[Feature] Multi-client support

[nicholas-fedor]

Is your feature request related to a problem? Please describe.

Watchtower is limited in that it only supports a single Docker client.
In situations where a user has several Docker hosts, either physical or virtual (VM's, LXC's, etc), this results in needing multiple instances of Watchtower for each Docker instance.

Describe the solution you'd like

It would be more efficient to have a single instance of Watchtower that supports managing updates for multiple Docker hosts.

Describe alternatives you've considered

There are currently no alternatives.

Additional context

This has been discussed in the upstream repository:
containrrr/watchtower#1902
containrrr/watchtower#1218

[nicholas-fedor]

I have added this feature request here, as it's something that I would like to eventually tackle.

Watchtower currently focuses on supporting single hosts and implementing this will require touching a significant portion of the codebase.

I would like to first get the other issues squared away before tackling this.

[nicholas-fedor]

There is mention of Dozzle's implementation for multi-client support.
Adding their resources here for reference:

https://dozzle.dev/guide/remote-hosts
https://dozzle.dev/guide/agent

It seems the core of the multi-host support lies here:
https://github.com/amir20/dozzle/blob/master/internal/support/docker/multi_host_service.go

[StefanIva]

I like the idea but am unsure of the implementation. If an agent could be 'pushed' from the Server to the host, it might be an interesting twist of use case? My workflow today is, after provisioning a new host, I install Portainer agent on the host. When Portainer is up, I add additionally 2-3 containers via Stacks. Adding Watchtower or a Watchtower-agent container is the 'same' work.
This is just my way of working. Am sure there are other, that have a better one where this makes sense. Personally, I would much prefer if Watchtower could start working with Podman as memory swapiness is causing issues