Docker Networking and Service Discovery¶

Port publishing maps a host-facing port to a container listener: browser → host port 8080 → Docker forwarding/NAT → container port 80 → Nginx.

Prefer a user-defined bridge for multi-container applications. Docker supplies DNS there, so an API should reach a database by a stable service name such as db, not a copied container IP. IPs may change when a container is recreated.

docker network inspect, docker port, DNS lookup, and application-level HTTP checks are the first troubleshooting tools. --network host removes normal network isolation and should be chosen deliberately.

Practice¶

docker network create app-net
docker run -d --name db --network app-net postgres:16
docker run --rm --network app-net busybox nslookup db
docker network inspect app-net

The nslookup command checks Docker-provided DNS resolution inside the same network. It does not prove that PostgreSQL is healthy or accepting the credentials your application uses.