Setting the hostname for a container running in Kubernetes

Question

I want to set the hostname in a container running inside Kubernetes, but Kubernetes appears to be overriding whatever I set at runtime.

I've tried both setting /etc/hostname in the docker image I'm having Kubernetes use, and including echo "host.example.com > /etc/hostname" in the CMD in the Dockerfile.

There appears to be a docker flag -h to set the hostname. Is there a way for me to specify in my replication controller that it should start the container with a special flag?

The container's Debian, if it helps.

Answer 1

My previous answer was incorrect, edited with correct info

The -h flag for docker run will set the hostname of the container when you create it.

Test it out: docker run -h test.example.com -it ubuntu /bin/bash

The docker start command does not have the same -h or --hostname argument though. It doesn't seem possible to change the hostname of an existing container, just a new one from an image.

However w/r/t Kubernetes: There is an open issue on Github regarding how Kubernetes handles hostnames. It does not seem like Kubernetes exposes docker's hostname setting directly, but you might be able to influence it via your pod name

Answer 2

I found the answer for changing the docker hostname after the container has been running or I can say to the existing container here are some steps

1. Run

   docker inspect -f '{{ .State.Pid }}' <existing_docker_hostname> 

   Output will be a number <15580>

2. Run this command to login to the container

   nsenter --target 15580 --uts 

3. Run this command to change the hostname

   hostname "node_js" 

now exit the container and login again you will see the hostname has been changed.