Kubernetes worker node staying in "NotReady" state - kubernetes

Question

I have two node Kubernetes setup in Virtualbox. Master is up and running fine. But the worker node is staying in "NotReady" state.
[root#master ~]# kubectl get nodes
NAME STATUS ROLES AGE VERSION
master Ready master 1d v1.10.2
node NotReady <none> 1h v1.10.2
"journalctl -u kubelet" command on worker node is reporting networking related errors:
kuberuntime_manager.go:757] checking backoff for container "install-cni" in pod "kube-flannel-ds-zjlvn_kube-system(873fa36d-4b83-11e8-9997-080027afb5ab)"
remote_runtime.go:278] ContainerStatus "459643e54de7f82df8ada0f60e8f3d51d42c5ce348747a66e20ad5720155e63f" from runtime service failed: rpc error: code = U
kuberuntime_container.go:636] failed to remove pod init container "install-cni": failed to get container status "459643e54de7f82df8ada0f60e8f3d51d42c5ce34
kuberuntime_manager.go:757] checking backoff for container "install-cni" in pod "kube-flannel-ds-zjlvn_kube-system(873fa36d-4b83-11e8-9997-080027afb5ab)"
kuberuntime_manager.go:767] Back-off 10s restarting failed container=install-cni pod=kube-flannel-ds-zjlvn_kube-system(873fa36d-4b83-11e8-9997-080027afb5a
pod_workers.go:186] Error syncing pod 873fa36d-4b83-11e8-9997-080027afb5ab ("kube-flannel-ds-zjlvn_kube-system(873fa36d-4b83-11e8-9997-080027afb5ab)"), sk
cni.go:171] Unable to update cni config: No networks found in /etc/cni/net.d
kubelet.go:2125] Container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni con
cni.go:171] Unable to update cni config: No networks found in /etc/cni/net.d
kubelet.go:2125] Container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni con
cni.go:171] Unable to update cni config: No networks found in /etc/cni/net.d
kubelet.go:2125] Container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni con
I am running Kubernetes version 1.10 and docker version 1.13.1. Could you please help me identify the root cause and resolution for this issue?

Answer 1

Well the thing is, when you want to form a kubernetes cluster, it requires that you deploy a CNI plugin which would provide networking between your pods. The error that you have shown here is due to a CNI plugin not being installed or not being configured properly.
The kube-dns pod would be in pending state until the CNI plugin is deployed on your cluster. Once kube-dns moves to a running state, (after deploying the cni provider) you can run your application workloads.
If you have not deployed a CNI plugin, there are several ones you can choose from.
Calico: Provides Pod networking via standard BGP. (Follow the documentation for further info)
kubectl apply -f https://docs.projectcalico.org/v3.1/getting-started/kubernetes/installation/hosted/kubeadm/1.7/calico.yaml
Weave: Creates an overlay network.
export kubever=$(kubectl version | base64 | tr -d '\n')
kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$kubever"
Flannel: Creates an overlay network treating each host as a subnet.
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/v0.9.1/Documentation/kube-flannel.yml
Container traffic needs to be made aware to the iptables and you can do that by
sysctl net.bridge.bridge-nf-call-iptables=1
This is required by Flannel and Weave to function.
Please do refer to the documentation of each CNI plugin which would be suitable for your cluster.