docker-swarm vs.docker-compose on single host in production

Question

Is there a reason to use docker-swarm instead of docker-compose for deploying a single host in production?

I'm currently rewriting an existing application. My predecessors set up the application using docker-swarm. But I do not understand why: the application will only consist of a single host running a couple of services. These services will only supply some local information on the customer network via a REST-Api to a kubernetes cluster (so no real load or reason to add additional hosts).

I looked through the Docker website and could not find a reason to use docker-swarm to deploy a single host, apart from testing a deployment on a single host dev environment.

Are there benefits of using docker-swarm compared to docker-compose regarding deployment, networking, etc...?

Answer 1

Docker Swarm and Docker Compose are fundamentally different animals. Compose is a build tool that lets you define and configure a group of related containers, whereas swarm is an orchestration tool that manages multiple docker engines in a way that lets you treat them (somewhat) as a single unit. Swarm exposes an API that is mostly compatible with the Docker Remote API, which allows existing applications to use Swarm to scale horizontally without having to completely overhaul the existing interface to the container engine.

That said, much of the functionality in Docker Compose that overlaps with Docker Swarm has been added incrementally. Compose has grown over time, and the distinction between the two has narrowed a bit. Swarm was eventually integrated into the Docker engine, and Docker Stack was introduced, allowing compose.yml files to be read directly by Docker, without using Compose.

So the real question might be: what is the difference between docker compose and docker stack? Not a whole lot. Compose is actually a separate project, written in Python that uses the Docker API under the hood. Stack does much of the same things as Compose, but is integrated into Docker. Stack also wants pre-built images, while compose will handle those image builds for you, which makes compose very handy for development.

What you are dealing with might be a product of a time when these 2 tools were a lot more distinct. Docker Swarm is part of Docker, and it allows for easy scaling if needed (even if you don't need it now, it might be good down the road). On the other hand, Compose (in my opinion anyway) is much more useful for development situations where you are making frequent tweaks to your images, and rebuilding.