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The Peris of Writing a PaaS
Andrew Godwin
May 10, 2011
Programming
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The Peris of Writing a PaaS
A talk I gave at London Devops in May of 2011.
Andrew Godwin
May 10, 2011
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Transcript
The Perils of Writing a PaaS Andrew Godwin http://www.flickr.com/photos/jannem/2719976702/
Hi, I'm Andrew. Serial Python developer Django core committer Sysadmin
by night
We're ep.io Python Platform-as-a-Service Utility billing PostgreSQL, Redis, Celery, and
more
We built a… prototype. Me and Ben Firshman Three or
four days' hacking at DjangoCon Ran code, had simple deployment
The last 10%... A month or two of hibernation Went
part-time in December Private beta since February Public launch later this year
Why? Why not?
Why? Why not? Lack of good solutions Strong, technical team
Writing backend code is fun
It's a challenge We're still a closed beta 300+ apps,
on 4 servers Some people just have crazy code Security, security, security
Our Architecture
ep.io Cloud Request Sugar XML Response Code Magic
Balancer Runner Runner Runner App 1 App 2 App 3
App 2 App 4 App 1 Databases File Storage
Load Balancer Started with HaProxy Moved to custom Python loadbalancer
Still needs refinement
Runners Daemon on each machine Nginx + gunicorn for each
app instance Output captured, CPU time measured
Coordinator Analyses whole system Juggles apps between servers Detects dead
servers
PostgreSQL Normal PostgreSQL 9 install Daemon to read query logs,
make users
Redis Custom Redis loadbalancer/manager Starts processes on demand Handles multi-user
security
Upload Receiver SSH endpoint for git, hg, commands Wraps VCSs,
extracts uploaded files Creates filesystem images
Other Services Log aggregation UID assignment Calculate costs
Statistics Queued in Redis Consumed asynchronously Currently stored in Redis,
changing soon Graphed and profiled
Configuration Management Puppet for the simpler stuff Daemons handle complex
stuff Don't try to reinvent the wheel
Monitoring Nagios SaaS monitoring Nagios Emails, texts, pager Several custom
checks
Backups Currently just rdiff-backup Moving to btrfs snapshots + DRBD
HA is not a backup solution
Perils
Initial bad design (To be fair, it was a prototype)
Networks really aren't reliable (Well, EC2's, at least.)
Memory pressure is bad (Prepare to have a fallback. And
another.)
Raw file handles are… fun. (As is the PTY subsystem.
Be very careful.)
Write just enough automation (If a server dies, I now
just go and get a drink)
HaProxy doesn't like 500+ backends (it's not exactly common)
Single redundancy is only so good (and remember, HA is
not backups!)
Future Perils
Payment (Already underway, still hard)
Oversized Sites (we need to get a lot bigger first)
European Servers (people really do want them)
More Databases (how on earth do you measure MongoDB use?)
More Languages (easy to get it working, hard to polish)
The Potential Big Outage (quite useful as a motivational tool)
Thank you. Andrew Godwin @andrewgodwin andrew@ep.io