Outrigger

Outrigger allows you to tag your migrations so that you can have complete control. This is especially useful for zero downtime deploys to Production environments.

1. Add gem outrigger to your Gemfile and run bundle install
2. Tag migrations like so.

  class PreDeployMigration < ActiveRecord::Migration
    tag :predeploy
  end
  class PostDeployMigration < ActiveRecord::Migration
    tag :super_fun
  end

3. Run only the migrations you want. rake db:migrate:tagged[predeploy] or rake db:migrate:tagged[super_fun]
4. If you need to ensure migrations run in a certain order with regular db:migrate, set up Outrigger.ordered. It can be a hash or a proc that takes a tag; either way it needs to return a sortable value:

Outrigger.ordered = { predeploy: -1, postdeploy: 1 }

This will run predeploys, untagged migrations (implicitly 0), and then postdeploy migrations. Migrations with multiple tags will be looked up by their first tag.

If your application is also using Switchman to manage multiple shards, you'll want the rake db:migrate:tagged task to run against all shards, not just the default shard. To do this, add to a rake task file such as lib/tasks/myapp.rake:

Switchman::Rake.shardify_task('db:migrate:tagged')

Passing multiple tags to db:migrate:tagged means only run migrations that have all of the given tags.

rake db:migrate:tagged[predeploy, dynamodb] means run only migrations tagged with both predeploy and dynamodb. It will not run migrations tagged just predeploy.

Outrigger comes with a custom RuboCop linter that you can add to your project, to verify that all migrations have at least one valid tag.

Put this into your .rubocop.yml.

require:
  - outrigger/cops/migration/tagged

Migration/Tagged:
  Enabled: true
  AllowedTags:
    - predeploy
    - postdeploy

Modify AllowedTags as necessary.

If you use rubocop-rails and have the Rails/ContentTag cop enabled, you may see rubocop errors like the following on your migrations:

Rails/ContentTag: Use tag.predeploy instead of tag(:predeploy).
  tag :predeploy
  ^^^^^^^^^^^^^^

This warning is erroneous, as the rails tag method is really only relevant in controllers and views and is not even in scope for migrations. To silence the warning, add the following to your .rubocop.yml:

Rails/ContentTag:
  Exclude:
    - "**/db/migrate/*" # this cop is for views, not migrations, where it gets confused with outrigger