Re: [Fab-user] Can't save output to a CSV file if running task in parallel

[Brandon Whaley]

Parallel uses multiprocessing, so you're opening output.csv in write mode once per host.  You'll need to have a master task consolidate the return values of your parallel subtask (use execute) and write the csv once everything is done.  Remember that execute returns a dictionary whose keys are the host_strings of each host and the values are the return value of the function you're executing.

On Thu, Sep 10, 2015 at 4:46 PM Felix Almeida <address@hidden> wrote:

Hi all,

I'm trying to run a simple task in parallel that captures the OS type (Linux, AIX, HP-UX, etc.) of a set of UNIX servers and save this information into a CSV file.

However, if I add the @parallel decorator to the task the CSV file is left empty (only the header is saved), but if I remove the @parallel decorator then everything goes well. Note that the output to the screen via puts works fine in both cases.

Please, any ideas of what I'm doing wrong?

Perhaps this is not even a fabric question but a Python one (I'm not sure, sorry).

Here is the complete code:

import csv
from fabric.api import env, task, runs_once, parallel, execute, run, puts, hide

env.abort_on_prompts = True
env.always_use_pty = False
env.command_timeout = 3
env.disable_known_hosts = True
env.eagerly_disconnect = True
env.timeout = 3
env.use_shell = False
env.warn_only = True

@parallel(pool_size=5)
def _run(csv_output):
    try:
        with hide('output', 'running'):
            out = run('uname')
    except SystemExit:
        msg = 'error: a password is being requested'
    else:
        msg = str(out)
    puts(msg)
    csv_output.writerow([env.host, msg])
    return str(out)

@task
@runs_once
def run_uname(hosts_file=None):
    if hosts_file:
        with open(hosts_file) as input_:
            host_list = [line.strip() for line in input_]
        env.hosts.extend(host_list)
    with open('output.csv', 'wb') as output:
        writer = csv.writer(output)
        writer.writerow(['HOSTNAME', 'UNAME'])
        with hide('running', 'status'):
            execute(_run, writer)

I run it like this: fab run_uname:test_hosts.txt

My environment is this: RHEL4, Python 2.7.10, Fabric 1.10.2, Paramiko 1.15.2

Thank you!

Felix

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