Rotterdam

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.

• Installation
• Usage
  • Starting up
  • Sending jobs
  • Controlling the master process
  • Controlling the number of consumers
  • Reloading configuration settings
  • Reloading new code
  • Shutting down
• License

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.