Worker node unable to join master node in kubernetes - kubernetes

Question

I have two network interface in my master node -
192.168.56.118
10.0.3.15
While doing kubeadm init on master node, I got following command to add workers
kubeadm join --token qr1czu.5lh1nt34ldiauc1u 192.168.56.118:6443 --discovery-token-ca-cert-hash sha256:e5d90dfa0fff67589551559c443762dac3f1e5c7a5d2b4a630e4c0156ad0e16c
As you can see, it shows 192.168.56.118 IP to connect from worker.
But while executing the same on worker node, I'm getting following error.
[root#k8s-worker ~]# kubeadm join --token qr1czu.5lh1nt34ldiauc1u 192.168.56.118:6443 --discovery-token-ca-cert-hash sha256:e5d90dfa0fff67589551559c443762dac3f1e5c7a5d2b4a630e4c0156ad0e16c
[preflight] Running pre-flight checks
[discovery] Trying to connect to API Server "192.168.56.118:6443"
[discovery] Created cluster-info discovery client, requesting info from "https://192.168.56.118:6443"
[discovery] Requesting info from "https://192.168.56.118:6443" again to validate TLS against the pinned public key
[discovery] Failed to request cluster info, will try again: [Get https://192.168.56.118:6443/api/v1/namespaces/kube-public/configmaps/cluster-info: x509: certificate is valid for 10.96.0.1, 10.0.3.15, not 192.168.56.118]
I tried with other IP - 10.0.3.15. But it returns connection refused error, despite the fact that the firewall is disabled in master.
[root#k8s-worker ~]# kubeadm join --token qr1czu.5lh1nt34ldiauc1u 10.0.3.15:6443 --discovery-token-ca-cert-hash sha256:e5d90dfa0fff67589551559c443762dac3f1e5c7a5d2b4a630e4c0156ad0e16c
[preflight] Running pre-flight checks
[WARNING Service-Kubelet]: kubelet service is not enabled, please run 'systemctl enable kubelet.service'
[discovery] Trying to connect to API Server "10.0.3.15:6443"
[discovery] Created cluster-info discovery client, requesting info from "https://10.0.3.15:6443"
[discovery] Failed to request cluster info, will try again: [Get https://10.0.3.15:6443/api/v1/namespaces/kube-public/configmaps/cluster-info: dial tcp 10.0.3.15:6443: connect: connection refused]
How can I force the certificate to make 192.168.56.118 as valid? or any idea how can I resolve this issue?

Answer 1

You need to provide extra apiserver certificate SAN (--apiserver-cert-extra-sans <ip_address>) and api server advertise address(--apiserver-advertise-address) while initialising the cluster using kubeadm init. Your kubeadm init command will look like:
kubeadm init --apiserver-cert-extra-sans 192.168.56.118 --apiserver-advertise-address 192.168.56.118
Once, you initialise cluster with above command you will not face the issue of certificates while joining the cluster