capistrano + goose

deploy.rb

set :conditionally_migrate, fetch(:conditionally_migrate, false)
set :migration_role, fetch(:migration_role, :db)
set :migration_servers, -> { primary(fetch(:migration_role)) }

namespace :deploy do
  task :set_app_env do
    set :app_env, (fetch(:app_env) || fetch(:stage))
  end

  desc 'Runs goose up if migrations are set'
  task migrate: [:set_app_env] do
    on fetch(:migration_servers) do
      conditionally_migrate = fetch(:conditionally_migrate)
      info '[deploy:migrate] Checking changes in db' if conditionally_migrate
      if conditionally_migrate && test(:diff, "-qr #{release_path}/db #{current_path}/db")
        info '[deploy:migrate] Skip `deploy:migrate` (nothing changed in db)'
      else
        info '[deploy:migrate] Run `goose up`'
        # NOTE: We access instance variable since the accessor was only added recently. Once capistrano-rails depends on rake 11+, we can revert the following line
        invoke :'deploy:migrating' unless Rake::Task[:'deploy:migrating'].instance_variable_get(:@already_invoked)
      end
    end
  end

  desc 'Runs goose up'
  task migrating: [:set_app_env] do
    on fetch(:migration_servers) do
      within release_path do
        with app_env: fetch(:app_env) do
          execute :goose, "-env #{fetch(:app_env)} up"
        end
      end
    end
  end

  after 'deploy:updated', 'deploy:migrate'
end