How Docker Port Mapping Connects Containers to Your Host Machine

Docker containers run in isolated environments with their own private networks, making them inaccessible to applications on the host machine by default. To bridge this gap, Docker uses a mechanism called port mapping, which creates a defined route between a host port and a container port using the format Host Port:Container Port. This allows, for example, a Node.js app on the host to communicate with a PostgreSQL database running inside a container on port 5432. If a port conflict exists on the host, a different host port such as 5433 can be mapped to the container's 5432, with the container remaining unaware of the change. Beyond connectivity, explicit port mapping enforces the principle of least privilege by keeping all unmapped container ports locked down and inaccessible from outside.