Dappnode packages are built upon Docker containers. The heart of defining how these containers run and interact lies in the docker-compose.yml file. In this guide, we will explain the typical structure of the docker-compose.yml file for a Dappnode package.

A simple docker-compose.yml file looks like this:

version: "3.5"
services:
  test.public.dappnode.eth:
    build: .
    image: "test.public.dappnode.eth:0.1.0"
    restart: unless-stopped

This example illustrates the basic elements, which include the version of the docker-compose file, services, and the service's basic attributes.

A more intricate docker-compose.yml file could look like this:

version: "3.5"
services:
  beacon-chain:
    build:
      context: beacon-chain
      args:
        UPSTREAM_VERSION: v4.0.7
    volumes:
      - "beacon-chain-data:/data"
    ports:
      - "12603:12603/tcp"
      - "12603:12603/udp"
    restart: unless-stopped
    environment:
      P2P_PORT: 12603
      CHECKPOINT_SYNC_URL: "https://checkpoints.mainnet.lukso.network"
      EXTRA_OPTS: ""
      LOG_VERBOSITY: info
      MIN_SYNC_PEERS: "0"
      MAX_PEERS: "250"
      SUBSCRIBE_ALL_SUBNETS: "true"
  validator:
    build:
      context: validator
      args:
        UPSTREAM_VERSION: v4.0.7
    volumes:
      - "validator-data:/data"
    restart: unless-stopped
    environment:
      LOG_VERBOSITY: info
      GRAFFITI: validating_from_DAppNode
      ENABLE_DOPPELGANGER: "true"
      EXTRA_OPTS: ""
volumes:
  beacon-chain-data: {}
  validator-data: {}

In the complex example, you'll find:

• Multiple services (like beacon-chain and validator).
• Build arguments, such as the relevant UPSTREAM_VERSION.
• Defined volumes, ports, and environment variables.

• All environment variables (envs) defined in the docker-compose.yml file will be visible in the package config post-installation. Users can modify these.
• If the package has a setup-wizard, those environment variables not set within it will be hidden by default in the configuration. Users can view these by selecting "Show advanced config".

• The UPSTREAM_VERSION argument is mandatory if you wish to leverage GitHub actions that automatically create PRs when there's a new release in the upstream repository.

• In the Dockerfile, UPSTREAM_VERSION is usually declared and used like this:

  ARG UPSTREAM_VERSION
  FROM consensys/teku:$UPSTREAM_VERSION

:::note The upstreamVersion and upstreamRepo fields need to be defined in the dappnode_package.json file for the GitHub actions to work. Here is an example:

{
  ...
  "upstreamVersion": "23.8.0",
  "upstreamRepo": "ConsenSys/teku",
  ...
}

:::

• EXTRA_OPTS is an environment variable that allows users to add any flags that might not have been included by default.

• Here's a typical use case for EXTRA_OPTS in the entrypoint script:

  exec /opt/teku/bin/teku \
      --network=prater \
      ...(omitting other flags) \
      --log-destination=CONSOLE \
      $EXTRA_OPTS