Multiple Fly Applications

This guide discusses how to manage multiple Fly applications within a Rails projects. This is useful for Rails projects that need to run other services, like running a pool of Puppeteer servers that your Rails app calls to take screenshots of web pages.

What is a Fly application?

Your Rails application is a Fly application, which means it has the following few things:

  • A fly.toml file in the root directory
  • A Dockerfile in the root directory that describes the image
  • A “server” running on Fly’s infrastructure.

So how do you spin up multiple Fly applications for a single Rails project?

Creating a Fly application within a Fly application

The important thing about creating multiple Fly applications within a project is keeping them organized. For our example, we’ll setup a Redis server application and keep it in the ./fly/applications folder within our project repo.

Let’s get started by running the following commands:

mkdir -p fly/applications/redis
cd fly/applications/redis

From inside the fly/applications/redis folder, run:

fly launch --image flyio/redis:6.2.6 --no-deploy --name my-project-name-redis

This command will create a Dockerfile and fly.toml file that can be further configured for your application’s needs.

Next, deploy the application:

fly deploy

Accessing from the root application

Fly creates DNS hosts for each of your applications that are not surprising.

Deploying updates

In the future, when it’s time to deploy updates to your Fly application within a Fly application, run:

cd fly/application/redis
fly deploy

That’s it.