It supports docker swarm, but I've never used it like that.
As I may need multi node in the future, I was asking the question to see if it would make it 'easy' to orchestrate multiple containers.
The simplicity of Dokku is hard to beat, however.
edit: Well, it would appear that the very maintainer of Dokku himself replied to the parent comment. My information is clearly outdated and I'd only look at this comment[0] to get the proper info.
Dokku is multi node. It supports docker-local (single node) and k3s (multi-node) as schedulers, with most features implemented as expected when deploying to k3s.
