Expose port

2 snippets in Docker

DKDocker

Port Mapping (-p)

syntax

docker run -p <host_port>:<container_port> <image>
docker run -p <host_ip>:<host_port>:<container_port> <image>

example

docker run -d -p 8080:3000 myapp:1.0
docker run -d -p 127.0.0.1:5432:5432 postgres:16

Note The format is always host:container. Binding to 127.0.0.1 restricts access to localhost only — critical for databases you do not want exposed on the network. Without an IP, Docker binds to 0.0.0.0 (all interfaces).

EXPOSE — Document Container Port

DK · Dockerfile

syntax

EXPOSE <port>[/<protocol>]

example

EXPOSE 3000
EXPOSE 8443/tcp

Note EXPOSE is documentation only — it does NOT publish the port. You still need -p at runtime. Think of it as a note to anyone reading the Dockerfile about which ports the application listens on.