Working with image registries

When Maestro needs to start a new container, it will do whatever it can to make sure the image this container needs is available; the image full name is specified at the service level.

Maestro will first check if the target Docker daemon reports the image to be available. If the image is not available, or if the -r flag was passed on the command-line (to force refresh the images), Maestro will attempt to pull the image.

To do so, it will first analyze the name of the image and try to identify a registry name (for example, in my-private-registry/my-image:tag, the address of the registry is my-private-registry) and look for a corresponding entry in the registries section of the environment description file to look for authentication credentials. Note that Maestro will also look at each registry’s address FQDN for a match as a fallback.

You can also put your credentials into ${HOME}/.dockercfg in the appropriate format expected by Docker and docker-py. Maestro, via the docker-py library, will also be looking at the contents of this file for credentials to registries you are already logged in against.

If credentials are found, Maestro will login to the registry before attempting to pull the image.

Additionally, you can configure a retry policy or image pull errors or a per-registry basis. You can specify a maximum number of retries, and a list of returned HTTP status codes to retry on. For example, the following configuration will make two attempts to pull images from the registry if a 500 is returned.

    username: user
    password: super-secret
      attempts: 2
        - 500