adding ability to modify allow_agent variable (which is used in paramiko client) in ParallelSSHClient & SSHClient

[hokadiri]

I ran into an issue lately where I was doing parallel executions on a lot of nodes. By default, in paramiko, ssh-agent is used during the authentication process. I kept getting the lost ssh-agent error below because ssh-agent couldn't handle the load

paramiko.SSHException: lost ssh-agent

To reproduce the issue, try running this ensure you have ssh-agent running. Run the below command

from paramiko import Agent
for i in range(1000):
    agent0=Agent()
    agent1=Agent()
    agent2=Agent()
    ...
    agent98=Agent()
    agent99=Agent()
    agent100=Agent()

Get PID for the ssh-agent socket from the SSH_AUTH_SOCK environment variable

$ echo $SSH_AUTH_SOCK
/tmp/ssh-RFhnS12345/agent.12345

Watch the file descriptors count increase!

$ sudo strace -p 12345 -eselect

And eventually crash with the Exception

SSHException: lost ssh-agent

I want to be able to use username/password OR priv key authentication and I don't want ssh-agent used for authentication. Setting the allow_agent variable in paramiko.SSHClient.connect function to False allows me to disable ssh-agent from being used during authentication.

This PR is to allow us set the allow_agent variable in pssh's ParallelSSHClient & SSHClient and pass it down to paramiko.SSHClient.connect function where its being used

[coveralls]

Coverage increased (+3.3%) to 86.744% when pulling bb9de60 on hokadiri:master into 4356eb1 on pkittenis:master.

[pkittenis]

These indentations are there purposefully as they are used when generating docstrings.

Please revert all indentation changes in this PR.

[hokadiri]

@pkittenis, i've reverted the indentations.

[coveralls]

Coverage increased (+4.4%) to 87.896% when pulling eb83981 on hokadiri:master into 4356eb1 on pkittenis:master.

[pkittenis]

Hi there,

Thanks for the interest and the PR - great investigation.

Made some comments on the diff for review. The new flag functionality also needs a short unittest. Looks great other than that!

Out of interest, what is the pool_size being used and how was the performance?

[hokadiri]

@pkittenis I've added a test case for the allow_agent variable. My pool size was 150. Performance was ok, no noticeable slowness

[coveralls]

Coverage increased (+1.8%) to 85.303% when pulling 7c83a08 on hokadiri:master into 4356eb1 on pkittenis:master.

[pkittenis]

Please revert indentation changes in this file as well - thanks.

[coveralls]

Coverage decreased (-1.6%) to 83.573% when pulling bdccc58 on hokadiri:master into 4356eb1 on pkittenis:master.

[coveralls]

Coverage increased (+3.0%) to 88.184% when pulling b36f468 on hokadiri:master into 4356eb1 on pkittenis:master.

[pkittenis]

Looks great! Thanks again 👍