Speed up the AWS Elastic Beanstalk deployment of a Ruby on Rails application

At Le Wagon, we use AWS Elastic Beanstalk to host the pedagogic platform used by hundrends of students across the world. This is a Rails 5.1 application using the latest niceties like ActionCable, Webpacker and Sidekiq. If you read my previous article, you know that the command to deploy is:

eb deploy

We have two instances behind a load balancer, with a one-at-a-time deployment strategy. When deploying, a first instance unregisters itself from the Load Balancer and stops serving production traffic. Then the deployer will push the new code and triggers a series of script. If you connect to one of the EC2 instance, you can have a look at them:

eb ssh
ls -l /opt/elasticbeanstalk/hooks/appdeploy/pre/
-rwxr-xr-x 01_unzip.rb
-rwxr-xr-x 02_setup_envvars.sh
-rwxr-xr-x 03_mute_sidekiq.sh
-rwxrwxr-x 101_yarn_setup.sh
-rwxrwxr-x 102_yarn_install.sh
-rwxr-xr-x 10_bundle_install.sh
-rwxr-xr-x 11_asset_compilation.sh
-rwxr-xr-x 12_db_migration.sh
-rwxr-xr-x 13_test_for_puma.sh

The 03_mute_sidekiq.sh, 101_yarn_setup.sh and 102_yarn_install.sh are three tasks I added to support Sidekiq and Webpacker. The other scripts are the one installed by default when you create a new Ruby application on AWS Elastic Beanstalk.

Overall, AWS EB works quite well. But the documentation is scarce / uncomplete / outdated and we are miles away from the speed of a git push heroku master. One reason is that by default, AWS EB won’t cache and re-use gems between two deployments. This means that for every eb deploy, you wait for a full bundle install to run, download every gems and install them. That’s pretty long.

Hopefully, thanks to the hooks sytem, you can write your own. That’s what I did. The idea is to copy the downloaded gems somewhere on the machine, and make sure to re-use that on the next deployments before running the bundle install. You can also use this techniques for assets and reduce the time that rake assets:precompile needs to run.

Here is the script you can take and drop in your .ebextensions folder as a cache.config file:

This script is caching the content of the three following folders:

1. vendor/bundle which is built by bundle install command
2. node_modules which is built by the yarn install command (Webpacker)
3. tmp/cache/assets which stores intermediate Sprocket files built by the rake assets:precompile command

Go ahead and add this to your Rails app hosted on Elastic Beanstalk! We dropped the deployment time on two EC2 machines from 20+ minutes to ~8 minutes!