A Big Refactoring!

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We've just rolled out a big refactoring to the Travis CI application (i.e. the server app which runs on Heroku) that we've been working on over the last four weeks.

This refactoring was quite far-reaching and even though we've tried hard to make sure everything works fine there may be glitches and bugs that we've overlooked.

Why?

The motivation behind all of this work was quite manifold. Maybe the best summary is that our previous domain model still had the very basic design from its original spike. But here are some more details. We wanted to achieve the following things:

  • Split up the monster Build model into more fine-grained classes for more clarity
  • Move to a statemachine-like pattern for more explicitly reflecting various state changes that happen across various models
  • Lay better grounds for the long planned move to AMQP (communication with the workers)
  • Lay better grounds for the long planned move Sproutcore (reimplementation of the JS client)
  • Improve test coverage and move to RSpec (for unifying test technologies and a slightly lower barrier for new devs)
  • Generally clean up both model and test code.

One major intention was to generally clean up our codebase, complete and improve the test suite and make the model design more readable. Another was to split up the former Build model which had grown into a huge tangled monster. And while we were at it we also wanted to better communicate the fact that the domain model is very much about about triggering state changes through various events and messages.

You can find more information about the new domain model design in this document. Some of the details outlined there haven't been implemented, yet. E.g. the Build model does not have the mentioned errored and cancelled states, the Task::Test does not have cloned and installed states ... simply because the worker does not support triggering these, yet. These things will probably be added in a later stage.

When we reviewed common Ruby statemachine implementations we found none of them do what we needed, so we came up with our own brand of it: simple_states may or may not useful for your own use case but it does exactly what we need in Travis CI and nothing more.

Another gem that has been implemented in the course of this refactoring is data_migrations. We had quite a bunch of columns to migrate from the builds table to various other tables (such as commits, requests, tasks) and it seemed easier to come up with a simple DSL for that than writing all these queries by hand.

Also, we're now using hashr in the application, too (for Travis.config, specifically). We've used it in the worker code before and it worked pretty well.

In other news

Over the last month we have extracted a small project that we use to develop our Chef cookbooks and added the following tools to the VM infrastructure:

  • kerl to support Erlang with testing against multiple OTP releases
  • leiningen 1.6 for Clojure projects
  • sbt 0.10 for Scala projects
  • Thinking Sphinx 0.9.9, 1.10 and 2.0. Riddle and Thinking Sphinx are now hosted on Travis.
  • RabbitMQ now installs HTTP API plugin

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