After creating a Container Service with Swarm orchestration, setting up an SSH tunnel to the manager, and setting the DOCKER_HOST environment variable, I was able to issue commands to the Swarm manager on Azure.
Then I tried to deploy a Docker stack using a compose file (with the native docker stack up command, not the docker-compose utility), and I got an error message like
Daemon uses API version 1.24, stack deploy requires version 1.25.
(I don't have the exact text right now, but I think I remember the versions correctly.)
Similarly, issuing docker inspect swarm outputs
No such object: swarm
(Again, not exact quote.)
If I'm not mistaken, these errors are because the Docker version is too old, and does not have native Swarm Mode yet. And I only realized this after reading the Note about it in this article.
I know there are a couple of ways described in said article to make it work, one being acs-engine, but they are all far from straightforward. At least relative to how easy it was to access the Manager using just SSH and the local docker command.
So my question is really: Are there any plans to upgrade to a newer Docker version, and to have complete support for native Swarm Mode as orchestration? Or am I expected to just use Kubernetes (or something like that) instead?
In any case, I think it would be worth considering to somehow communicate better the fact that the supported Swarm is the legacy one, and not the native Swarm Mode.
Docker CE is available in preview in a number of regions and is rolling out across all regions now. See https://github.com/Azure/ACS/blob/master/announcements/2017-08-04_additional_regions.md
Docker Inc. also provide Docker for Azure as @janshair says in another answer.