Fly Apps overview

A Fly App is an abstraction for a group of Fly Machines running your code on Fly.io. You can create and manage your app as a whole using Fly Launch, but you can also have a Fly App with individual Machines running tasks or user code.

For a quick primer on Fly Launch, Fly Machines, and Fly Apps, see Fly.io essentials.

A Fly App can be almost anything

From an admin point of view, a Fly App is just a group of Machines (with optional attached volumes) that belongs to one organization.

From a developer point of view, a Fly App might be:

• a fullstack application (or just part of one)
• a database
• a few Machines running tasks, or a bunch of Machines, all with different configs, doing things you want them to do
• anything you can think of doing with fast-launching Machines, including GPU Machines for AI/ML workloads

All the apps in your organization can communicate over a private network, so it’s also possible to have multiple apps working together as one system.

Components of a Fly App

Fly Apps include:

• app configuration
• provisioned resources
• Anycast IP addresses
• certificates
• custom domains
• secrets
• Fly Volumes (optional)

Fly Apps run on flyd. Learn more about how flyd works and how it came to be in the blog post: Carving the Scheduler Out of Our Orchestrator.

Ways to create an app

There might be an infinite number of potential apps you can run on Fly.io, but there are only a few ways to create one.

Create and deploy with Fly Launch

Fly Launch is perfect for most apps and databases. Use Fly Launch to create your app and then manage the whole lifecycle, from starting to scaling to changing and redeploying. Get started with Fly Launch or learn more about using Fly Launch to create, configure, deploy, and scale your app.

Create an app manually

Most of the time, all you need is Fly Launch to create and manage your app. But you can skip all the handy launch scanners and resource provisioning Fly Launch offers and use the fly apps create command or the Machines API to create an app and then piece it together.

You can get a fly.toml config file from an example app or hand-craft one yourself. Or if you don’t need app-wide config, you can use the Fly App to hold the Machines you plan to spin up individually based on a particular image.

Using the fly apps create command is useful when deploying our autoscaler app, or example apps created by others, that already have fly.toml and Dockerfiles ready to go.

Creating apps with the Machines API might be the right choice if you want to create apps for your own users with pre-defined or custom fly.toml files.

For more information, see the fly apps create docs and the create App resource docs.