this post was submitted on 14 Jul 2023
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Q: Docker container joining existing network with fixed ip (via docker compose) (lemmy.world)
submitted 1 year ago by Solvena@lemmy.world to c/selfhosted@lemmy.world
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Hi, I figured out how to get docker containers to join an existing network with putting "networks" into the respective sections of the docker-compose.yml

If I want to also give them fixed ip's on this network, what would the syntax look like in the docker-compose.yml?

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[–] cool_pebble@aussie.zone 9 points 1 year ago* (last edited 1 year ago) (1 children) 
networks:
  app:
    ipam:
      config:
        - subnet: 172.20.0.0/24
          gateway: 172.20.0.1
services:
  app:
    image: my-app-image
    networks:
      app:
        ipv4_address: 172.20.0.10

In the above example I've declared a Docker Bridge network with the range 172.20.0.0/24 and a gateway at 172.20.0.1. I have a service named app with a static IP of 172.20.0.10.

The same is also possible with IPv6, though there are extra steps involved to make IPv6 networking work in Docker and it's not enabled by default so I won't go into detail in this comment.

Out of curiosity, what's the use case for a static IP in the Docker Bridge network? Docker compose assigns hostnames equal to the service name. That is, if you had another container in the app network from my example above, it could just do a DNS lookup for app and it would resolve to 172.20.0.10.

[–] Solvena@lemmy.world 3 points 1 year ago (1 children)

thanky you, this looks like exactly what I need.

I do run several webservices (nextcloud, matrix) behind the same reverse proxy (nginx prxy manager). In my setup I have one docker with nginx running, which is the only one to be exposed to the web. It proxy-ing for the other services relies upon them being in the same network. It all works well, however I ran into problems when restarting my server after a shutdown. I suspect that some of the services tried to get the same ip adress as my nginx service, which results in that service not running properly and my whole reverse proxy setup falls apart at that point.

I'm not certain, that this is really what happens but I want to try and assign the fixed ip's and see if that solves the problem.

[–] cool_pebble@aussie.zone 2 points 1 year ago (1 children)

Honestly, I'd be surprised if static IPs fix it. Docker's default network type (bridge network) is very good at assigning IPs to containers without clashing, even with container restarts and replacements: it's been battle tested for years in production use. As others have said, standard DNS hostnames of containers should be sufficient. But I'll certainly be interested to hear your results.

[–] Solvena@lemmy.world 2 points 1 year ago* (last edited 1 year ago)

Edit: I fixed my problem by re-making my nginx reverse proxy and a do-over of my proxy hosts. I have yet to restart my server, though ...

I'm a beginner with all of this stuff, so I'm sure I'm not assessing correctly what's wrong with my setup. It's more of a methodical "trial and error" approach, that I have, where I change one thing at a time and see what happens ... quite time consuming but it helps me to figure things out along the way :)

However, if you have an idea, what could be wrong with my server, I'd appreciate any ideas: I run Nginx Reverse Proxy with nginx in a container within a custom network "my_network" and have assigned that container a fixed IP. I run other containers (portainer, mariadb, nextcloud, synapse) that all connect to the same custom network. The nginx container "see's" the outside web with ports 80 and 443 openend on the firewall for that container's fixed ip and routes traffic (and needed other ports) to my other containers. This is all working well and also works after restarting the server.

Now I tried to install a lemmy instance and got it up and running by bringing the lemmy containers in my custom network as well and proxy'img my nginx to the lemmy proxy. However, when I made a restart of the server, something broke and I cannot get the web-ui of NPM to load. I think somehow host names and/or IP adresses got mixed up somewhere. The containers start just fine, but I can't access it with web-ui anymore. Also reverse proxy-ing doesn't work, but if I open the needed ports on my firewall manually I can access the other services containers.

I hope this is even understandable, not sure if I'm using the correct terms ..