Using the Fly Docker registry#

Fly.io lets you deploy Docker containers that will be compiled as a Firecracker VM and run in locations around the world.

Fly offer a number of ways to build and deploy apps. For many frameworks you can run fly launch and it will detect the framework and configure a container for you. For others you can pass it a Dockerfile which will be built and deployed. But you can also push your own images to a Docker registry and deploy them to Fly.

Today I figured out how to use Fly’s own registry to deploy an app.

Tagging images for the Fly registry#

Fly’s registry is called registry.fly.io. To use it, you need to tag your Docker images with a tag that begins with that string.

Every Fly app gets its own registry subdomain. You can create apps in a number of ways, but the easiest is to use the Fly CLI:

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flyctl apps create datasette-demo

Fly app names must be globally unique across all of Fly - you will get an error if the app name is already taken.

You can create an app with a random, freely available name using the --generate-name option:

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~ % flyctl apps create --generate-name
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? Select Organization: Simon Willison (personal)
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New app created: rough-dew-1296

Now that you have an app name, you can tag your Docker image using:

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registry.fly.io/your-app-name:unique-tag-for-your-image

If you are building an image using Docker on your machine, you can run this command in the same directory as your Dockerfile:

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docker build -t registry.fly.io/datasette-demo:datasette-demo-v0 .

Pushing images to the registry#

In order to push your image to Fly, you will first need to authenticate.

The flyctl auth docker command will do this for you:

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~ % flyctl auth docker
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Authentication successful. You can now tag and push images to registry.fly.io/{your-app}

This works by hooking into Docker’s own authentication mechanism. You can see what it has done by looking at your ~/.docker/config.json file. Mine looks like this:

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{
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  "auths": {
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    "registry.fly.io": {
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      "auth": "... secret token here ..."
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    }
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  ,
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  "experimental": "disabled",
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  "stackOrchestrator": "swarm"
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}

Now you can push your image to the registry like this:

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docker push registry.fly.io/datasette-demo:datasette-demo-v0

Deploying an image#

Now that your image is pushed, you can deploy an instance of it like this:

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flyctl deploy --app datasette-demo \
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  --image registry.fly.io/datasette-demo:datasette-demo-v0

A few seconds later your app will be running at:

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https://name-of-your-app.fly.dev/