follow-up/Dockerization.md

@@ -2,6 +2,16 @@ Dockerizing the project is challenging because of two things:
 1. the classpath setup done in [start_component.sh](/implementation/start_component.sh)
 2. the GPIO pins of the Raspberry Pi must be accessible from inside the container for the lights
 
+## Prior consideration: Network
+Docker and docker-compose make setting up a container stack really easy. 
+But there is a huge drawback: mDNS resolution won't work from inside a container.
+But as components like lights register their address as `hostname.local` in the registry and server mDNS resolution is needed.
+
+There are 3 ways to get around this problem:
+1. Don't use Docker. It makes the setup easier but setting up a working network may take too much time for your use case.
+2. Use a fixed network configuration. This would need to be set in the router *and must be changed in the code*, so components register with their IP.
+3. Use [this tool](https://github.com/hardillb/dns-to-mdns) and run it on any of the Pis. It needs to run on port 53 as you can't set a port in the configuration for Docker. You have to start your containers with the `--dns <IP of mDNS resolver>` flag (or the entry in the `docker-compose.yml`. This is only necessary for containers of components that need to call functions on other components (like the server or the light controller).
+
 ## Dockerfile Walkthrough
 The Dockerfile is used to build the container.
 It holds instructions on which files to copy and commands to run.