Pivotal Tracker - The Twelve Factor App

1. The Twelve-Factor App
A Case Study of Pivotal Tracker on Cloud Foundry
Glenn Oppegard
goppegard@pivotal.io

2. Pivotal Tracker
• Development started in 2006, when Pivotal Labs
was starting their Ruby practice
• Ruby 1.8.7 → Ruby 2.1
• Rails 2.3 → Rails 3.2

3. 1. Codebase
• Single codebase
• Many deploys
Image from 12factor.net, MIT License

4. Tracker codebase
• Single bosh release git repository
cf-tracker-release/
src/
cf-tracker/
memcached/
tracker/
tracker-frontend/
tracker-solr-home/

5. 2. Dependencies
• Explicitly declare and isolate dependencies
• Ruby: bundler and Gemfile
• Node: npm and package.json

6. Tracker dependencies
• Bundler
• NPM
• Git sub-modules
• Single artifact containing all dependencies: BOSH
final release tarball: cf-tracker-1.2.1.9.tgz

7. 3. Config
• Resource handles to the database, Memcached,
and other backing services
• Credentials to external services such as Amazon
S3 or Twitter
• Per-deploy values such as the canonical hostname
for the deploy

8. Tracker config
• All config is centralized to a singleton object
• t2config(:smtp_host)
• Reads from environment variables, but also
allows for computed values via Ruby
• Out of 200 config parameters, 25 apply to CF
• Created app_env gem to load static values from
JSON files into environment

9. • Treat backing services as attached resources.
• The code for a twelve-factor app makes no
distinction between local and third party services.
4. Backing Services
Image from 12factor.net, MIT License

10. Tracker services

11. 5. Build, release, run
• Strictly separate build and run stages
• Build: compile code, vendor dependencies, minify
assets
• Release: combine build output with a deploy's
config
• Run.

12. Tracker build stages
• AWS: Continuous Integrations builds "frontend" assets,
stored in S3
• Local: bosh create release
• Strip code not needed on-premise
• Vendor dependencies (bundle install)
• Download frontend from S3
• CF: Ruby buildpack applied to app source

13. 6. Processes
• Execute the app as one or more stateless
processes

14. Tracker processes

15. 7. Port binding
• Export services via port binding

16. 8. Concurrency
• Scale out via the process model
• The unit of currency for a 12-factor
app is the process

17. Tracker Processes
• Web: horizontal scaleout
• Worker: split job-types
• Coming soon: CF Process Types

18. 9. Disposability
• Processes can be killed at any time
• Gracefully handle SIGTERM
• Minimize startup time

19. 10. Dev/prod parity
• Mac vs Linux
• SQLite vs MySQL
• In-memory cache vs Memcached
• Solr
• Coming Soon: Lattice Condenser

20. 11. Logs
• Don't write to disk
• Stream to stdout (or stderr on CF)

21. Tracker logs
• rails_12factor.gem
• rails_stdout_logging.gem

22. 12. Admin processes
• Run admin/management tasks as one-off
processes
• Run tasks in an identical environment to the deploy
(same build and same config → same release)

23. Tracker admin tasks
• Restrict tasks to index 0 of app
• Future: diego one-off processes

24. Credits
• All 12-Factor App diagrams from 12factor.net, MIT
License