Speeding up Rails deploys to Heroku

Since adding Yarn and Webpacker to a fairly conventional Rails application, my deploy times are taking up to 8 minutes to complete, with an average of roughly 7 minutes per deploy.

Here I am documenting some steps I took to reduce that down below 5 minutes.

The setup

• Deploys are performed by SemaphoreCI once master is green.
• The Rails 5.2 application is running on professional dynos and using the official Ruby and NodeJS buildpacks.
• Migrations are run on each deploy using a release command (release: bundle exec rake db:migrate).

Setting the correct Node and Yarn environments

heroku config:set NPM_CONFIG_PRODUCTION=true YARN_PRODUCTION=true ensures that devDependencies are not installed (source).

Disabling multiple Yarn installs

With multiple buildpacks, yarn install is run 3 times. Adding the following patch to Rakefile ensures this is down to two (source).

Rake::Task['yarn:install'].clear
task 'yarn:install' do
  puts 'Skipping yarn install from Rails'
end

Reducing buildpacks to Ruby only

I’m not sure the NodeJS buildpack is entirely necessary anymore, but it does come with some caching improvements (node_modules folder) that are not in the Ruby buildpack.

Conclusion

With the tweaks above in place, I managed to get deploy times down below 5 minutes. It’s still not like the good old days of <1 minute deploys to Heroku, but it’s definitely an improvement.