Docker: port is already allocated

In short: The host port the container should use is already occupied by another container or program.

In more detail: Message: Bind for 0.0.0.0:8080 failed: port is already allocated or address already in use. A port can be used by only one process at a time on a machine.

In Depth

Causes

• Another container runs with the same host port (-p 8080:80).
• A local program (for example development server, Nginx, local database) uses the port.
• An old container is still running or hanging (docker ps -a).
• Several Compose projects with identical ports.

Solutions

1. Check who occupies the port: docker ps (containers), ss -ltnp | grep 8080 or lsof -i :8080 (Linux/macOS), netstat -ano | findstr 8080 (Windows).
2. Stop/remove the old container: docker stop name && docker rm name, or in Compose docker compose down.
3. Choose another host port: -p 8081:80 (host left, container right).
4. Terminate the interfering program.
5. Check the ports entries in docker-compose.yml; within a network containers need no published ports, they address each other by name.

Note

Remember: -p HOST:CONTAINER. The container port may be 80 everywhere, the host port must be free. Publish ports only where necessary, and on servers only to 127.0.0.1 (-p 127.0.0.1:8080:80) so that they are not reachable from the network.

See also: EADDRINUSE, Docker, Docker volumes and networks