Cannot Reach Container¶

Problem¶

One container cannot connect to another, or you cannot reach a container from your machine.

Symptoms¶

Errors such as:

could not resolve host
connection refused

Common Causes¶

• The containers are not on the same user-defined network
• The hostname used does not match the target container's name
• The containers are on the default bridge network, which has no name resolution
• The port was never published, so the host cannot reach it

Investigation¶

Check which network the containers are on.

docker network inspect my-net

Confirm the target container is running.

docker ps

Resolution¶

Put both containers on the same user-defined network, and use the target's container name as the hostname.

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

To reach a container from your own machine, publish its port with -p.

Prevention¶

• Always create a user-defined network for containers that talk to each other
• Match hostnames to container or service names exactly