# Docker Ports

**Port mapping** connects container ports to host ports. Use `docker run -p <host>:<container>` to map. Multiple `-p` flags map multiple ports. `EXPOSE` is a Dockerfile instruction that documents ports but doesn't actually publish them. Containers on the same network reach each other by name without explicit port mapping.

```bash
$ docker run -p 8080:3000 myapp              # host port 8080 -> container port 3000
$ docker run -p 8080:3000 -p 9000:5000 myapp # map multiple ports
$ docker run -p 127.0.0.1:8080:3000 myapp    # bind to localhost only
$ docker port <container>                    # show port mappings
```

Port mapping is only needed to access the container from outside the host. If you're using Docker networks, containers can reach each other directly by service name without port mapping. `EXPOSE` in a Dockerfile is documentation only; it doesn't enforce port publishing. You must use `-p` at runtime to actually publish ports to the host.