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Convert from Docker Compose

Docker Compose has been a popular tool for developers to define and run multi-container applications on their desktops and local machines. When it comes to production workloads, organizations have selected Kubernetes which creates a gap from the development environment to production. Acorn on the other hand, provides a way to define and run multi-container applications suitable for development and production with the same artifact and tooling.

This provides a high level guide to manually translate Docker Compose concepts into Acornfiles. There isn't an automated tool available at this time, but this guide should cover some of the basics.

Conceptual Differences​

AML vs. YAML​

An Acornfile is written in Acorn Markup Language (AML) where Docker Compose files are written in YAML. The syntax is similar, but there are some differences.

Compose Services​

In Docker Compose, a service is a where containers are defined. In Acorn, containers are defined under containers.

Compose Networks​

There is no direct translation for Docker Compose networks in Acorn. Acorn has its own networking model that involves a single network for the containers in a project / region.

Compose Configs​

Compose provides a top level configs key that can be used to define configuration values to be consumed in compose 'services'. Acorn has the ability to provide configuration data to containers through files, secrets, and arguments to the Acorn.

Acorn Services​

Acorn has the concept of services that provide a way to define an interface for containers to consume the components. These service interfaces can be implemented by a container or a cloud provider. If they both implement the same interface, they can be swapped out without any changes to the consuming Acornfile.

Bind mounts​

Acorn doesn't support directly mounting the filesystem into a container. Instead it copies files from the local filesystem to the container filesystem. This allows you to work with Acorns in cloud environments.

Example​

Two container Docker Compose file​

To show basic usecase, lets Walking through a translation of a Docker Compose file to an Acornfile. We will convert this Docker Compose file to an Acorn that has a container for the Gitea application and consumes a Postgres service from another Acorn.

Here is our Gitea Docker Compose file:

services:
  gitea:
    image: gitea/gitea:latest
    environment:
      - DB_TYPE=postgres
      - DB_HOST=db:5432
      - DB_NAME=gitea
      - DB_USER=gitea
      - DB_PASSWD=gitea
    restart: always
    volumes:
      - git_data:/data
    ports:
      - 3000:3000
  db:
    image: postgres:alpine
    environment:
      - POSTGRES_USER=gitea
      - POSTGRES_PASSWORD=gitea
      - POSTGRES_DB=gitea
    restart: always
    volumes:
      - db_data:/var/lib/postgresql/data
    expose:
      - 5432
volumes:
  db_data:
  git_data:

The above file describes two services (containers) that will run Gitea and Postgres as containers. To persist the data, it creates two volumes for the containers to store the data.

Now lets look at the corresponding Acornfile:

services: postgres: {
    image: "ghcr.io/acorn-io/postgres:v#.#.#-#" // pulls the latest 
    serviceArgs: dbName: "gitea"
}

containers: gitea: {
    image: "gitea/gitea:latest"
    ports: publish: "3000/http"
    dirs: "/data": "volume://git-data"
    env: {
        DB_TYPE: "postgres"
        DB_HOST: "@{services.postgres.address}"
        DB_NAME: "@{services.postgres.data.dbName}"
        DB_USER: "@{services.postgres.secrets.admin.username}"
        DB_PASSWD: "@{services.postgres.secrets.admin.password}"
    }
}

volumes: "git-data": {}

Here the gitea container is using the postgres service for the database. The postgres service is another Acorn that deploys Postgres and provides the information needed to the the gitea container to connect to the database. The benefit of this deployment is that we could also use the RDS Acorn in AWS to deploy a Postgres RDS instance and the gitea container would not need to have any of its settings changed.

The gitea container is publishing port 3000 which will have a URL and corresponding TLS Certificate provided by Acorn. The volume for the gitea container is backed by a persistent volume in the cluster and will be available to the container across restarts.