This is a technology preview.

Looking for feedback on everything: technical correctness, developer experience, what feature should be focused on next...

See also the RFC: Terraforming Rails on fly.io and Getting started with Terraform and Machines .


Go ahead and download Terraform if you haven't yet.

Optionally, either configure wireguard or run a proxy. If you do neither, a proxy will be dynamically started and stopped as needed.

Create a Rails Project

rails new welcome; cd welcome

Now use your favorite editor to make a one line change to config/routes.rb:

 Rails.application.routes.draw do
   # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html

   # Defines the root path route ("/")
-  # root "articles#index"
+  root "rails/welcome#index"

Install fly.io-rails gem:

 bundle add fly.io-rails

Source to this gem is on GitHub. If adopted, it will move to the superfly organization.

Generate Terraform Configuration

bin/rails generate fly:terraform

The terraform generator supports a number of options, for now it is worth letting them all default. For completeness, the current list of options supported is:

  • --name - application name. If not specified, a name will be generated for you.
  • --org - the fly organization. Defaults to personal.
  • --region - one or more regions to deploy this app. If not specified, fly wil pick one for you based on your location.

More options can and should be added. See Fly terraform provider documentation for ideas.

Deploy the Application

bin/rails deploy

What this will do is:

  • Build your docker image using a remote builder
  • Push your image to the fly repository
  • Update main.tf with the name of the new image
  • Create a machine to run your release task
  • Wait for the release to complete
  • Remove the release machine
  • Run terraform apply -auto-approve

Once this completes -- whether it works or not, and there are plenty of things that can go wrong -- feel free to modify main.tf and rerun terraform commands directly. You can even terraform destroy and rm terraform.tfstate and start over. What's important is main.tf already reflects the name of the latest image.

Also, because a minimal fly.toml file was generated, you can use commands like fly open, fly ssh console and fly logs.

Open Issues

  • It would be ideal to see the release task output in real time. Next best would be to show the output when the task completes. Currently the output isn't show and the machine is removed if the release was successful. If the release fails, the machine is not removed and the command to show the logs is provided to the developer.
  • At the moment, the first image in the main.tf is updated when a new build is complete, and the first machine listed is run to perform a release. Perhaps the template used to generate this should set the SERVER_COMMAND environment variable explicitly and the deploy command should scan for this in order to determine which image is to be updated and which machine is to be executed.
  • If you deploy using fly deploy directly (perhaps with GitHub actions?), the image name in main.tf won't be updated. You can obtain the current image name via the following command:

     fly ssh console -C 'printenv FLY_IMAGE_REF'