[BUG] Docker Swarm mode not seeing images/containers

[mihakrumpestar]

Describe the bug
Running this on a docker swarm mode results in Cup not seeing any images/containers.

To Reproduce

Run on Docker swarm mode with containers deployed as stacks (only sees itself when running CLI, does not see even itself when deployed as Docker Swarm stack):

docker run -tv /var/run/docker.sock:/var/run/docker.sock ghcr.io/sergi0g/cup check

Expected behavior
Works on regular docker install, list images and updates.

Screenshots
If applicable, add screenshots to help explain your problem.

System info (please complete the following information):

[admin@docker-swarm-0 ~]$ fastfetch
                  -`                     admin@docker-swarm-0
                 .o+`                    --------------------
                `ooo/                    OS: Arch Linux x86_64
               `+oooo:                Host: SY-YL B550M
              `+oooooo:             Kernel: Linux 6.8.12-1-pve

[admin@docker-swarm-0 ~]$ docker version
Client:
 Version:           28.0.0
 API version:       1.48
 Go version:        go1.24.0
 Git commit:        f9ced58158
 Built:             Mon Feb 24 21:55:48 2025
 OS/Arch:           linux/amd64
 Context:           default

Server:
 Engine:
  Version:          28.0.0
  API version:      1.48 (minimum version 1.24)
  Go version:       go1.24.0
  Git commit:       af898abe44
  Built:            Mon Feb 24 21:55:48 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v2.0.3
  GitCommit:        06b99ca80cdbfbc6cc8bd567021738c9af2b36ce.m
 runc:
  Version:          1.2.5
  GitCommit:        
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Additional context
Add any other info that you think may be useful here.

[sergi0g]

Hello! Thanks for opening this issue!

I haven't tested with swarm at all, but it should be working fine. I'll try to investigate as soon as I can and I'll update you.

[sergi0g]

I tried running a local swarm with my server as manager and my PC as a worker and started a stack with 2 replicas running Cup. All images were checked normally. Honestly, I have no idea what could be going wrong. Could you please share your configuration so I can test that too?

[mihakrumpestar]

I started from stretch. I pulled the image, and try to run it:

I have no idea what is going on.

[mihakrumpestar]

After looking in the code it seems that it hit my private Registry (which I changed after), which uses "Basic auth", but Cup seems to not support that. I did now exclude it, and it is running now.

While I have much more images:

[mihakrumpestar]

I have also noticed that images used by swarm stack deploys are not actually by default usable by normal docker.

If you prune all whole setup and then deploy a stack, and then try to do: docker image history <some image that got deployed in stack> it will respond that the image is not available locally.

Example where the image is in docker images used only in Docker Stack from image above but not visible to regular Docker:

If you then pull it (it will then use/transfer the stack image) and run the history command again it will work.

It seems that swarm stacks handle images a bit differently than regular docker compose and docker commands.

[sergi0g]

Hello! Thanks for debugging the issue! The extra images are most likely not shown because they don't have a tag. Are you pulling by digest? I'll try to reproduce the problem you described and further debug it.

[mihakrumpestar]

For Dozzle I used:

services:
  dozzle:
    image: mirror.gcr.io/amir20/dozzle:latest
    ...

All my stacks except for some exceptions all have latest.

I am not sure why they don't have a tag when inspecting them with docker images command.

[mihakrumpestar]

Hello! Thanks for debugging the issue! The extra images are most likely not shown because they don't have a tag. Are you pulling by digest? I'll try to reproduce the problem you described and further debug it.

It appears you are right, Docker Swarm uses image with digest (label gets resolved to digest), so if Cup checks using label, it won't work.

Docs: https://docs.docker.com/engine/swarm/services/#specify-the-image-version-a-service-should-use

[mihakrumpestar]

That also explains why docker image history ... only saw them after docker pull ... assigned a label to the image (as it didn't have it due to being pulled by docker swarm). And the Cup dashboard only shows images that I tested using docker pull.

[sergi0g]

I need both the tag and the digest to check for an update, so I think Swarm is unsupported. I'm really sorry! I'll try to find another way to check for updates without the tag, but I doubt I'll find anything.

[mihakrumpestar]

No worries, I am using Shepherd and it works.

I just really liked the Cup's UI and on-demand updates, so I wanted to test it out. Docker Swarm just has many edge cases, which effect a lot of the tooling unfortunately.

[sergi0g]

Hey @mihakrumpestar!

I took a look into how Shepherd works and I'm going to try to add the required functionality to Cup. It should be able to check for updates to Docker Swarm images (although it won't be handling automatic updates like Shepherd, as I think that's beyond the scope of this project).

Can you please test? Grab a binary from here or use the ghcr.io/sergi0g/cup:v3.2.0-alpha.1) Docker image.

I hope it works for you!

[mihakrumpestar]

Hi, I run it again using the image, and it seems to work:

Thank you 🙂

[mihakrumpestar]

Probably unrelated, all ghcr.io images are not being able to be checked:

Nevermind, I just redeployed it, and it checked them fine now.

[sergi0g]

@mihakrumpestar I'm glad it worked for you. I'm waiting to see if #64 was caused by this. If it wasn't I'll release a new stable version and close this issue.