update_ip.sh

#!/bin/bash
set -e

# update IP addresses in configs in k8s and on kind master node
# * this is ugly, but the only way to avoid recreating the cluster after restart
export PATH=$PATH:/usr/local/bin

if [ -z "$1" ]; then
  echo "Usage: $0 <kind-cluster-name>"
  exit 1
fi

kube_context=kind-$1
docker_prefix=$1
update_cert=./update_cert.sh

# check connectivity, fail silently if not reachable
kubectl --context=$kube_context cluster-info --request-timeout=3 > /dev/null 2>&1

# 1. get configured 'advertiseAddress'
config_ip=$(kubectl -n kube-system --context=$kube_context get configmap kubeadm-config -o json \
  | jq '.data.ClusterStatus' | sed -e 's/.*advertiseAddress: \([0-9.]\+\)\\n.*/\1/')
#data:
#  ClusterStatus: |
#    apiEndpoints:
#      rootk8s-stage-control-plane:
#        advertiseAddress: 172.19.0.8
#        bindPort: 6443

# 2. get current master node IP
master_ip=$(kubectl -n kube-system --context=$kube_context get nodes -l node-role.kubernetes.io/master -o json \
  | jq '.items[0].status.addresses[]|select(.type == "InternalIP")|.address' | tr -d \")

# IPs differ -> we need to update
if [ "$config_ip" != "$master_ip" ]; then
  echo "Configured IP '$config_ip' does not match master IP '$master_ip' : updating config"

  # 1. configmap
  cluster_status=$(kubectl -n kube-system --context=$kube_context get configmap kubeadm-config -o json \
    | jq '.data.ClusterStatus' | sed -e "s/advertiseAddress: [0-9.]\+\\\\n/advertiseAddress: $master_ip\\\\n/")
  patch_data='{ "data": { "ClusterStatus": '$cluster_status' }}'
  kubectl -n kube-system --context=$kube_context patch configmap kubeadm-config --type merge --patch "$patch_data"

  # 2. config master node
  docker exec -t ${docker_prefix}-control-plane sed -i -e "s/$config_ip:6443/$master_ip:6443/" /etc/kubernetes/scheduler.conf
  docker exec -t ${docker_prefix}-control-plane sed -i -e "s/$config_ip:6443/$master_ip:6443/" /etc/kubernetes/controller-manager.conf

  # 3. update API certificate IPs
  $update_cert $docker_prefix $config_ip $master_ip
fi