Automatically clean up Heroku slug

heroku_slug_cleanup.rake

CLEANUP_THRESHOLD = 250 * 1_024_000 # 250 megabytes

# See https://robots.thoughtbot.com/how-to-reduce-a-large-heroku-compiled-slug-size
desc "Clean up the Heroku repo to reduce compiled slug size"
task cleanup: :set_app do
  force = ENV.fetch('FORCE_CLEANUP', false)
  if force || slug_size > CLEANUP_THRESHOLD
    puts "Heroku compiled slug size exceeds 250 MB. Cleaning up the Heroku repo."
    install_heroku_plugin('heroku-repo')
    _execute heroku_command("repo:gc")
    _execute heroku_command("repo:purge_cache")
    puts "Heroku repo clean up complete. Note that the compiled slug size won't be reduced until the next deploy."
  else
    puts "Heroku compiled slug size is less than 250 MB. Not cleaning up. Force a cleanup with FORCE_CLEANUP=1"
  end
end

task :set_app do
  next if defined?(APP)
  if ENV['APP']
    APP = ENV['APP']
    puts "Setting Application to #{APP}"
  else
    $stderr.puts "Expected environment variable APP to be set"
    exit(1)
  end
end

def install_heroku_plugin(plugin)
  if `heroku plugins | grep #{plugin}`.empty?
    puts "Installing Heroku plugin #{plugin}"
    _execute "heroku plugins:install #{plugin}"
  else
    puts "Heroku plugin #{plugin} installed"
  end
end

def slug_size
  app_info['app']['slug_size']
end

def app_info
  @app_info ||= JSON.parse(`#{heroku_command('apps:info --json')}`)
end

def heroku_command(command, opt = { account: ENV['ACCOUNT'] })
  command = "heroku #{command} --app #{APP}"
  command = "#{command} --account #{opt[:account]}" if opt[:account]
  command
end

def _execute(command, exit_on_failure: true)
  print "Executing '#{command}'\n"

  unless system(command)
    puts "Failed to Execute #{command}"
    if exit_on_failure
      code = $CHILD_STATUS.exitstatus
      puts "cowardly exiting with code #{code}"
      exit(code)
    end
  end
end