Docker Registry

You are an expert in deploying applications with Kamal. This skill configures the container registry Kamal pushes your app image to and pulls it from, and logs that registry in and out on your servers with kamal registry.

The default registry is Docker Hub, but you can point Kamal at AWS ECR, GCP Artifact Registry, a local registry, or any other Docker-compatible registry by setting the registry block in config/deploy.yml.

Before you start

Read what the project already has before asking the user questions:

• config/deploy.yml — look for an existing registry: block (server, username, password).
• .kamal/secrets — look for KAMALREGISTRYPASSWORD, the secret Kamal looks up for the registry password.

Knowing which registry the user is on (Docker Hub, ECR, GCP, local, or self-hosted) determines everything below.

How the registry block works

Registry settings live under the registry key in config/deploy.yml:

The password references a secret by name — e.g. KAMALREGISTRYPASSWORD. Kamal looks that name up in your local environment (loaded from .kamal/secrets) instead of storing the literal value in config/deploy.yml, keeping credentials out of source control:

registry:
  username:
    - my-docker-username
  password:
    - KAMAL_REGISTRY_PASSWORD

A local registry (server: localhost:...) is the exception — it needs only server.

Walk-through

1. Choose your registry

2. Store the registry password as a secret

Put the password or token in .kamal/secrets as KAMALREGISTRYPASSWORD so it is read from the environment and kept out of config/deploy.yml. See the secrets skill for pulling this from a vault such as 1Password or AWS Secrets Manager.

3. Add the registry block

Use the snippet for your provider (below), referencing KAMALREGISTRYPASSWORD for the password.

4. Validate

kamal registry login

This logs in to the registry locally and on every server. A clean exit means your server, username, and password are correct.

Registry configurations

Docker Hub (default)

Docker Hub is the default, so you set only username and password:

registry:
  username:
    - your-docker-hub-username
  password:
    - KAMAL_REGISTRY_PASSWORD

Docker Hub creates public repositories by default. To keep your image private, set up a private repository before deploying, or change your Docker Hub default repository privacy to private. See [references/registry-providers.md](references/registry-providers.md).

AWS ECR

Requires the AWS CLI installed locally. An ECR access token is only valid for 12 hours, so use ERB to shell out to the AWS CLI and fetch a fresh token on each run:

registry:
  server: <your aws account id>.dkr.ecr.<your aws region id>.amazonaws.com
  username: AWS
  password: <%= %x(aws ecr get-login-password) %>

GCP Artifact Registry

Use a base64-encoded service account JSON key as the password, with jsonkey_base64 as the username:

registry:
  server: <your registry region>-docker.pkg.dev
  username: _json_key_base64
  password:
    - KAMAL_REGISTRY_PASSWORD

Set KAMALREGISTRYPASSWORD to the base64-encoded key. See [references/registry-providers.md](references/registry-providers.md) for creating the service account, granting roles/artifactregistry.writer, and encoding the key.

Local registry

If server starts with localhost, Kamal starts a local Docker registry on that port and pushes the app image to it:

registry:
  server: localhost:5555

Other registries (custom / self-hosted)

Any other Docker-compatible registry — a self-hosted registry, GitHub Container Registry (ghcr.io), and so on — uses the same three keys: set server to the registry host and provide username / password. See [references/registry-providers.md](references/registry-providers.md).

Logging in and out

kamal registry manages registry authentication locally and on all servers.

$ kamal registry login
$ kamal registry logout

You usually don't run these by hand for a normal deploy — kamal deploy logs in to the Docker registry locally and on all servers as its first step, then builds, pushes, and pulls the image. Use kamal registry login mainly to validate your configuration.

For the full subcommand list (setup, remove, help) and example output, see [references/registry-commands.md](references/registry-commands.md).

Troubleshooting

• docker login fails on deploy — run kamal registry login to surface the error in isolation; check server, username, and that KAMALREGISTRYPASSWORD resolves in .kamal/secrets.
• Image is public on Docker Hub — Docker Hub defaults new repositories to public; create a private repository or change your default privacy setting before deploying.
• ECR auth keeps expiring — the ECR token lasts only 12 hours; the ERB aws ecr get-login-password approach regenerates it on each run.

Related Skills

• build: For building the app image and pushing it to the registry you configure here.
• secrets: For storing KAMALREGISTRYPASSWORD in .kamal/secrets and pulling it from a vault.
• setup: For first-time Kamal setup, where the registry block is first filled in.