rotterdam

Rotterdam

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Rotterdam is an asynchronous job queue system written in Python with a dab of Lua, designed with simplicty and ease of use in mind with as few dependencies as possible.

It uses Redis_ as its datastore and is heavily inspired by the Unicorn_ and Gunicorn_ master/worker process model.

.. contents:: :local:

Installation

Rotterdam is available via pypi, installing for clients is as easy as::

pip install rotterdam

To use the server scripts, install the "server" subproject::

pip install rotterdam[server]

Usage

Make sure to have a redis instance version 2.6 or newer at the location specified in your config file under the arbiter section. See the example.cfg file for an example.

Starting up

To start the rotterdam server, run the ``rotterdam`` executable and pass in
the location of a config file (an example.cfg is included in this here repo)::

    [ ~ ] $ rotterdam example.cfg
    INFO:rotterdam.master:Starting master (52174)
    INFO:rotterdam.master:Listening on port 8765
    INFO:rotterdam.master:Starting up consumer
    INFO:rotterdam.master:Starting up consumer

Sending jobs

All a client program has to do is instantiate a Rotterdam class with the proper host and port and call enqueue::

from rotterdam import Rotterdam

client = Rotterdam("localhost")  # default port is 8765

client.enqueue("rotterdam.example:some_job", "thingy", "guy", foo="bar")
client.enqueue("rotterdam.example:some_job", "derp", "hork", foo="bazz")

The first argument to enqueue can either be an instance of a function, or a string with the full namespace of the function to be run.

In this example, the job is a simple function that prints out its own arguments::

import time

def some_job(arg1, arg2, foo=None):
    time.sleep(2)
    print "arg1: %s" % arg1
    print "arg2: %s" % arg2
    print "foo: %s" % foo

So once the client program is run the rotterdam process will print out the args on its end::

arg1: derp
arg2: hork
foo: bazz
arg1: thingy
arg2: guy
foo: bar

Note that since it's jobs are executed concurrently with consumer processes they don't necessarily execute in the same order the client sends them.

Controlling the master process

Rotterdam uses inter-process communcation (IPC) signals for most tasks so that
the master/worker processes can chug along the whole time without needed to
be restarted.  The ``rotterdamctl`` program is a handy utility for sending
the proper signals to the proper process.  This program also takes the location
of a config file as the first argument.  Make sure to use the same config file
as the rotterdam process you want to control!

Controlling the number of consumers

To add a consumer to the existing rotterdam processes, pass the expand command to rotterdamctl.::

[ ~ ] $ rotterdamctl example.cfg expand

The master processes will log that a new consumer is added::

INFO:rotterdam.master:Upping number of consumers to 3
INFO:rotterdam.master:Starting up consumer

Contracting the number of consumers is a similiar process, but with the contract command::

[ ~ ] $ rotterdamctl example.cfg contract

INFO:rotterdam.master:Contracting number of consumers to 2
INFO:rotterdam.master:Consumer exiting

Reloading configuration settings

The rotterdam master process has a facility for reloading its config file
on-the-fly so no work is lost. It is invoked with the ``reload`` command to
``rotterdamctl``.::

    [ ~ ] $ rotterdamctl example.cfg reload

The master process will then re-read the config file and signal each worker
process to wrap up whatever it's doing while at the same time spawning new
worker processes based on the new config.::

    INFO:rotterdam.master:Reloading config
    INFO:rotterdam.master:Starting up consumer
    INFO:rotterdam.master:Starting up consumer
    INFO:rotterdam.master:Consumer exiting
    INFO:rotterdam.master:Consumer exiting


Reloading new code
~~~~~~~~~~~~~~~~~~
Naturally, rotterdam only knows of the jobs available to its python runtime.
What to do when you update the code to have shiny new jobs, but you don't want
to shut down or pause any work while updating?  For this case there's the
``relaunch`` command::

    [ ~ ] $ rotteramctl example.cfg relaunch

The master process will spawn a new master with the same arguments it was invoked
with and passes along the listening socket's file descriptor.::

    INFO:rotterdam.master:Winding down old master
    INFO:rotterdam.master:Starting master (52580)
    INFO:rotterdam.master:Listening on port 8765
    INFO:rotterdam.master:Starting up consumer
    INFO:rotterdam.master:Starting up consumer
    INFO:rotterdam.master:Consumer exiting
    INFO:rotterdam.master:Consumer exiting
    [ ~ ] $

Once the new master is up and running, the old master process signals its child
worker processes to wrap up what they're doing and shuts itself down while the
new master processes chugs along and accepts data on the same socket but with
freshly-loaded python code.

Shutting down
~~~~~~~~~~~~~
Stopping rotterdam is done via the ``stop`` command::

    [ ~ ] $ rotterdamctl example.cfg stop

    INFO:rotterdam.master:Winding down master
    INFO:rotterdam.master:Consumer exiting
    INFO:rotterdam.master:Consumer exiting

License
-------

\(c\) 2013-2015 William Glass

Rotterdam licensed under the terms of the MIT license.  See the LICENSE_ file
for more details.


.. _Redis: http://redis.io/
.. _Unicorn: http://unicorn.bogomips.org
.. _Gunicorn: https://github.com/benoitc/gunicorn
.. _LICENSE: https://github.com/wglass/rotterdam/blob/master/README.md