Docker Compose

You've mastered running single containers. Now you have a photo service and a search service, and you find yourself starting them in the right order, with the right network and volume connections, every time you reboot. Docker Compose turns that manual dance into a single file that declares every service, its network, its persistent volumes, and its dependencies — and starts the whole stack with one command. This is what makes your self-hosted setup reproducible: a friend can clone your repository, run docker compose up -d, and get the exact same system, with the same volumes and networking, on their own machine. It is also the bridge to container orchestration: once your services are declared in a Compose file, moving to Docker Swarm or Kubernetes for multi-host scaling becomes a much smaller step. Concretely, this unlocks: composing a full stack of LLM inference, a vector database for retrieval-augmented generation, and a reverse proxy with TLS — all from one file; declaring health checks and restart policies to make services self-healing; and keeping persistent data safe across container updates.

Think of your self-hosted applications as a household. Each container is a single appliance: a coffee maker, a toaster, a refrigerator. You wouldn't plug each one into a different wall socket with its own separate switch — you'd have a single power strip with a main switch, and you'd arrange the appliances so they share the same counter (the network) and the same pantry (the volume). Docker Compose is that power strip and layout plan. You write down on paper: 'The coffee maker and toaster go on the counter, they share the pantry, and the coffee maker must be turned on before the toaster because toast tastes better with coffee.' That paper is your docker-compose.yml file. When you flip the main switch, everything starts in the right order, connected as described, without you turning on each appliance individually.

Imagine you're moving to a new apartment and you have a list of furniture: a bed, a desk, a bookshelf. You also have a list of things that must be in the same room: the desk and the bookshelf in the study, the bed in the bedroom. You have a list of shared utilities: a power outlet in each room, and a storage closet in the hall. Without a plan, you'd move each item one at a time, and you might end up with the bookshelf in the bedroom because you forgot. Docker Compose is the moving checklist: one piece of paper that says, 'Bed in bedroom, desk and bookshelf in study, then place a power strip in each room and share the closet between all.' You follow the checklist and everything ends up where it should, with the shared utilities in place. Where the analogy breaks: unlike furniture, containers are disposable — you can throw one away and a new one can take its place, but the shared storage (volume) stays, holding your data. Also, the checklist can include dependencies: 'Start the study light before the desk, because you need to see to place the books.' In Compose, you declare which service must start before another, and it waits for the dependency to be healthy.

Docker Compose is a tool that lets you declare all the containers of an application and how they connect — services, networks, volumes, dependencies — in one text file, and then start, stop, and update the whole stack with a single command.

You already know container basics: you can run a single container with docker run, mount a volume for persistent data, and expose a port. Docker Compose builds on that — it's the same operations, but written down in a file so they're reproducible and shareable. It touches two neighbouring topics in your library: Container Orchestration Basics — Compose handles service ordering and basic health checks, which is the beginning of orchestration, and Backup and Hardware Failure — by declaring volumes in Compose, you make it obvious which data must be backed up, and the single-file nature makes restoring a service on a new machine straightforward. It also fits with Portainer Management — you can manage Compose stacks from Portainer's web interface instead of the command line, if you prefer.