Ports and Volumes

Publish a port

Containers have their own network namespace. -p maps a host port to a container port so browsers and tools on your machine can connect.

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

Why volumes matter

Files written only inside a container disappear when that container is removed. A volume or bind mount stores data on the host or in Docker-managed storage.

Bind-mount a folder

This example serves files from a local site directory. Paths must exist on the host.

mkdir -p site
echo '<h1>Hello from a volume</h1>' > site/index.html
docker run -d --name static -p 8081:80 \
  -v "$(pwd)/site:/usr/share/nginx/html:ro" nginx

Name a volume

Named volumes are handy for databases. Docker creates and manages the storage location.

docker volume create app-data
docker run -d --name db \
  -e POSTGRES_PASSWORD=secret \
  -v app-data:/var/lib/postgresql/data \
  postgres:16