1 to 3 masters

Cluster state:

1 master: master01.fqdn 2 workers: worker01.fqdn, worker01.fqdn

A couple of nginx pods are running.

Goal:

Add a new load balancer in order to add 2 masters.

The fqdn of the load balancer is lb.fqdn

Step 1 - Add future load balancer fqdn to the apiServercertSANs in ClusterConfiguration

In the file cluster/kubeadm-init.conf and in the ConfigMap kubesystem/kubeadm-config:

---
apiServer:
  certSANs:
  - master01.fqdn

Add fqdn and IP to the list:

---
apiServer:
  certSANs:
  - master01.fqdn
  - lb.fqdn.fqdn
  - IP.lb

Step 2 - Regenerate certs on master with kubeadm so the apiserver can be contact with the fqdn of the LB

⚠️ It is required to restart the apiserver once the certificates are renewed, this obviously means a short downtime.

On master01.fqdn:

Check the current DNS configured in the certificates:

openssl x509 -noout -text -in  /etc/kubernetes/pki/apiserver.crt|grep DNS

Backup current certificates:

mkdir /root/backup
mv /etc/kubernetes/pki/apiserver.{crt,key} /root/backup

Copy kubeadm-init.conf on the node, e.g /root/kubeadm-init.conf.

Renew certificates:

kubeadm init phase certs apiserver --config /root/kubeadm-init.yaml -v5

Validate the new FQDN of the LB is now in the certificate.

openssl x509 -noout -text -in  /etc/kubernetes/pki/apiserver.crt|grep DNS

Restart apiserver:

crictl ps|grep kube-apiserver| awk '{ print $1 }'
crictl stop f3293429ddc6a && crictl rm f3293429ddc6a

Step 3 - Validate the apiserver can be contacted through the new LB

$ curl https://lb.fqdn.fqdn:6443
{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {
    
  },
  "status": "Failure",
  "message": "forbidden: User \"system:anonymous\" cannot get path \"/\"",
  "reason": "Forbidden",
  "details": {
    
  },
  "code": 403
}

Step 4 - Update controlPlaneEndpoint in ClusterConfiguration with the fqdn of the LB, (probably somewhere as well in the skuba-config)

In the file cluster/kubeadm-init.conf and in the ConfigMap kube-system/kubeadm-config:

apiServer:
  certSANs:
  - master01.fqdn
  - lb.fqdn.fqdn
  - IP.lb
  extraArgs:
    oidc-issuer-url: https://master01.fqdn:32000
controlPlaneEndpoint: master01.fqdn:6443

To:

apiServer:
  certSANs:
  - master01.fqdn
  - lb.fqdn.fqdn
  - IP.lb
  extraArgs:
    oidc-issuer-url: https://lb.fqdn:32000
controlPlaneEndpoint: lb.fqdn:6443

In the following ConfigMaps, replace all occurence of master01.fqdn with lb.fqdn.fqdn:

• kube-system/cluster-info
• kube-system/oidc-dex-config
• kube-system/oidc-gangway-config
• kube-system/kube-proxy

5. Update workers

Drain node:

kubectl drain worker01 --ignore-daemonsets

Connect to the node worker01.

Replace master fqdn with lb fqdn in /etc/kubernetes/kubelet.conf

apiVersion: v1
clusters:
- cluster:
    server: https://lb.fqdn.fqdn:6443

Restart kubelet.

systemctl restart kubelet

Uncordon node:

kubectl uncordon worker01

Step 6 - Clean kubeadm config from master01

Remove occurences of master01.fqdn in cluster/kubeadm-init.conf and in the ConfigMap kube-system/kubeadm-config

Replace all occurences in the cluster file directory. e.g

find . -type f -exec sed -i 's/master01\.fqdn/lb\.fqdn\.fqdn/' {} +

Step 7 - Add 2 new masters to the cluster

skuba node join --role master --user sles --sudo --target

Step 8 - Restart kube-proxy

Recreate kube-proxy pods so they can use the LB instead of contacting master01 directly. Deleting the pods will recreate the pod with the configmap we have edited previously.

kubectl -n kube-system rollout restart ds/kube-proxy

Step 9 - Restart DEX and GANGWAY

⚠️ Short downtime for external connection.

Recreate gangway and dex pods so they can use the LB instead of contacting master01 directly. Deleting the pods will recreate the pod with the configmap we have edited previously.

kubectl -n kube-system rollout restart deploy/oidc-gangway
kubectl -n kube-system rollout restart deploy/oidc-dex

Step 10 - Replace fqdn everywhere else

Update the kubeconfig, ConfigMap, scripts, CI etc to use the new LB.

Step 11 - Update master01

⚠️ At this stage, nothing should be using master01.fqdn directly.

Repeat the step 2, this will remove master01.fqdn from the apiserver certificate.

openssl x509 -noout -text -in  /etc/kubernetes/pki/apiserver.crt|grep DNS

--> fqdn of the master01 should not be in the list.

Remove occurences of master01.fqdn in /etc/kubernetes

find . -type f -exec sed -i 's/master01\.fqdn/lb\.fqdn\.fqdn/' {} +