how to deal with changing ips of docker compose containers?

Question

I've setup an app where a nodejs backend has to communicate with a rasa chatbot backend through a react frontend. All services are running through the same docker-compose. Being a docker beginner there are some things I'm not sure about:

communication between host and container is done using the container's ip

• browser opening the local react server running on localhost:3000 or 172.22.0.1:3000
• browser sending a request to the express backend on localhost:4000 172.22.0.2:4000

however communication between two docker containers is done is the container's name:

• rasa server conmmunicating with the rasa custom action server through http://action_server:5055/webhooks
• rasa custom action server communicating with the express backend through http://backend_name:4000/users/

my problem is that when I need to contact the rasa backend from my react front end I need to put the rasa docker container's ip which (sometimes) changes upon docker-compose reinitialization. To workaround this I do a docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' app_rasa_1 to get the ip and manually change it into the react frontend.

is there a way to avoid changing the ip alltogether and using the container name (or an alias/link) or what would be a way to automate the change of the container's ip in the react frontend (are environment variables updated via a script an option?)

Answer 1

Completely ignore the container-private IP addresses. They're implementation details that have several practical problems, including (as you note) them changing when a container is recreated. (They're also unreachable on non-Linux hosts, or if the browser isn't on the same host as the containers.)

You show the correct patterns in your question. For calls between containers, use the container names as host names (this setup is described more in Networking in Compose. For calls from outside containers, including from browser-based applications, use the host's DNS name or IP address and the first number from the ports: you publish.

If the browser application needs to contact a back-end server, it needs a path to do this. This could be via published ports:, or one of your other components could proxy the request to the service (maybe using the express-http-proxy middleware).

A dedicated container that only proxies to other backend services is also a useful pattern (Docker Nginx Proxy: how to route traffic to different container using path and not hostname includes some examples), particularly since this will let you use path-only URLs like /api or /rasa in your browser application. If the React application is served from http://localhost:8080/, and the main backend is http://localhost:8080/api, then you can just make HTTP requests to /api and they will be interpreted relative to the page's URL. This avoids the hostname problem completely, so long as your reverse proxy has path-based routes to every container you need to directly contact.