Expose Ports¶

When to Use This Guide¶

Use this guide to make a container reachable from your own machine or the outside world, by publishing one of its ports.

Quick Command

docker run -d -p 8080:80 nginx

Step 1: Publish a Port¶

Map a port on your host to a port inside the container.

docker run -d -p 8080:80 --name web nginx

The format is -p HOST:CONTAINER. Here host port 8080 connects to container port 80.

Step 2: Access It¶

curl http://localhost:8080

Publish Multiple Ports¶

Repeat -p for each port you need.

docker run -d -p 8080:80 -p 8443:443 --name web nginx

EXPOSE vs Publishing¶

A EXPOSE line in a Dockerfile only documents which port an app uses. It does not open it. Only -p at run time actually publishes a port to the host.

Common Issues¶

"port is already allocated"

Another process is using that host port. Pick a different one, such as -p 8081:80.

Reachable from the container network but not the host

You did not publish the port. Add -p to make it reachable from your machine.