Skip to main content

Ports & Networking

By default, Docker containers are isolated. Networking is the layer that allows them to communicate with each other, the host machine, and the outside world.

Docker Networking

1. Understanding Docker Networking Basics​

Docker uses network drivers to manage connectivity:

  • Bridge (Default): The standard driver for standalone containers. Containers on the same bridge can communicate, but to access them from outside, you must use port mapping.
  • Host: The container shares the host's networking namespace directly. There is no isolation.
  • None: Disables all networking for the container.

2. Port Mapping: Exposing Services​

Because containers are isolated, traffic from the outside world cannot reach them by default. Port mapping (or "publishing ports") acts as a bridge that forwards traffic from a specific port on your host machine to a port inside the container.

  • Command Syntax: Use the -p flag when running a container. 
    docker run -p <Host_Port>:<Container_Port> <Image_Name>
    Example: docker run -p 8080:80 nginx maps port 80 inside the container to port 8080 on your host.

3. Container-to-Container Communication​

When you have multiple containers that need to talk to each other, the best practice is to use User-Defined Bridge Networks instead of the default bridge.

  1. Create a custom network: docker network create my-app-net
  2. Attach containers to the network: docker run --network my-app-net ...
  3. Communicate by name: Because they are on the same user-defined network, your application can connect to the database simply by using the container name as the hostname.