Use Docker Secret to set your Portainer Admin User's Password

Requirements

I was deep-diving on creating a decent-sized docker-compose stack with 5+ services in them.
I was also on the look out for some Deployment Pattern where I didn't want to dump all my
Environment Variables into a giant .env file, neither in Production nor in Development.
I decided to create a structure where each service aka. component would have their own dedicated
directory with their respective secrets (credentials) and their configuration files all bundled
together.

I decided upon the following structure:

ComponentName
├── config.component
└── secrets
    └── .env.component

Here the ComponentName could your favourite database, the secrets directory within this directory
would contain a .env.database file with all necessary admin credentials for the initial stack configuration.
The config.component file is a dedicated configuration file (if needed)

I think the structure would work Okay since changes to a component's configuration would be reflected
a bit better in the Git History / Logs

Problem

If you end up having a lot of containers in the stack, docker-compose logs only takes ever so far! You might
decide upon Portainer to make the container management a bit easier through it's UI.

One problem, Portainer doesn't support the Environment Variables Configuration pattern as by many container
based software applications.

It relies on executing command in your docker-compose file to introduce an password into your Portainer's service.

If you have a bit of Software OCD, you are going to hate it! One service not conforming to your dream stack deployment!

Approach

Here comes docker secret to the rescue!

One massive Caveat, according to the documentation, docker secret is only available for Swarm Setting, or it ?!

A blog post from Michael Irwin about using
docker secrets in Development provides a way to trick docker into accepting files as a docker secret and use it into your
service.

Another thing when going through Portainer's Documentation is that, it accepts admin password also through a
password file

We could see some Puzzle Pieces falling into place here!

Solution

Let's start with our structure mentioned above:

portainer
└── secrets
    └── portainer-admin-password
|- docker-compose.yml

Instead of an .env we rename the file to portainer-admin-password where you can set your password.

Your docker-compose.yml will then look as follows:

version: '3.7'
services:
  portainer:
      image: portainer/portainer-ce:latest
      container_name: sys_portainer
      restart: always
      volumes:
        - /var/run/docker.sock:/var/run/docker.sock
      command:
        - '--admin-password-file=/run/secrets/portainer_admin_password'
        - '--no-analytics'
      networks:
        - some_network
      ports:
        - "9000:9000"
      secrets:
        - portainer_admin_password

networks:
  some_network:
    external: true

secrets:
  portainer_admin_password:
    file: ./portainer/secrets/portainer_admin_password

Breaking it down functionally!

secrets:
  portainer_admin_password:
    file: ./portainer/secrets/portainer_admin_password

mounts the file as a docker secret into the compose file. Since it is a file mount, it will be
available in the following directory /run/secrets/<KEY_NAME_IN_SECRETS_section> since our key
is the same name as that of the file (in order to avoid any discrepancy), the content of the file
will be consumed by the --admin-password-file flag during the stack initialization.

Voilá! You now have a similar structure without having to hardcode passwords or sensitive information
into your docker-compose.yml file