I’ve done this a lot when using distillery - for example, bundling a script which will execute an ecto.migration task.

Here’s an example of with this kind of configuration.

The reason this is important is for kubernetes. Kubernetes has various lifecycle hooks such as healthcheck, startup, etc.

It’s very nice to provide the cluster administrators with the means to run extra tasks - and it’s even nicer when you package this with the application so that you have targets like this :

docker run --rm -ti \
                -e POSTGRES_HOSTNAME=postgres.notifications \
                -e POSTGRES_PASSWORD=postgres \
                -e POSTGRES_DATABASE=notifications_dev \
                -e DATADOG_AGENT_HOSTNAME=localhost \
                -e DATADOG_AGENT_APM_PORT=8126 \
                -e EXQ_HOST=redis.notifications \
                -e EXQ_PASSWORD= \
                -e EXQ_PORT=6379 \
                -e EXQ_NAMESPACE=exq \
                --name notificatons \
                --network notifications \
                --hostname notifications  \
                -p 4000:4000 \
                foo/notifications:latest help
Usage: notifications COMMAND [ARGS]

The known commands are:

    start                  Starts the system
    start_iex              Starts the system with IEx attached
    daemon                 Starts the system as a daemon
    daemon_iex             Starts the system as a daemon with IEx attached
    eval "EXPR"            Executes the given expression on a new, non-booted system
    rpc "EXPR"             Executes the given expression remotely on the running system
    remote                 Connects to the running system via a remote shell
    restart                Restarts the running system via a remote command
    stop                   Stops the running system via a remote command
    pid                    Prints the OS PID of the running system via a remote command
    version                Prints the release name and version to be booted
--> run_migration          Run ecto migration
--> update_email_templates Update email templates (for example)

ERROR: Unknown command help