Upgrade a kubeadm powered Kubernetes cluster on AWS EC2

Like any other software, Kubernetes reveals some security breaches from time to time. On November 26th, 2018 CVE-2018-1002105 was published with a critical score of 9,8 (10 is maximum).

With a specially crafted request, users that are authorized to establish a connection through the Kubernetes API server to a backend server can then send arbitrary requests over the same connection directly to that backend, authenticated with the Kubernetes API server’s TLS credentials used to establish the backend connection.

Every team running one of the following Kubernetes version, should update immediately:

  • Kubernetes v1.0.x-1.9.x
  • Kubernetes v1.10.0-1.10.10 (fixed in v1.10.11)
  • Kubernetes v1.11.0-1.11.4 (fixed in v1.11.5)
  • Kubernetes v1.12.0-1.12.2 (fixed in v1.12.3)

In our case, we decided to upgrade to v1.11.6.

For a good reason, kubeadm, kubelet and kubectl won’t be updated automatically by the system’s package manager (line 6):

$ cat /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
exclude=kube*
gpgcheck=1
repo_gpgcheck=0
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg

We need to add a small switch to the yum update command to run an update on those three packages:

yum update -y kubelet kubeadm kubectl --disableexcludes=kubernetes

Let me add a small note here. If you’ve set custom KUBELET_EXTRA_ARGS in /etc/sysconfig/kubelet, check it after the above update has been done. The kubelet RPM package has still an issue on that.

After package update has been done, proceed to step 2:

kubeadm upgrade plan

This does some pre update checks. If everything finishes without errors, we can start the actual upgrade with step 3:

kubeadm upgrade apply v1.11.6

Don’t worry if this takes some time and if you see some timeout errors.

Afterwards, kubeadm tells you that the upgrade succeeded successfully (hopefully).

Let’s do some post upgrade tasks:

systemctl daemon-reload
systemctl restart kubelet

Wait some seconds and continue with an update of your CNI (Container Network Interface). This step highly depends on which CNI you’re using. In our case (calico), we need to do:

$ kubectl apply -f https://docs.projectcalico.org/v3.3/getting-started/kubernetes/installation/hosted/rbac-kdd.yaml

clusterrole.rbac.authorization.k8s.io/calico-node configured
clusterrolebinding.rbac.authorization.k8s.io/calico-node configured

and

$ kubectl apply -f https://docs.projectcalico.org/v3.3/getting-started/kubernetes/installation/hosted/kubernetes-datastore/calico-networking/1.7/calico.yaml

configmap/calico-config unchanged
service/calico-typha unchanged
deployment.apps/calico-typha configured
poddisruptionbudget.policy/calico-typha unchanged
daemonset.extensions/calico-node configured
serviceaccount/calico-node unchanged
customresourcedefinition.apiextensions.k8s.io/felixconfigurations.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/bgppeers.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/bgpconfigurations.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/ippools.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/hostendpoints.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/clusterinformations.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/globalnetworkpolicies.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/globalnetworksets.crd.projectcalico.org configured
customresourcedefinition.apiextensions.k8s.io/networkpolicies.crd.projectcalico.org configured

That’s it. We ready with our master node.

Our nodes need to be updated, too. Start with draining a node from the master:

$ kubectl drain ip-10-10-12-70.eu-central-1.compute.internal --ignore-daemonsets --delete-local-data

Switch to the node now and run the system’s package upgrade:

$ yum update kubelet-1.11.6-0 kubeadm-1.11.6-0 kubectl-1.11.6-0 --disableexcludes=kubernetes

Then upgrade the node configuration:

$ kubeadm upgrade node config --kubelet-version $(kubelet --version | cut -d ' ' -f 2)

and restart kubelet:

systemctl daemon-reload
systemctl restart kubelet

Finally, don’t forget to “undrain” the freshly updated node from the master again:

$ kubectl uncordon ip-10-10-12-70.eu-central-1.compute.internal

That’s it again.

Check your node’s version and verify that all pods, daemonsets etc. are running.

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