Advanced Heroku Settings For Rails

Deploying your Rails app to Heroku is generally straight forward, however there's a lot of additional configuration needed to make sure things scalable and memory efficient. The following are some tips and recommendations on setting up your Rails app on Heroku.

Note, before setting these environment variables or adding the buildpacks, make sure you’ve first deployed your Rails app to Heroku. Adding these variables or buildpacks before can mess up the initial setup process.

Jemalloc Buildpack

jemalloc is a general purpose malloc implementation that works to avoid memory fragmentation in multithreaded applications. This buildpack makes it easy to install and use jemalloc on Heroku and compatible platforms.

You can add the jemalloc buildpack by running the following.

heroku buildpacks:add --index 1 https://github.com/gaffneyc/heroku-buildpack-jemalloc.git

Next you'll need to set the JEMALLOC_ENABLED environment variable on Heroku.

heroku config:set JEMALLOC_ENABLED=true

More information at elements.heroku.com/buildpacks/gaffneyc/heroku-buildpack-jemalloc.

Postgres Bouncer Buildpack

This is a Heroku buildpack that allows one to run pgbouncer in a dyno alongside application code. The primary use of this buildpack is to allow for transaction pooling of PostgreSQL database connections among multiple workers in a dyno.

Add the heroku-buildpack-pgbouncer buildpack by running.

heroku buildpacks:add https://github.com/heroku/heroku-buildpack-pgbouncer

Next, either add or update your Procfile, the below is assuming you are using Sidekiq.

web: bin/start-pgbouncer-stunnel bundle exec puma -C config/puma.rb
worker: bundle exec sidekiq -C config/sidekiq.yml

Important, in your config/database.yml ensure the following flags are set in your production environment.

advisory_locks: false
prepared_statements: false

More information at elements.heroku.com/buildpacks/heroku/heroku-buildpack-pgbouncer.

Set Rails Master Key

If you are using config/credentials.yml.enc, you'll need to set the RAILS_MASTER_KEY environment variable.

heroku config:set RAILS_MASTER_KEY=`cat config/master.key`

Change Service Timeout

You can specify request timeout by setting the RACK_TIMEOUT_SERVICE_TIMEOUT environment variable.

heroku config:set RACK_TIMEOUT_SERVICE_TIMEOUT=20

More information at devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server#timeout.

Set Sensible Defaults

If a Ruby application has the configuration variable SENSIBLE_DEFAULTS set, then the configuration variable WEB_CONCURRENCY will be defaulted to a value based on the dyno size.

heroku config:set SENSIBLE_DEFAULTS=enabled

More information at devcenter.heroku.com/changelog-items/618.

Enable Preboot

Preboot changes the standard dyno start behavior for web dynos. Instead of stopping the existing set of web dynos before starting the new ones, preboot ensures that the new web dynos are started (and receive traffic) before the existing ones are terminated. This can contribute to zero downtime deployments.

You can enable preboot functionality by running the following.

heroku features:enable preboot

More information at devcenter.heroku.com/articles/preboot.

Enable Runtime Heroku Metrics

To provide additional insights into memory health we offer optional language-specific runtime metrics. JVM, Go (public beta), Node.js (public beta), and Ruby (public beta) are currently supported.

heroku labs:enable "runtime-heroku-metrics"

More information at devcenter.heroku.com/articles/language-runtime-metrics.

Enable Ruby Language Metrics

To provide more visibility into the Ruby runtime, the Ruby language metrics feature surfaces additional language-specific time series metrics within Application Metrics. Ruby metrics include free and allocated heap object counts and number of free memory slots.

heroku labs:enable "ruby-language-metrics"

More information at devcenter.heroku.com/articles/language-runtime-metrics-ruby.

Set Ruby GC heap Growth Factor

When it comes to memory utilization you can control how fast Ruby allocates memory by setting RUBY_GC_HEAP_GROWTH_FACTOR. This value is different for different versions of Ruby. To understand how it works it is helpful to first understand how Ruby uses memory.

heroku config:set RUBY_GC_HEAP_GROWTH_FACTOR=1.03

More information at devcenter.heroku.com/articles/ruby-memory-use#gc-tuning.

Rails Autoscale Add-on

RailsAutoscale is one of the must have add-ons for Heroku. It lets you scale your web and worker dynos up and down based on queue time. So besides helping your application scale, it can also save you a lot or money.

More information at elements.heroku.com/addons/rails-autoscale.

Scout APM Add-on

Scout APM is another must have add-on for Heroku. It helps find N+1 queries, slow database queries, memory bloat and more.

More information at elements.heroku.com/addons/scout.

Choosing Your Dynos

I highly recommend you read How many Heroku dynos do you need, and which size—An opinionated guide from railsautoscale.com. Adam does a great job explaining and recommending different dyno types, as well as their ideal settings for scaling.

More information at railsautoscale.com/how-many-dynos/.

Heroku Commands

And finally some handy commands for Heroku.

• Server Deploy git push heroku main
• Server Logs heroku logs --tail
• Server Restart heroku restart
• Rails Console heroku run rails console
• Postgres Info heroku pg:info
• Postgres Diagnose heroku pg:diagnose
• Maintenance On heroku maintenance:on
• Maintenance Off heroku maintenance:off
• Database Drop heroku pg:reset DATABASE
• Database Migrate heroku run rake db:migrate
• Database Seed heroku run rake db:seed

Are there other Heroku settings or optimization you like to make? I'd love to hear from you in the comments!