Make Paramiko backend try to reconnect if connection became closed

[AndreiPashkin]

For example, user might want host to be reverted to a pristine state
before each test run. In that case, the backend would fail, because
before this patch it was simply reused the old closed connection.

[philpep]

Hi, thanks for this PR.

I just wonder what the cost of calling get_transport().is_active() ? Maybe I'll be more efficient to catch the exception (socket.error I presume) and reinit the connection.

[AndreiPashkin]

Exception occurs in different place. I think the cost is not that big to worry about it.

[AndreiPashkin]

Offtop:
I'm trying to install my fork, but pbr throws an error:
Exception: Versioning for this project requires either an sdist tarball, or access to an upstream git repository. Are you sure that git is installed?

And I can't find a solution, maybe you know, how to fix it?

[philpep]

Yes, pbr require a git repo or a sdist (as generated by python setup.py sdist) to get package version.
A solution to install your fork is to use pip. eg.

pip install 'git+https://github.com/AndrewPashkin/testinfra@make_paramiko_backend_not_reuse_collection#egg=testinfra'

[AndreiPashkin]

@philpep, helped! thx 👍

[philpep]

@AndrewPashkin what's your usecase and what version of paramiko are you using ?

I cannot reproduce the issue (instantiate paramiko connection, kill the established connection with conntrack and reuse the paramiko connection), seems paramiko handle this already (version 1.16.0 here).

[philpep]

Ok with tcpkill I get this:

>>> b.run("ls")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "testinfra/backend/paramiko.py", line 84, in run
    chan = self.client.get_transport().open_session()
  File "/home/phil/venvs/testinfra/local/lib/python2.7/site-packages/paramiko/transport.py", line 702, in open_session
    timeout=timeout)
  File "/home/phil/venvs/testinfra/local/lib/python2.7/site-packages/paramiko/transport.py", line 786, in open_channel
    raise SSHException('SSH session not active')
paramiko.ssh_exception.SSHException: SSH session not active

[philpep]

I'm definitely not fan of calling is_active() for each command to run, this could result in a "time to check to time to use" issue. I've implemented an alternative patch in #71 , can you confirm that it solve your issue ? Thanks!

[AndreiPashkin]

@philpep, my use case is that I'm trying to use Vagrant for testing SaltStack formulas and before each test run, my test suite reverts VM to a defined snapshot. After each rollback, SSH connection gets closed.

[philpep]

Closed in flavor of #71