Continuous Deployment at Disqus (Pylons Minicon)

DISQUS
Continuous Deployment Everything

David Cramer
@zeeg

Friday, April 29, 2011

Disclaimer: We don’t use Pylons


Continuous Deployment

Shipping new code as soon
as it’s ready

(It’s really just super awesome buildbots)


Workﬂow

1. Developer commits code
2. CI server runs tests automatically
2.1.Build passes, code deploys
2.2.Build fails, block deploy
3. Developer tests feature on production


Pros Cons

• Develop features • Culture Shock
incrementally • Stability depends on
• Release frequently test coverage
• Less QA! (maybe) • Initial time
investment

We mostly just care about iteration and stability


Painless Development


Development

• Production > Staging > CI > Dev
• Automate testing of complicated
processes and architecture
• Simple is arguably better than complete
• Especially for local development
• python setup.py {develop,test}
• Use Puppet/Chef or build a simple
bootstrap.{py,sh}


Production Staging
• PostgreSQL • PostgreSQL
• Memcache • Memcache
• Redis • Redis
• Solr • Solr
• Apache • Apache
• Nginx • Nginx
• RabbitMQ • RabbitMQ

CI Server Macbook

• Memcache • PostgreSQL
• PostgreSQL • Apache
• Redis • Memcache
• Solr • Redis
• Apache • Solr
• Nginx • Nginx
• RabbitMQ • RabbitMQ


Bootstrapping Local

• Simplify local setup
• git clone dcramer@disqus:disqus.git
• python setup.py develop
• python manage.py runserver

• Need to test dependancies?
• virtualbox + vagrant up


“Under Construction”

• Iterate quickly by hiding features
• Early adopters are free QA

from gargoyle import gargoyle

def my_view(request):
if gargoyle.is_active('awesome', request):
return 'new happy version :D'
else:
return 'old sad version :('


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


Integration
(or as we like to call it)


Integration is Required

Deploy only when things wont break


Reporting is Critical


CI Requirements

✓ Developers must know when they’ve
broken something
✓ IRC, Email, IM
✓ Support proper reporting
✓ XUnit, Pylint, Coverage.py
✓ Painless setup
✓ apt-get install jenkins


Shortcomings

• False positives lower awareness
• Reporting isn't accurate
• Services fail
• Bad Tests
• Not enough code coverage
• Regressions on untested code
• Test suite takes too long
• Integration tests vs Unit tests


Fixing False Positives

• Re-run tests several times on a failure
• Report continually failing tests
• Fix continually failing tests
• Rely less on 3rd parties
• Mock/Dingus


Maintaining Coverage

• Raise awareness with reporting
• Fail/alert when coverage drops on a build
• Commit tests with code
• Drive it into your culture


Speeding Up Tests

• Write true unit tests
• vs slower integration tests
• Mock 3rd party APIs
• Distributed and parallel testing
• http://github.com/disqus/mule


Mule

• Unstable (we’re working on it)
• Mostly Django right now
• Generic interfaces for unittest2
• Works with multi-processing and Celery
• More complex than normal Celery usage
• Full XUnit integration
• Simple workﬂow
• mule test --runner="python manage.py
mule --worker $TEST"


Deploy (ﬁnally)


How DISQUS Does It

• Incremental deploy with Fabric
• Drop server from pool
• Pull in requirements on each server
• Isolated virtualenv’s built on each server
• Push server back online


Challenges

• PyPi works on server A, but not B
• Scale, or lack of
• CPU cost per server
• Schema changes, data model changes
• Backwards compatibility


PyPi is Down

• http://github.com/disqus/chishop


Help, we have 100 servers!

• Incremental (ours) vs Fanout
• Push vs Pull
• Twitter uses BitTorrent
• Isolation vs Packaging (Complexity)


SQL Schema Changes
1. Add column (NULLable)
2. Add app code to ﬁll column
3. Deploy
4. Backﬁll column
5. Add app code to read column
6. Deploy

Cached Data Changes

• Have a global version number
• Have a data model cache version
• maybe md5(cls.__dict__)?


DISQUS
Questions?

psst, we’re hiring
jobs@disqus.com


References

• Mule (distributed test runner)
http://github.com/disqus/mule
• Gargoyle (feature switches)
https://github.com/disqus/gargoyle
• Jenkins CI
http://jenkins-ci.org/

code.disqus.com

Continuous Deployment at Disqus (Pylons Minicon)

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