Connect Containers¶

When to Use This Guide¶

Use this guide to let two containers talk to each other, for example an app container reaching a database container.

docker run -d --name app --network my-net my-app

Step 1: Create a Shared Network¶

docker network create my-net

Step 2: Run Both Containers On It¶

Start each container with --network my-net.

docker run -d --name db --network my-net postgres:16
docker run -d --name app --network my-net my-app

Step 3: Reach One From the Other by Name¶

The app container can now reach the database using the hostname db, its container name. No IP addresses needed.

Connect an Existing Container¶

If a container is already running, attach it to a network without restarting it.

docker network connect my-net existing-container

Common Issues¶

"could not resolve host"

Both containers must be on the same user-defined network, and the hostname must match the target container's name exactly.

Name resolution not working on the default bridge

The built-in bridge network has no name discovery. Always create your own network for this.

Related Guides¶

• Create a Network
• Expose Ports