Listen on UDS inside a container

[sebadob]

I have an issue with UDS inside a container and was wondering, if I was missing something or need to do anything special about it when using actix-web.

I do have an application that works just like expected when I .bind_uds("example.sock")?.run().await, but when I try to do the same inside a container, it gets stuck completely at that point and the only way to stop it is a kill -9. I am using the exact same config / setup and even the same socket file. Permissions on the file are ok and match the user inside the container, and even after chmod 0777 it does not work, so it cannot be about file permissions or a mismatch with the user inside the container.

I am mounting the socket with a normal volume mount like -v /tmp/example.sock:/example.sock. When I don't mount the socket file, the app starts fine and works like expected (with the only problem though that the socket file only exists inside the container of course), but as soon as I add the volume mount for the socket without changing anything else, actix-web gets stuck and everything freezes as soon as it gets to .bind_uds("example.sock")?.run().await.

Am I missing something or is there anything I need to do about it?

[robjtede]

Just to check, what's your host OS? I only have macOS access and can believe that there's some oddities if running a Docker image on top of macOS and sharing a UDS file, so I'll write up a simple test case for debugging if that's your setup.

[sebadob]

I was testing on Fedora 42. However, I was able to somewhat "solve" this. I am now pretty sure that it's something about the container engine, and actix-web is most probably just fine.

I did some more tests, and when I place the socket file inside a directory, and I then mount the whole directory inside the container instead of mounting the file only, it works just fine.

The only thing that maybe could be improved is this kind of deadlock state the framework gets into during startup, but I am not sure what exactly this is about and if there is even a way to catch this.

Just for completeness, what I did before, just like it's mentioned in a lot of documentation online for mounting sockets:

docker run -it --rm \
    -v /tmp/example.sock:/tmp/example.sock \
    my_image

This makes actix-web lock completely during binding to the socket file, but I don't know why.

When I instead

mkdir /tmp/my_sock

docker run -it --rm \
    -v /tmp/my_sock:/tmp/my_sock \
    my_image

And let the framework create / use a socket file inside like /tmp/my_sock/example.sock, it works as expected.