Add container support for Docker Swarm environments

[j0nathanr]

Description

Currently, Glance uses the local docker socket to gather container information on the system it's running on. In a docker swarm environment, containers are distributed across multiple hosts (nodes) as docker services. As a result, Glance does not display all labeled docker containers running in the swarm, only the containers currently running on the same node as it is.

The glance agent could be used and deployed globally in the swarm too send container information to the Glance app. This can work the same way services like Portainer and Swarmpit gather container information using their agents. From Portainer's GitHub page:

The Portainer agent is basically a cluster of Docker API proxies. Deployed inside a Swarm cluster on each node, it allows the redirection (proxy) of a Docker API request on any specific node as well as the aggregration of the response of multiple nodes.

I see no potential downsides as swarm mode can be enabled via an environmental variable which defaults to false. Anyone outside a docker swarm environment can simply omit any swarm related configurations.

[mortonpd]

For Docker swarms, would a widget that uses a method closer to traefiks swarm mode not be more appropriate where labels are found on the services rather than on the containers.

This removes the need for agents - but does mean that glance would need to be deployed to a 'manager' node to access the swarm API.

[j0nathanr]

That does seem more appropriate considering the current implementation of docker container support also requires labels. The need to run it on a manager node is fine since the agent route would run on every swarm node anyhow, this just means less overhead.

[kuhree]

Hey 👋 , I also wanted to see this. Just put up a PR with a solution I'm using locally. Would love some feedback if it works for you or not.

Here's a docker image if you're interested: ghcr.io/kuhree/glance:pr-517

Here's how the config looks:

- type: docker-containers
  mode: swarm