fep1] err: Administrator. It usually boils down to these three things:
[site1fep1] err:
[site1fep1] err:     #1) Respect the privacy of others.
[site1fep1] err:     #2) Think before you type.
[site1fep1] err:     #3) With great power comes great responsibility.
[site1fep1] err: root's password:
[site1fep1] err: sudo: route: command not found


Fatal error: run() encountered an error (return code 1) while executing 'echo 'Nm123!@#' | sudo -S route '


Aborting.
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最佳答案

From the docs:

... Fabric defaults to a “fail-fast” behavior pattern: if anything goes wrong, such as a remote program returning a nonzero return value or your fabfile’s Python code encountering an exception, execution will halt immediately.

This is typically the desired behavior, but there are many exceptions to the rule, so Fabric provides env.warn_only, a Boolean setting. It defaults to False, meaning an error condition will result in the program aborting immediately. However, if env.warn_only is set to True at the time of failure – with, say, the settings context manager – Fabric will emit a warning message but continue executing.

Looks like you can exercise fine-grained control over where errors are ignored by using the settings context manager, something like so:

from fabric.api import settings


sudo('mkdir tmp') # can't fail
with settings(warn_only=True):
sudo('touch tmp/test') # can fail
sudo('rm tmp') # can't fail
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You can also set the entire script's warn_only setting to be true with 

def local():
env.warn_only = True
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In Fabric 1.3.2 at least, you can recover the exception by catching the SystemExit exception. That's helpful if you have more than one command to run in a batch (like a deploy) and want to cleanup if one of them fails.

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As of Fabric 1.5, there is a ContextManager that makes this easier:

from fabric.api import sudo, warn_only


with warn_only():
sudo('mkdir foo')

Update: I re-confirmed that this works in ipython using the following code.

from fabric.api import local, warn_only


#aborted with SystemExit after 'bad command'
local('bad command'); local('bad command 2')


#executes both commands, printing errors for each
with warn_only():
local('bad command'); local('bad command 2')
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You should set the abort_exception environment variable and catch the exception.

For example:

from fabric.api        import env
from fabric.operations import sudo


class FabricException(Exception):
pass


env.abort_exception = FabricException
# ... set up the rest of the environment...


try:
sudo('reboot')
except FabricException:
pass  # This is expected, we can continue.

You can also set it in a with block. See the documentation here.

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In my case, on Fabric >= 1.4 this answer was the correct one.

You can skip bad hosts by adding this:

env.skip_bad_hosts = True

Or passing the --skip-bad-hosts flag/

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In Fabric 2.x you can just use invoke's run with the warn=True argument. Anyway, invoke is a dependency of Fabric 2.x:

from invoke import run
run('bad command', warn=True)

From within a task:

from invoke import task


@task
def my_task(c):
c.run('bad command', warn=True)

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