introduction

In this article I will cover the quick setup of a self-hosted Kubernetes 1.9 cluster using kubeadm, with the ability to recover after a power cycle (e.g., reboot)

I started playing around with kubeadm again for a new project and was especially interested in the self-hosting feature, which is in alpha state. In short, self-hosted clusters host their control plane (api-server, controller-manager, scheduler) as a workload. Compared to the universe of compilers, self-hosting is when a compiler can correctly compile the source code of itself. In term of kubernetes, this simplifies upgrading clusters to a new version and more in-depth monitoring

quick setup

Consider we have three nodes where kubernetes should be installed. Each node should have internet connectivity and meet the requirements mentioned in the install guide.

Let’s say; the nodes are node1, node2, and node3. For a quick setup of docker and kubeadm, ssh on each node as root and run:

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$ wget -cO- https://gist.githubusercontent.com/xetys/0ecfa01790debb2345c0883418dcc7c4/raw/2bcd7f42ce4c51d21b33e84aadc6438979e50286/ubuntu16-kubeadm | bash -

Then on node1:

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$ kubeadm init --pod-network-cidr=192.168.0.0/16 --feature-gates=SelfHosting=true
$ mkdir -p $HOME/.kube
$ cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
$ chown $(id -u):$(id -g) $HOME/.kube/config
$ kubectl apply -f https://docs.projectcalico.org/v2.6/getting-started/kubernetes/installation/hosted/kubeadm/1.6/calico.yaml

On node2 and node3 run:

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$ kubeadm join --token <token> <master-ip>:<master-port> --discovery-token-ca-cert-hash sha256:<hash>

With the values from the output of the kubeadm init command. This is a quick setup for a self-hosted kubernetes with calico networking.

make it recoverable

Currently, a reboot would cause a total failure of the cluster, as no new control plane is scheduled, and kubelet won’t reach the API server. To fix this, run:

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$ git clone https://github.com/xetys/k8s-self-hosted-recovery
$ cd k8s-self-hosted-recovery
$ ./install.sh

This will install a systemd service, which runs after the kubelet.service and a script k8s-self-hosted-recover, which does the following to recover a self-hosted control plane after reboot:

• perform the controlplane phase of kubeadm to setup the plane using static pods
• wait until the API server is working
• delete the DaemonSet of the current self-hosted control plane
• run the selfhosted phase of kubeadm

Congratulations, you have a three-node kubernetes 1.9 self-hosted cluster!

Enjoy!

Sources:

• Docker + kubeadm install
• k8s-self-hosted-recover GitHub