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Exposing docker socket to a container (discuss.tchncs.de)
submitted 1 year ago by to c/selfhosted@lemmy.world
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Do you guys expose the docker socket to any of your containers or is that a strict no-no? What are your thoughts behind it if you don't? How do you justify this decision from a security standpoint if you do?

I am still fairly new to docker but I like the idea of something like Watchtower. Even though I am not a fan of auto-updates and I probably wouldn't use that feature I still find it interesting to get a notification if some container needs an update. However, it needs to have access to the docker socket to do its work and I read a lot about that and that this is a bad idea which can result in root access on your host filesystem from within a container.

There are probably other containers as well especially in this whole monitoring and maintenance category, that need that privilege, so I wanted to ask how other people handle this situation.

Cheers!

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[–] [S] 1 point 1 year ago (4 children)

I have heard the name Kubernetes and know that is also some kind of container thing, but never went really deeper than that. It was more a general question how people handle the whole business of exposing the docker socket to a container. Since I came across it in Watchtower and considered installing that I used it as an example. I always thought that Kubernetes and Docker swarms and things like that are something for the future when I have more experience with Docker and containers in general, but thank you for the idea.

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  • [–] 2 points 1 year ago (3 children)

    I've seen three cases where the docker socket gets exposed to the container (perhaps there are more but I haven't seen any?):

    1. Watchtower, which does auto updates and/or notifies people

    2. Nextcloud AIO, which uses a management container that controls the docker socket to deploy the rest of the stuff nextcloud wants.

    3. Traefik, which reads the docker socket to automatically reverse proxy services.

    Nextcloud does the AIO, because Nextcloud is a complex service, but it grows to be very complex if you want more features or performance. The AIO handles deploying all the tertiary services for you, but something like this is how you would do it yourself: https://github.com/pimylifeup/compose/blob/main/nextcloud/signed/compose.yaml . Also, that example docker compose does not include other services, like collabara office, which is the google docs/sheets/slides alternative, a web based office.

    Compare this to the kubernetes deployment, which yes, may look intimidating at first. But actually, many of the complexities that the docker deploy of nextcloud has are automated away. Enabling the Collabara office is just collabara.enabled: true in the configuration of it. Tertiary services like Redis or the database, are included in the Kubernetes package as well. Instead of configuring the containers itself, it lets you configure the database parameters via yaml, and other nice things.

    For case 3, Kubernetes has a feature called an "Ingress", which is essentially a standardized configuration for a reverse proxy that you can either separate out, or one is provided as part of the packages. For example, the nextcloud kubernetes package I linked above, has a way to handle ingresses in the config.

    Kubernetes handles these things pretty well, and it's part of why I switched. I do auto upgrade, but I only auto upgrade my services, within the supported stable release, which is compatible for auto upgrades and won't break anything. This enables me to get automatic security updates for a period of time, before having to do a manual and potentially breaking upgrade.

    TLDR: You are asking questions that Kubernetes has answers to.

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  • [–] [S] 1 point 1 year ago (2 children)

    Thanks for the write-up and sorry for the late reply. I guess I didn't come very far without exposing the docker socket. Nextcloud was actually one of the services on my list I wanted to try out. But I haven't looked at the compose file yet. It makes sense why it is needed by the AIO image. Interestingly, it uses a Docker socket proxy to presumably also mitigate some of the security risks that come from exposing the socket. Just like another comment in this thread already mentioned.

    However, since I don't know much about Kubernetes I can't really tell if it improves something, or if the privileges are just shifted e.g. from the container having socket access to the Kubernetes orchestration thingy having socket access. But it looks indeed interesting and maybe it is not a bad idea to look into it even early on in my selfhost and container adventure.

    Even though I said otherwise in another comment, I think I have also seen socket access in Nginx Proxy Manager in some example now. I don't really know the advantages other than that you are able to use the container names for your proxy hosts instead of IP and port. I have also seen it in a monitoring setup, where I think Prometheus has access to the socket to track different Docker/Container statistics.

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  • [–] 1 point 1 year ago (1 child)

    I think I have also seen socket access in Nginx Proxy Manager in some example now. I don't really know the advantages other than that you are able to use the container names for your proxy hosts instead of IP and port

    I don't think you need socket access for this? This is what I did: https://stackoverflow.com/questions/31149501/how-to-reach-docker-containers-by-name-instead-of-ip-address#35691865

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  • [–] [S] 1 point 1 year ago

    Yeah, you are right a custom bridge network can do DNS resolution with container names. I just saw in a video from Lawrence Systems, that he exposed the socket. And somewhere else I saw that container names where used for the proxy hosts in NPM. Since the default bridge doesn't do DNS resolution I assumed that is why some people expose the socket.

    I just checked again and apparently he created the compose file with ChatGPT which added the socket. https://forums.lawrencesystems.com/t/nginx-proxy-manager-docker/24147/6 I always considered him to be one of the more trustworthy and also security conscious people out there, but this makes me question his authority. Atleast he corrected the mistake, so everyone who actually uses his compose file now doesn't expose the socket.

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