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Sunday, November 23, 2014

More fabric as a library

Recently I had to prepare a tool doing some remote commands, so of course I decided to use fabric, but I have big problem to control hosts. I remembered that I had written a short article on Fabric in here some time ago. But it didn't help. I asked on the Fabric mailing lists, but there was no help.


Manual host name control

In this tool I didn't need to run many parallel SSH connection, so I decided to control remote host name from inside the loop in the function my setting env.host_string each time (this is very useful functionality). Like in following example:


#!/usr/bin/env python
"""Example code to use Fabric as a library. 
It shows how to set up host manually.
 
Author: Wawrzek Niewodniczanski < main at wawrzek dot name >
"""
 
# import sys to deal with scripts arguments and of course fabric 
import sys
import fabric
from fabric.api import run, hide, env

env.hosts = ['host1', 'host2'] 
 
# Main function to run remote task 
def run_task(task='uname'):
    """run_task([task]) -
    runs a command on a remote server. If task is not specify it will run 'uname'."""
    # hide some information (this is not necessary).
    with hide('running', 'status'):
        run(task) 
 
# Main loop
# take all arguments and run them on all hosts specify in env.hosts variable
# if not arguments run 'uname' 
if len(sys.argv) > 1:
    tasks = sys.argv[1:]
    for task in tasks:
        for host in env.hosts:
            env.host_string = host
            run_task(task)
else:
    for host in env.hosts:
        run_task() 



Fabric in full control

The problem bugged me since then. Yesterday I found some of my old code. Analysed it and quickly found small, but profound difference with mu recent fabric usage. Rhe code above called the run_task function wrongly. Rather than dealt it in the normal way I supposed to use execute.

#!/usr/bin/env python
"""Example code to use Fabric as a library. 
It shows how to set up host manually.
 
Author: Wawrzek Niewodniczanski < main at wawrzek dot name >
"""
 
# import sys to deal with scripts arguments and of course fabric 
import sys
import fabric
from fabric.api import run, hide, env, execute

env.hosts = ['host1', 'host2'] 
 
# Main function to run remote task 
def run_task(task='uname'):
    """run_task([task]) -
    runs a command on a remote server. If task is not specify it will run 'uname'."""
    # hide some information (this is not necessary).
    with hide('running', 'status'):
        run(task) 
 
# Main loop
# take all arguments and run them on all hosts specify in env.hosts variable
# if not arguments run 'uname' 
if len(sys.argv) > 1:
    tasks = sys.argv[1:]
    for task in tasks:
        execute(run_task, task)
else:
    execute(run_task)


Links:

http://www.fabfile.org/
http://larryn.blogspot.co.uk/2012/11/fabric-as-python-module.html
http://lists.nongnu.org/archive/html/fab-user/2014-10/msg00002.html
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