psukys-remoto 0.0.31
Execute remote commands or processes. Fork with changes to allow continuous output for remote functions
License: MIT
Keywords: remote

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::

    >>> import logging
    >>> logging.basicConfig(level=logging.DEBUG)
    >>> logger = logging.getLogger('hostname')
    >>> conn = remoto.Connection('hostname', logger=logger)
    >>> run(conn, ['ls', '-a'])
    INFO:hostname:Running command: ls -a
    DEBUG:hostname:.
    DEBUG:hostname:..
    DEBUG:hostname:.bash_history
    DEBUG:hostname:.bash_logout
    DEBUG:hostname:.bash_profile
    DEBUG:hostname:.bashrc
    DEBUG:hostname:.gem
    DEBUG:hostname:.lesshst
    DEBUG:hostname:.pki
    DEBUG:hostname:.puppet
    DEBUG:hostname:.ssh
    DEBUG:hostname:.vim
    DEBUG:hostname:.viminfo

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 = logging.getLogger('myhost')
    >>> conn = Connection('myhost', logger=logger)
    >>> run(conn, ['whoami'])
    INFO:myhost:Running command: whoami
    DEBUG:myhost: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.


Automatic detection for remote connections
------------------------------------------
There is automatic detection for the need to connect remotely (via SSH) or not
that it is infered by the hostname of the current host (vs. the host that is
connecting to).

If the local host has the same as the remote hostname, a local connection (via
`Popen`) will be opened and that will be used instead of `ssh`, and avoiding
the issues of being able to ssh into the same host.

Automatic detection for using `sudo`
------------------------------------
This magical detection can be enabled by using the `detect_sudo` flag in the
`Connection` class. It is disabled by default.

When enabled, it will prefix any command with `sudo`. This is useful for
libraries that need super user permissions and want to avoid passing `sudo`
everywhere, which can be non-trivial if dealing with `root` users that are
connecting via SSH.