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Deploying a Ruby application on Fly.io requires two essential ingredients: a Gemfile and a config.ru file. Full-stack frameworks like Rails, Padrino, and Hanami provide both of these for you. Micro-frameworks like Sinatra, Camping, and Rack itself require you to create your own.

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Gemfile

If you don’t have a gemfile, the best way to get started is to run:
Once this file is created, proceed to add gems needed by your application, for example:
The Gemfile needs to include the framework you may be using, so if you are using, for example, Sinatra or Camping, add that gem too. Finally add a web server, like puma, thin, or falcon. If you are not sure what web server to use, puma is a safe bet:

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config.ru

The most basic config.ru file would be the following:
Phusion Passenger guides provide a helpful list of starter config.ru files for various Ruby web frameworks. We’re now ready to run the app locally.

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Running The Application

Run bundle exec rackup to start the application
If you see a message suggesting that you need to run bundle binstub rack, that message can be safely ignored. And connect to localhost:9292 to confirm that you have a working Ruby application. Now to package it up for Fly.

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Install Flyctl and Login

We are ready to start working with Fly and that means we need flyctl, our CLI app for managing apps on Fly. If you’ve already installed it, carry on. If not, hop over to our installation guide. Once that’s installed you’ll want to log in to Fly.

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Launch the app on Fly

To launch an app on fly, run flyctl launch in the directory with your source code. This will create and configure a fly app for you by inspecting your source code, then prompt you to deploy.
First, this command scans your source code to determine if it meets the requirements for a deployable Ruby app. After your source code is scanned and the results are printed, you’ll be prompted for an organization. Organizations are a way of sharing application and resources between Fly users. Every fly account has a personal organization, called personal, which is only visible to your account. Let’s select that for this guide. Next, you’ll be prompted to select a region to deploy in. The closest region to you is selected by default. You can use this or change to another region. Finally you will be given the option to start a Postgres and/or a Redis database. If you need one or both, it is convenient to set them up now. Otherwise you can always add them later. At this point, flyctl creates an app for you and writes your configuration to a fly.toml file. You’ll then be prompted to build and deploy your app. Once complete, your app will be running on fly.

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Config First!

Most Dockerfiles expect some configuration settings through ENV. The generated fly.toml file has a place for you to add your custom ENV settings. It’s the [env] block.
Add whatever values your Dockerfile or container requires. Sometimes you have secrets that shouldn’t be checked in to git or shared publicly. For those settings, you can set them using fly secrets.
You can list the secrets you’ve already set using fly secrets list
The values aren’t displayed since they are secret!

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Deploying to Fly

To deploy changes to your app, just run:
This will lookup our fly.toml file, and get the app name from there. Then fly will start the process of deploying our application to the Fly platform. Flyctl will return you to the command line when it’s done.

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Connecting to the App

The quickest way to browse your newly deployed application is with the flyctl apps open command.
Your browser will be sent to the displayed URL.

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Arrived at Destination

You have successfully built, deployed, and connected to your first Ruby application on Fly. You can monitor and explore your app with the following command: