Managing Docker Images with Fly.io's Private Registry

Fly.io lets you deploy Docker containers as lightweight Firecracker VMs, running globally. While fly launch supports many frameworks and auto-generates deployment configurations, you can also build and push your own Docker images to Fly.io’s private registry and deploy them manually.

This guide walks through building, pushing, deploying, and managing images via Fly.io’s Docker registry.

Tagging images for the Fly.io registry

Each Fly.io app gets a dedicated registry path in the form of:

registry.fly.io/<your-app-name>

To create a new app:

fly apps create <your-app-name>

App names must be globally unique. You can generate a unique one automatically:

fly apps create --generate-name

Then tag your image for the app’s registry:

docker build -t registry.fly.io/<your-app-name>:<your-tag> .

Authenticating and pushing to the registry

Authenticate Docker to use the Fly.io registry:

fly auth docker

This command updates your ~/.docker/config.json with the required auth token for registry.fly.io. Once authenticated, push your image:

docker push registry.fly.io/<your-app-name>:<your-tag>

Deploying the image

You can deploy images from the Fly.io registry or public registries, depending on where the image is hosted.

To deploy a private image pushed to Fly.io’s registry:

Use the --image option with the fly deploy command:

fly deploy --app <your-app-name> --image registry.fly.io/<your-app-name>:<your-tag>

To deploy a public image from Docker Hub or another public registry:

Specify the image in your fly.toml file:

[build]
  image = "flyio/hellofly:latest"

Reusing images across apps

Although registry URLs are structured per app, access is scoped per organization. This means you can push an image to registry.fly.io/app-1 and use it in another app (e.g. app-2) if both apps are in the same Fly.io organization:

fly deploy --app app-2 --image registry.fly.io/app-1:tag

This pattern is useful for SaaS platforms that build once and deploy many times.

Verifying image existence

You can verify that an image exists in the Fly registry without deploying it using Docker:

docker manifest inspect registry.fly.io/my-app-name:my-tag

This command returns data if the image exists, or exits with code 1 if it does not. It requires prior authentication using fly auth docker.

For most workflows, use the fly deploy --image option with the Fly Docker registry. For advanced flows like multi-app SaaS provisioning, track image tags using docker manifest inspect or associate them with Machines to retain them.

Listing image tags

There is no API or GraphQL query to list all image tags in the registry. Tags only become visible to Fly when they are part of a release. You can view deployed image references with:

fly releases -a my-app-name --image

If you’re using the GraphQL API to query releases, use the following query format:

{
  "query": "query($appName: String!, $limit: Int!) { app(name: $appName) { releases: releasesUnprocessed(first: $limit) { nodes { id version description reason status imageRef stable user { id email name } createdAt } } } }",
  "variables": {
    "appName": "my-app-name",
    "limit": 25
  }
}

This will only return images used in past deploys.

Related use case

Want to optimize your deploys with shared layers and pre-installed dependencies? See the Using base images for faster deployments blueprint.