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Deploying, at an Unusual Scale

Deploying, at an Unusual Scale

A talk I gave at DjangoCon Europe 2011, about Epio's internal architecture at that point.

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Andrew Godwin

October 22, 2011
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Transcript

  1. Deploying, At An Unusual Scale Andrew Godwin http://www.flickr.com/photos/whiskeytango/1431343034/ @andrewgodwin

  2. Hi, I'm Andrew. Serial Python developer Django core committer Co-founder

    of ep.io
  3. Hi, I'm Andrew. Serial Python developer Django core committer Co-founder

    of ep.io Occasional fast talker
  4. ""Andrew speaks English like a machine gun speaks bullets."" Reinout

    van Rees
  5. We're ep.io Python Platform-as-a-Service Easy deployment, easy upgrades PostgreSQL, Redis,

    Celery, and more
  6. Why am I here? Our Architecture How we deploy Django

    How varied Django deployments are
  7. Our Architecture

  8. Balancer Runner Runner Runner App 1 App 2 App 3

    App 2 App 4 App 1 Databases File Storage Balancer
  9. Oh My God, It's Full of Pairs Everything is redundant

    Distributed programming is Hard
  10. Hardware Real colo'd machines Linode EC2 (pretty unreliable) (pretty reliable)

    (pretty reliable) IPv6 (as much as we can)
  11. ØMQ We used to use Redis Everything now on ZeroMQ

    Eliminates SPOF* * Single Point Of Failure. What a pointless acronym.
  12. ØMQ Usage Redundant location-resolvers (Nexus) REQ/XREP for control messages PUSH/PULL

    for stats, logs PUB/SUB for heartbeats, locking
  13. Runners Unsurprisingly, these run the code SquashFS filesystem images Virtualenvs

    per app UID & permission isolation, more coming
  14. Logging/Stats All done asynchronously using ØMQ Logs to filesystem (chunked

    files) Stats to PostgreSQL database, for now
  15. Loadbalancers Intercept all incoming HTTP requests Look up hostname (or

    suffix) HTTP 1.1 compliant
  16. Databases Shared (only for PostgreSQL) Dedicated (uses Runner framework) PostgreSQL

    9, damnit
  17. Django in the backend We use the ORM extensively Annoying

    settings fiddling in __init__
  18. www.ep.io Runs on ep.io, just like any other app* Provides

    JSON API, web UI * Well not quite - App ID 0 is special - but we're working on it
  19. WSGI It's a standard, right?

  20. WSGI It's a standard, right? Well, yes, and it works

    fine, but it's not enough for serving a Python app
  21. Static Files CSS, images, JavaScript, etc. Needs a URL and

    a directory path
  22. Python & Dependencies Mostly filled by pip/buildout/etc packaging apparently allows

    version spec
  23. Deploying Django It makes things consistent, right?

  24. Settings Layouts Vanilla settings.py local_settings.py configs/HOSTNAME.py Many others...

  25. Python Paths Project-level imports App-level imports apps/ directories

  26. Databases If it's SQL, it's PostgreSQL Redis for key-value, MongoDB

    soon Some things assume a safe network
  27. HA (High Availability) Not terribly easy with shared DBs PostgreSQL

    9's sensible warm standby Redis has SLAVEOF Possibly use DRBD for general solution
  28. Backups High Availability is NOT a backup btrfs for consistent

    snapshotting Archived remote syncs No access to backups from servers
  29. Migrations No solution yet for migration/code sync We're working on

    it...
  30. Web serving It's not like it's important or anything

  31. gunicorn Small and lightweight Supports long-running requests Pretty stable

  32. nginx Even more lightweight Extremely fast Really, really stable

  33. The Load Balancer Used to be HAProxy Rewritten to custom

    Python daemon eventlet used for high throughput Can't use nginx, no HTTP 1.1 for backends
  34. Celery See: Yesterday's Talk Slightly tricky to run many We

    use Redis as the backend
  35. Management Commands First off, run as subprocess Then, a custom

    PTY module Now, run as pty-wrapping subprocesses
  36. Some General Advice If you're crazy enough to do this

  37. Messaging's Not Enough Having a state to check is handy

  38. Why run one, when you can run two for twice

    the price? Redundancy is good. Double redundancy is better.
  39. Always expect the worst Hope you never have to deal

    with it.
  40. The more backups, the better. Make sure you have historical

    ones, too.
  41. Django is very flexible Sometimes a little too flexible...

  42. Your real problems will emerge later Don't over-optimise up front

    for everything
  43. Questions? Andrew Godwin andrew@ep.io @andrewgodwin