SQLite3

While Rails applications on fly.io normally run on Postgres databases, you can choose to run them on sqlite3.

To make this work, you will need to place your databases on persistent Volumes as your deployment image will get overwritten the next time you deploy.

Volumes are limited to one host, this currently means that fly.io hosted Rails applications that use sqlite3 for their database can't be deployed to multiple regions. But watch this space, as things could be changing soon.

Following are the steps required to make this work:

Create Volume

fly volumes create name

Replace name with your desired volume name. Only alphanumeric characters and underscores are allowed in names.

Optionally, you may specify the size of the volume, in gigabytes, by adding a --size int argument. The default volume size is 3 gigabytes.

Now set the following secret, again replacing the name with what you selected:

fly secrets set DATABASE_URL=sqlite3:///mnt/name/production.sqlite

Mount and Prep for Deployment

Add the following to your fly.toml, once again replacing the name with what you selected, this time in two places:

[mounts]
  source="name"
  destination="/mnt/name"

Next move the depency on the db:migrate task from the release to server in lib/tasks/fly.toml:

 # commands used to deploy a Rails application
 namespace :fly do
   # BUILD step:
   #  - changes to the filesystem made here DO get deployed
   #  - NO access to secrets, volumes, databases
   #  - Failures here prevent deployment
   task :build => 'assets:precompile'

   # RELEASE step:
   #  - changes to the filesystem made here are DISCARDED
   #  - full access to secrets, databases
   #  - failures here prevent deployment
-  task :release => 'db:migrate'
+  task :release

   # SERVER step:
   #  - changes to the filesystem made here are deployed
   #  - full access to secrets, databases
   #  - failures here result in VM being stated, shutdown, and rolled back
   #    to last successful deploy (if any).
-  task :server do
+  task :server => 'db:migrate' do
     sh 'bin/rails server'
   end
 end

You can also silence warnings about running sqlite3 in production by adding the following line to config/environments/production.rb:

 Rails.application.configure do
+  config.active_record.sqlite3_production_warning=false

Deploy

These changes can be deployed using fly deploy.