The Peris of Writing a PaaS

Transcript

1. 1.

   The Perils of Writing a PaaS Andrew Godwin http://www.flickr.com/photos/jannem/2719976702/

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   Hi, I'm Andrew. Serial Python developer Django core committer Sysadmin

   by night
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   We're ep.io Python Platform-as-a-Service Utility billing PostgreSQL, Redis, Celery, and

   more
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   We built a… prototype. Me and Ben Firshman Three or

   four days' hacking at DjangoCon Ran code, had simple deployment
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   The last 10%... A month or two of hibernation Went

   part-time in December Private beta since February Public launch later this year
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   Why? Why not?

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   Why? Why not? Lack of good solutions Strong, technical team

   Writing backend code is fun
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   It's a challenge We're still a closed beta 300+ apps,

   on 4 servers Some people just have crazy code Security, security, security
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   Our Architecture

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    ep.io Cloud Request Sugar XML Response Code Magic

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    Balancer Runner Runner Runner App 1 App 2 App 3

    App 2 App 4 App 1 Databases File Storage
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    Load Balancer Started with HaProxy Moved to custom Python loadbalancer

    Still needs refinement
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    Runners Daemon on each machine Nginx + gunicorn for each

    app instance Output captured, CPU time measured
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    Coordinator Analyses whole system Juggles apps between servers Detects dead

    servers
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    PostgreSQL Normal PostgreSQL 9 install Daemon to read query logs,

    make users
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    Redis Custom Redis loadbalancer/manager Starts processes on demand Handles multi-user

    security
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    Upload Receiver SSH endpoint for git, hg, commands Wraps VCSs,

    extracts uploaded files Creates filesystem images
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    Other Services Log aggregation UID assignment Calculate costs

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    Statistics Queued in Redis Consumed asynchronously Currently stored in Redis,

    changing soon Graphed and profiled
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    Configuration Management Puppet for the simpler stuff Daemons handle complex

    stuff Don't try to reinvent the wheel
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    Monitoring Nagios SaaS monitoring Nagios Emails, texts, pager Several custom

    checks
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    Backups Currently just rdiff-backup Moving to btrfs snapshots + DRBD

    HA is not a backup solution
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    Perils

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    Initial bad design (To be fair, it was a prototype)

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    Networks really aren't reliable (Well, EC2's, at least.)

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    Memory pressure is bad (Prepare to have a fallback. And

    another.)
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    Raw file handles are… fun. (As is the PTY subsystem.

    Be very careful.)
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    Write just enough automation (If a server dies, I now

    just go and get a drink)
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    HaProxy doesn't like 500+ backends (it's not exactly common)

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    Single redundancy is only so good (and remember, HA is

    not backups!)
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    Future Perils

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    Payment (Already underway, still hard)

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    Oversized Sites (we need to get a lot bigger first)

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    European Servers (people really do want them)

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    More Databases (how on earth do you measure MongoDB use?)

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    More Languages (easy to get it working, hard to polish)

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    The Potential Big Outage (quite useful as a motivational tool)

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    Thank you. Andrew Godwin @andrewgodwin andrew@ep.io