Run a Ruby App

Getting an application running on is essentially working out how to package it as a deployable image. Once packaged it can be deployed to the global application platform.

In this guide we'll learn how to deploy a Ruby application on

The Helloruby Application

Our example will be a basic "hello world" example using Sinatra. We'll assume that you already have Ruby and Bundler installed.

You can get the code for the example from the helloruby GitHub repository. Just git clone to get a local copy. Here's all the code for our app.rb:

#!/usr/bin/env ruby

require 'rubygems'
require 'bundler/setup'
require 'sinatra'

get '/' do
  "<h1>Hello From Ruby on Fly!</h1>"

get '/:name' do
  "<h1>Hello From Ruby on Fly!</h1></br>and hello to #{params[:name]}"

We'll call this file app.rb. We also need to install Sinatra - bundle add sinatra and create a file for Rack to start up the server:


require './app.rb'

run Sinatra::Application

We're now ready to run the app locally.

Running the Application

Run rackup to start the application

[2020-08-18 14:46:21] INFO  WEBrick 1.4.2
[2020-08-18 14:46:21] INFO  ruby 2.6.5 (2019-10-01) [x86_64-darwin19]
[2020-08-18 14:46:21] INFO  WEBrick::HTTPServer#start: pid=39638 port=9292

And connect to localhost:9292 to confirm that you have a working Ruby application. Now to package it up for Fly.

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 thats installed you'll want to log in to Fly.

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.

flyctl launch
Scanning source code
Detected Ruby app
Using the following build configuration
        Builder: paketobuildpacks/builder:base
? Select organization: Demo (demo)
? Select region: ord (Chicago, Illinois (US))
? Would you like to deploy now? Yes

Deploying helloruby

First, this command scans your source code to determine how to build a deployment image as well as identify any other configuration your app needs, such as secrets and exposed ports.

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.

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.

Inside fly.toml

The fly.toml file now contains a default configuration for deploying your app. In the process of creating that file, flyctl has also created a Fly-side application slot of the same name, "helloruby". If we look at the fly.toml file we can see the name in there:

app = "helloruby"

  builder = "paketobuildpacks/builder:base"
  buildpacks = [""]

  internal_port = 8080
  protocol = "tcp"

    hard_limit = 25
    soft_limit = 20

    handlers = ["http"]
    port = "80"

    handlers = ["tls", "http"]
    port = "443"

    interval = 10000
    timeout = 2000

The flyctl command will always refer to this file in the current directory if it exists, specifically for the app name/value at the start. That name will be used to identify the application to the Fly platform. The rest of the file contains settings to be applied to the application when it deploys.

We'll have more details about these properties as we progress, but for now, it's enough to say that they mostly configure which ports the application will be visible on.

Deploying to Fly

To deploy changes to your app, just run just run:

flyctl deploy

This will lookup our fly.toml file, and get the app name helloruby from there. Then flyctl will start the process of deploying our application to the Fly platform. Flyctl will return you to the command line when it's done.

Viewing the Deployed App

Now the application has been deployed, let's find out more about its deployment. The command flyctl info will give you all the essential details.

flyctl status
  Name     = helloruby
  Owner    = demo
  Version  = 1
  Status   = running
  Hostname =

d61b5d88 1       fra    run     running 1 total, 1 passing 0        2m21s ago

Connecting to the App

The quickest way to browse your newly deployed application is with the flyctl open command.

flyctl open

Your browser will be sent to the displayed URL. Fly will auto-upgrade this URL to a HTTPS secured URL.

Bonus Points

  • If you want to know what IP addresses the app is using, try flyctl ips list:
flyctl ips list
TYPE ADDRESS                             CREATED AT
v4                       31m16s ago
v6   2a09:8280:1:ec33:28d:5d1c:e0e9:2839 31m16s ago

Arrived at Destination

You have successfully built, deployed, and connected to your first Ruby application on Fly.