Synology Container Manager doesn't work with GitLab Registry

I’m not sure, if this is the correct place for the thread, but Linux seems to be the closest category.

I’m writing here, because the Synolgy support said, that the Container Manager for Synology NAS is developed by docker and I should ask them for a solution:

The situation is the following: I have a GitLab server with a working registry. (I can push and pull images to/from there using a regular docker instance on Ubuntu). I also checked, that the SSL certificate (not self-signed) works properly by calling

openssl s_client -showcerts -servername -connect > cacert.pem

on Ubuntu and on the NAS.

When I try to add the registry as a registration inside Synology Container Manager, it just shows an error (translated, so the original english error might be slightly different):

This operation cannot be performed. The network connection may be unstable or the system may be overloaded. Please try again later.

Adding a regular docker registry from another server works fine, so it seems to be a specific problem between the Container Manager and the GitLab registry. Sadly there doesn’t seem to be a detailed log available …

Does somebody know what the reason could be?

Did you notice “Docker Desktop” before “Linux”? I moved the topic to general discussion.

I don’t have Synology, so I can’t tell, but so far I heard Synology made their own Docker package. And if I remember correctly, “Container Manager” is Synology plugin. I also don’t think Docker Inc develops Synology plugins, so you might have misunderstood something. Maybe they said it must be a Docker issue on a level that they didn’t customize. You could be lucky and find someone in the Docker community who had the same problem, but I have zero experience with Synology and the error message only indicates a network issue so I don’t think I could even guess what the problem is or how it would be related to Docker only and not Synology and its plugin.

Synology is not an officially supported environment by Docker Inc. If they made a plugin, that should be mentioned in the documentation:

Can you quote exactly what Synology support wrote to you?

The translated answer:

Unfortunately, we do not support third-party packages in our support but only offer them on our systems.
At this point, I ask you to contact the developer Docker/Container-Manager directly.

And it seems to be correct. In the package center “Docker Inc.” is listed as the developer of the Container Manager.

It looks like they suggested contacting either the developers of Docker or the developers of Container Manager not saying they are the same. I don’t know who develops the container manager and if it is not a Synology product, why it is on their site as a feature

Can you switch to English on the NAS so we can see the english error message and search for it? Or if you can’t, please, show the original error message without translation.

Also can you run docker commands on Synology instead of using the webbased container manager? Do you get the same message? I assume you got the quoted error on the web UI

It is funny how Synology keeps up this claim since years :smiley:

The Container Manager is a Synology product, which provides a customized Docker Engine under the hood. The sources of the Docker Engine at one point (as in years ago) where forked from the same source code that vanilla Docker bases on today… But, the Container Manager itself and the customizations of their Docker Engine are developed by or on behalf of Synology. This makes Synology clearly the maintainer of the Container Manager and components it provides.

Container Manager interacts with the Docker Engine through the Synology DSM API
Furthermore, for whatever reason the Container Manager (and it’s predecessor) always included a Docker Engine that was already EOL when they made a Container Manager release. Why would it make sense for Docker Inc. to release new vanilla Docker versions for every supported platform (Synology not being one of them), but not for the Synology version if they maintained it?

From my point of view, Synology is clearly the maintainer and support channel of the Container Manager and the dependencies it provides.

Can you do me a favor and ask the Synology support for the public Github repo of the Container Manager? Hint: it is not one of the 131 repos in the docker organization on Github.

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Switched the Synology GUI to English. This is the error:


I’ll try running the docker commands over ssh and will tell you the reults

Running “docker login” and “docker pull” via ssh works without any problem. I can even see the pulled image inside the Container Manager, so it seems to be the same docker instance.

Based on that, it definitely seems to be a bug in the Container Manager code itself and not a problem with the underlying docker.

I’ve just realized something.

In fact, Container Manager was called “Docker” before they renamed it. So the support possibly just referred to the same thing with to alternative names. Doesn’t really change anything just makes more sense and in that case they did not want to indicate that the container manager was developed by the developers of Docker.

On the other hand, why they would think Container Manager is third party, I can’t tell. But you could indeed ask the Synology support where you could find those developers they wanted to recommend. @meyay wrote that the Container Manager uses the DSM api, so even if the container manager is developed by someone / a team that the support don’t know about, I guess the issue could also be in DSM. Or maybe the DSM is not compatible with the container manager? Can you update any of those?

At least you could rule this out.