As you know from my previous post, I recently deleted LinkPeek.com and after struggling to get it back online, I vowed to start utilizing configuration management. During this exercise, I noticed that the architecture I use in production seems overly complicated.
The current production deployment stack:
- Nginx listen on 80/443 proxy upstream 9901/9902
- Upstart => Supervisord => Cherrypy/Paste listen on 9901/9902
Each of these services and processes have their own configuration files which must work together. Upstart needs to know the location of Supervisord's configuration files. Supervisord needs to know the location of Cherrypy/PasteDeploy's configuration files. Supervisord also must bring up a specified number of worker processes who listen on a pool of ports. Nginx needs to proxy upstream to that pool of worker ports.
This architecture seems difficult to automate because of the numerous places errors may sneak in. I started researching an alternative architecture and stumbled upon Nicholas Piel's Benchmark of Python Web Servers. The graphs Nicholas compiled allowed me to narrow down a list of potential replacements.
I chose to review uWSGI first because it was a top contender on every chart. After briefly testing uWSGI, I halted my explorations and selected it as the winner. I know you probably feel that was a premature decision but uWSGI fit what I was looking for.
The new simplified stack:
- Nginx listen on 80/443 proxy upstream 5200
- Upstart => uWSGI listen on 5200
The uWSGI server possesses great performance out-of-the-box but also presents many options for fine tuning. These options may be specified either directly in the Upstart script using flags or in a configuration file (like a Pyramid .ini). Either way, the stack uses less files, less processes, and less complexity then the original architecture. For LinkPeek deployments I decided to place all uWSGI related configuration directly in the Upstart script which I embedded below:
linkpeek/weblinkpeek.conf | Upstart for starting uWSGI
description "Start the uWSGI master for the LinkPeek WEB" start on runlevel  stop on runlevel [!2345] respawn # run service as linkpeek user setuid linkpeek setgid linkpeek # uWSGI command to execute and treat as a daemon exec /path/to/linkpeek/web/env/bin/uwsgi --master --processes=4 --http=127.0.0.1:5200 --die-on-term --logto2=/path/to/linkpeek/web/uwsgi.log --virtualenv=/path/to/linkpeek/web/env --ini-paste=/path/to/linkpeek/web/linkpeek/production.ini
The web application is now daemonized and listening on port 5200 with 4 workers. I leave implementing the Nginx front end to the reader.
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