Swarm mode is in the engine and mostly unused

Since 1.12 the engine has had orchestration built in — docker swarm init and a cluster exists. It is genuinely simple and almost nobody is running it, which is worth understanding before choosing it.

docker swarm init
docker stack deploy -c docker-compose.yml shop
docker service scale shop_php=4

The three commands really are the whole thing, against a Kubernetes setup measured in days. The trade is ecosystem: the tooling, the operators, the documentation and the people who have run it in production are all somewhere else. For a small stack on hardware you own it is a defensible choice; for anything expecting to grow a team around it, being unusual is itself a cost.