September 2, 2016 · Ubuntu kubernetes dns

Kubernetes local-up-cluster - dns fixes on Ubuntu

So as it turns out I didn't get too far beyond the local kubernetes install without running into some issues. The first being the lack of DNS (I wanted to run the amazing dashboard UI) and then port forwarding to access pod functionality directly.

Ubuntu prerequisites

As it turns out there are a number of Ubuntu 14.04 specific hurdles to overcome before kubernetes will work happily.

First of all dnsmasq needs to be disabled so comment it out and restart networking services via the following

sudo nano /etc/NetworkManager/NetworkManager.conf  
sudo restart network-manager  

Find out more about dnsmasq and ubuntu here

Next the tools socat and nsenter are required for kubernetes port forwarding.
To install socat run

sudo apt-get install socat  

To install nsenter is slightly more work due to lack of 14.04 support but not much thanks to the work of Jérôme Petazzoni.

docker run --rm jpetazzo/nsenter cat /nsenter > /tmp/nsenter && chmod +x /tmp/nsenter  
sudo cp /tmp/nsenter /usr/local/bin  

Check out the repo here or this gist if you want to go step by step

To find out more about socat here and nsenter here

Back to kubernetes

After these steps it's hopefully smooth sailing. So lets start kubernetes with DNS on by default by running the following

export API_HOST=`ifconfig docker0 | grep "inet addr" | awk -F'[: ]+' '{ print $4 }'`  

Instructions for validating your DNS setup can be found here

Let's add the dashboard

kubectl create -f  

This can be accessed via


From this you can view and manage most things you can via the kubectl cli.

Kind of gotcha but not really

One thing to note is that when you terminate the kubernetes process all the docker containers remain running (see docker ps). This at first caused concern, but then remember kubernetes is designed so that the containers it manages are themselves not dependent on kubernetes to function. If the scheduler dies, the containers are unaffected, only scheduling. This is a consistent philosophy throughout the kubernetes system and makes sense that upon shutdown would not remove all running containers. A few properties to note
1. If kubernetes is subsequently spun up it will reconcile the state of the system with desired state. As you would expect
2. Other docker containers can be spun up and down locally & independent of those managed by kubernetes.
These properties are possible due to docker labels being applied by kubernetes to the containers it manages.