some fabric trap and tricks

Fabric is a Python (2.5-2.7) library and command-line tool for streamlining the use of SSH for application deployment or systems administration tasks. Here’s some trap and tricks I met and got from my usual use.

trap 1: operation error  cause execution abort
fabric operations like run or put, would cause task execute to fail when error occured.
run fab with -w option, or turn on warn_only temporarily with code like this:

with settings(warn_only = True):
    run('some commmand')

trap 2. low level network error cause execution abort
Low level network error like name resolve error, connection timeout, connection refuesed, would normally cause execution abort.
catch NetworkError exception like this:

from fabric.exceptions import NetworkError
def some_task():
    except NetworkError as e:
        print e

trap 3. too many connection/thread cause execution abort
Fabric will keep a connection cache for performance, but when you are running task on thousands of hosts, Fabric may run out of resource(especially reach thread limit) with error message like thread.error: can’t start new thread
turn on eagerly_disconnect setting to close connection resource as soon as possible

env.eagerly_disconnect = True

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