Why is my Docker Compose setup failing to connect between services on different networks?

All answers to this question.

Docker Compose creates a default network for all services listed in the file. Each service can reach others using their service name as the hostname. The "connection refused" error usually isn't a DNS issue; it typically means the backend service isn't listening on the port you think it is, or it hasn't finished starting up. Ensure your backend is listening on 0.0.0.0 instead of 127.0.0.1. Inside a container, 127.0.0.1 refers to the container itself, not the network. If your web app tries to hit 127.0.0.1, it will fail because the API isn't inside the web container.

   Answered 2025-06-15 by Margaret King

Have you verified that your backend service has a proper "healthcheck" defined so the frontend only attempts to connect once the API is fully ready to receive traffic?

   Answered 2025-06-25 by Richard Hill

• Richard, healthchecks are great but "depends_on" is also needed. However, "depends_on" only waits for the container to start, not the application. Adding a "wait-for-it.sh" script is a more robust way to ensure the database or API is actually listening before the frontend boots.

     Commented 2025-06-28 by Joseph Allen

Check your port mappings. Remember that internal container-to-container communication uses the internal port, not the one you mapped to your host machine in the ports section.

   Answered 2025-07-05 by Susan Green

• This is such a common mistake for beginners. Susan is spot on; keep the internal ports consistent across your service environment to avoid these networking headaches.

     Commented 2025-07-10 by Thomas Wright