Improving Rails boot time with Zeus

Zeus improves Rails boot time. Saving seconds is most important when running focused tests:

rspec spec/models/user_spec.rb
rspec spec/models/user_spec.rb:123

Those are times when a tight feedback loop make a meaningful difference.

Install

Install the Zeus gem on your machine:

gem install zeus

Do not include it in your Gemfile. It is an external piece of software.

Set up

Initialize:

zeus init

This will create two files in your Rails app’s directory. Ignore them globally in ~/.gitignore:

custom_plan.rb
zeus.json

Edit zeus.json to include only the tasks for which you’ll use Zeus. Mine looks like this:

{
  "command": "ruby -rubygems -r./custom_plan -eZeus.go",

  "plan": {
    "boot": {
      "default_bundle": {
        "development_environment": {
          "prerake": {"rake": []},
          "console": ["c"],
          "generate": ["g"]
        },
        "test_environment": {
          "test_helper": {"test": ["rspec"]}
        }
      }
    }
  }
}

I remove cucumber in favor of RSpec and Capybara. I remove server in favor of Foreman and Pow.

Force the test environment

In spec/spec_helper.rb, change:

ENV['RAILS_ENV'] ||= 'test'

To:

ENV['RAILS_ENV'] = 'test'

Remove auto-running code

The goal is to run tests in the context of Zeus. So, remove other similar systems.

From the RSpec docs:

> Generally, life is simpler if you just use the rspec command. If you > must use the ruby command, however, you’ll want to do the following:

require 'rspec/autorun'

> This tells RSpec to run your examples.

We don’t need this behavior and can cause bugs when used with Zeus.

Remove either of these lines in spec/spec_helper.rb if they exist:

require 'rspec/autorun'
require 'rspec/autotest'

Remove Spork and Guard

For the same reasons, if you’re using Spork and Guard, delete them from your Gemfile, delete your Guardfile, and delete any related Spork code in spec/spec_helper.rb or spec/support/.

Start Zeus

Zeus will need to be running before you can use its commands:

zeus start

I usually run this, and other long-running processes in a tmux session.

Now, those original commands will have the benefit of Rails boot time in under a second:

zeus rspec spec/models/user_spec.rb
zeus rspec spec/models/user_spec.rb:123

Bonus: run specs from vim

Many of us are running specs directly from vim. If you edit your ~/.vimrc to use Zeus like in this commit, you can run focused specs with:

t

Enjoy!

Written by Dan Croak.