DISQUS Python at 400 500
million visitors Jason Yan David Cramer @jasonyan @zeeg Got feedback? Use hashtag #sckrw Sunday, March 13, 2011

Agenda • What is DISQUS?
• An Overview of the Infrastructure • Iterative Development and Deployment • Why We Love Python Sunday, March 13, 2011

What is DISQUS? dis·cuss •
dĭ-skŭs' We are a comment system with an emphasis on connecting communities http://disqus.com/about/ Sunday, March 13, 2011

Embeddable Comments Sunday, March 13,
2011

A Brief History Sunday, March
13, 2011

Startup-ish • Founded just about
4 years ago • 16 employees, 8 engineers • Tra c increasing 15-20% a month • Flat organizational structure, every engineer is a product manager • Fast turnaround, new feature launches every week (sometimes daily) Sunday, March 13, 2011

Tra c Number of Visitors
500M 375M 250M 125M 0M March 2008 through March 2011 Sunday, March 13, 2011

DjangoCon 2010 • 17,000 requests/
second peak • 450,000 websites • 15 million profiles • 75 million comments • 250 million visitors Sunday, March 13, 2011

Six Months Later • 17,000
requests/ • 25,000 requests/ second peak second peak • 450,000 websites • 700,000 websites • 15 million profiles • 30 million profiles • 75 million • 170 million comments comments • 250 million visitors • 500 million visitors Sunday, March 13, 2011

Six Months Later • September
2010: 250 million uniques • March 2011: 500 million uniques • Handling over 2x the tra c Sunday, March 13, 2011

Six Months Later • September
2010: ~100 servers • March 2011: ~100 servers • Scale diagonally Sunday, March 13, 2011

Scaling Diagonally • We still
rent hardware, so there is no “commodity hardware” • Cheaper to upgrade • Everything is redundant • Partition data where you need to, scale partitions vertically • Upgrade hardware (more RAM, more drives, more cores) • Python apps tend to be CPU bound Sunday, March 13, 2011

Infrastructure • 35% Web Servers
(Apache + mod_wsgi) • 15% Utility Servers (Python scripts, background workers) • 20% Databases (PostgreSQL, Redis, Membase) • 20% Load Balancing / High Availability (HAProxy + Heartbeat) • 10% Caching servers (Memcached, Varnish) • Half of our servers run Python Sunday, March 13, 2011

Python Web Servers • Use
what you’re comfortable with • Apache + mod_wsgi vs nginx + uWSGI Min Avg Max Memory 60.0 mod_wsgi 45.0 30.0 uWSGI 15.0 0 200 400 600 0 mod_wsgi uWSGI req/sec • Bottleneck is in the application Sunday, March 13, 2011

Background Workers • Lots of
tasks that don’t need to be done in web application process: • Crawling URLs • Updating avatars • Email notifications • Analytics • Counters Sunday, March 13, 2011

Background Workers (cont’d) • Most
jobs are I/O bound • Slow external calls • Twitter is slow • Facebook is slow • Could parallelize with multiple processes, but... Sunday, March 13, 2011

Background Workers (cont’d) • Waste
of memory • Use non-blocking I/O • Celery 2.2 adds support for gevent/ eventlet Sunday, March 13, 2011

Monitoring • Application side: Graphite
• Real-time(ish) graphing • Django front-end, Python backend • Etsy’s StatsD proxy to Graphite • UDP (fire and forget) • Batches updates Sunday, March 13, 2011

Monitoring • Track application metrics
• Errors, exceptions • New comments, users, sites, etc. • Anything Sunday, March 13, 2011

Monitoring • Check out Etsy’s
posts: • Measure Anything, Measure Everything http://codeascraft.etsy.com/2011/02/15/measure-anything-measure-everything/ • Tracking Every Release http://codeascraft.etsy.com/2010/12/08/track-every-release/ Sunday, March 13, 2011

What about the code? Sunday,
March 13, 2011

Powered By Django Sunday, March
13, 2011

Which means... • Largest Django-powered
web application • We fork, and even sometimes monkey patch to make it scale to our needs • Fortunately, we don’t have to do too much (Yay, Django!) • Unfortunately, we can’t use the whole of the Django internal components (and if we do, we do it in atypical ways) Sunday, March 13, 2011

Iterative Development Release Early Release
Often Sunday, March 13, 2011

Iterating Quickly • Abstracting our
application environment • Less dependancies locally • Rely on CI for dependency coverage • Heavy use of open source packages • No NIH syndrome • Deploy frequently, 3-7 times a day • Lots of branches, but master is “stable” • Realtime reporting on exceptions, metrics • Our test suite is the main blocker (slow) Sunday, March 13, 2011

Dealing with Deploys Sunday, March
13, 2011

Gargoyle Deploy features to portions
of a user base at a time to ensure smooth, measurable releases Being users of our product, we actively use early versions of features before public release Sunday, March 13, 2011

The Deployment Problem • Make
some changes locally • Run a subset of the test suite • Push your commits • CI server begins running tests • .... Sunday, March 13, 2011

Waiting on the test suite...
Sunday, March 13, 2011

Rinse and Repeat • 30
minutes later tests fail, start over • Finally, deploy to a subset of servers • Open Sentry (our exception logger) • Monitor Graphite • Deploy to 35 servers (~8 minutes) • Full rollback in < 30 seconds Sunday, March 13, 2011

Wait, Sentry? Sunday, March 13,
2011

Testing
Sunday, March 13, 2011

Testing Code • Test suite
takes around 25 minutes usually • “Stuck” with Hudson (or Jenkins) • Most tightly integrated plugins are geared towards Java developers • Which framework do we use? • unittest(2), nose, doctests, LETTUCE? • We use unittest and nose • Need to report code coverage, speed of tests, pylint (or pyflakes) Sunday, March 13, 2011

We Love Python Sunday, March
13, 2011

Love-ish • Many of us
started with PHP or Rails • Clean syntax, clear standards • All languages need PEP8.py and PyFlakes • Interpreted, fast... enough • Very easy to learn • We all started by learning Django first, then Python Sunday, March 13, 2011

Haters Gonna Hate If you
could choose one thing in Python to hate on... Sunday, March 13, 2011

Better package management Sunday, March
13, 2011

What can we do? •
Too many forks, too many frameworks • We need less clones, and more combined e ort • Improving existing Python solutions • More Python solutions for existing products Sunday, March 13, 2011

Python Rocks! Sunday, March 13,
2011

DISQUS Questions? psst, we’re hiring
jobs@disqus.com Sunday, March 13, 2011

References • Sentry (our exception
tracking tool) http://github.com/dcramer/django-sentry • Gargoyle (feature switches) https://github.com/disqus/gargoyle • Django DB Utils (collection of db helpers for Django) https://github.com/disqus/django-db-utils • Jenkins CI http://jenkins-ci.org/ code.disqus.com Sunday, March 13, 2011