Circus is a process & socket manager. See https://circus.readthedocs.org
During Django Con, I was asked how to use Circus to run & monitor a Python web application. The documentation has no single page step-by-step tutorial yet, so here goes... this blog post will be integrated into the documentation for the next release.
Circus is tested under Mac OS X and Linux, on the latest Python 2.6 and 2.7. To run a full Circus, you will also need libzmq, libevent & virtualenv.
$ sudo apt-get install libzmq-dev libevent python-virtualenv
Create a virtualenv and install circus, circus-web and chaussette in it
$ virtualenv /tmp/circus $ cd /tmp/circus $ bin/pip install circus $ bin/pip install circus-web $ bin/pip install chaussette
Once this is done, you'll find a plethora of commands in the local bin dir.
Chaussette comes with a default Hello world app, try to run it:
You should be able to visit http://localhost:8080 and see hello world.
Stop Chaussette and add a circus.ini file in the directory containing:
[circus] stats_endpoint = tcp://127.0.0.1:5557 httpd = 1 [watcher:webapp] cmd = bin/chaussette --fd $(circus.sockets.web) numprocesses = 3 use_sockets = True [socket:web] host = 127.0.0.1 port = 9999
This config file tells Circus to bind a socket on port 9999 and run 3 chaussettes workers against it. It also activates the Circus web dashboard and the statistics module.
Save it & run it using circusd:
$ bin/circusd --daemon circus.ini
Now visit http://127.0.0.1:9999, you should see the hello world app.
You can also visit http://localhost:8080/ and enjoy the Circus web dashboard.
Let's use the circusctl shell while the system is running:
$ bin/circusctl circusctl 0.7.1 circusd-stats: active circushttpd: active webapp: active (circusctl)
You get into an interactive shell. Type help to get all commands:
(circusctl) help Documented commands (type help <topic>): ======================================== add get list numprocesses quit rm start stop decr globaloptions listen numwatchers reload set stats dstats incr listsockets options restart signal status Undocumented commands: ====================== EOF help
Let's try basic things. Let's list the web workers processes and add a new one:
(circusctl) list webapp 13712,13713,13714 (circusctl) incr webapp 4 (circusctl) list webapp 13712,13713,13714,13973
Congrats, you've interacted with your Circus! Get off the shell with Ctrl+D and now run circus-top:
This is a top-like command to watch all your processes' memory and CPU usage in real time.
Hit Ctrl+C and now let's quit Circus completely via circus-ctl:
$ bin/circusctl quit ok
You can plug your own WSGI application instead of Chaussette's hello world simply by pointing the application callable.
Chaussette also comes with many backends like Gevent or Meinheld.
Read https://chaussette.readthedocs.org/ for all options.