remoto

A very simplistic remote-command-executor using ssh and Python in the remote end.

All the heavy lifting is done by execnet, while this minimal API provides the bare minimum to handle easy logging and connections from the remote end.

remoto is a bit opinionated as it was conceived to replace helpers and remote utilities for ceph-deploy a tool to run remote commands to configure and setup the distributed file system Ceph.

Example Usage

The usage aims to be extremely straightforward, with a very minimal set of helpers and utilities for remote processes and logging output.

The most basic example will use the run helper to execute a command on the remote end. It does require a logging object, which needs to be one that, at the very least, has both error and debug. Those are called for stderr and stdout respectively.

This is how it would look with a basic logger passed in:

>>> logger = logging.getLogger('hostname')
>>> conn = remoto.Connection('hostname', logger=logger)
>>> run(conn, ['ls', '-a'])
2013-09-07 15:32:06,662 [hostname][DEBUG] .
2013-09-07 15:32:06,662 [hostname][DEBUG] ..
2013-09-07 15:32:06,662 [hostname][DEBUG] .bash_history
2013-09-07 15:32:06,662 [hostname][DEBUG] .bash_logout
2013-09-07 15:32:06,662 [hostname][DEBUG] .bashrc
2013-09-07 15:32:06,662 [hostname][DEBUG] .cache
2013-09-07 15:32:06,664 [hostname][DEBUG] .profile
2013-09-07 15:32:06,664 [hostname][DEBUG] .ssh

The run helper will display the stderr and stdout as ERROR and DEBUG respectively.

For other types of usage (like checking exit status codes, or raising upon them) remoto does provide them too.

Remote Commands

process.run

Calling remote commands can be done in a few different ways. The most simple one is with process.run:

>>> from remoto.process import run
>>> from remoto import Connection
>>> logger = my_logging_setup('hostname')
>>> conn = Connection('hostname')
>>> run(conn, ['whoami'])
2013-09-07 15:32:06,664 [hostname][DEBUG] root

Note however, that you are not capturing results or information from the remote end. The intention here is only to be able to run a command and log its output. It is a fire and forget call.

process.check

This callable, allows the caller to deal with the stderr, stdout and exit code. It returns it in a 3 item tuple:

>>> from remoto.process import check
>>> check(conn, ['ls', '/nonexistent/path'])
([], ['ls: cannot access /nonexistent/path: No such file or directory'], 2)

Note that the stdout and stderr items are returned as lists with the \n characters removed.

This is useful if you need to process the information back locally, as opposed to just firing and forgetting (while logging, like process.run).

Remote Functions

To execute remote functions (ideally) you would need to define them in a module and add the following to the end of that module:

if __name__ == '__channelexec__':
    for item in channel:
        channel.send(eval(item))

If you had a function in a module named foo that looks like this:

import os

def listdir(path):
    return os.listdir(path)

To be able to execute that listdir function remotely you would need to pass the module to the connection object and then call that function:

>>> import foo
>>> conn = Connection('hostname')
>>> remote_foo = conn.import_module(foo)
>>> remote_foo.listdir('.')
['.bash_logout',
 '.profile',
 '.veewee_version',
 '.lesshst',
 'python',
 '.vbox_version',
 'ceph',
 '.cache',
 '.ssh']

Note that functions to be executed remotely cannot accept objects as arguments, just normal Python data structures, like tuples, lists and dictionaries. Also safe to use are ints and strings.