core_dns stuck in ContainerCreating status - kubernetes

Question

I am trying to setup a basic k8s cluster
After doing a kubeadm init --pod-network-cidr=10.244.0.0/16, the coredns pods are stuck in ContainerCreating status
NAME READY STATUS RESTARTS AGE
coredns-6955765f44-2cnhj 0/1 ContainerCreating 0 43h
coredns-6955765f44-dnphb 0/1 ContainerCreating 0 43h
etcd-perf1 1/1 Running 0 43h
kube-apiserver-perf1 1/1 Running 0 43h
kube-controller-manager-perf1 1/1 Running 0 43h
kube-flannel-ds-amd64-smpbk 1/1 Running 0 43h
kube-proxy-6zgvn 1/1 Running 0 43h
kube-scheduler-perf1 1/1 Running 0 43h
OS-IMAGE: Ubuntu 16.04.6 LTS
KERNEL-VERSION: 4.4.0-142-generic
CONTAINER-RUNTIME: docker://19.3.5
Errors from journalctl -xeu kubelet command
Jan 02 10:31:44 perf1 kubelet[11901]: 2020-01-02 10:31:44.112 [INFO][10207] k8s.go 228: Using Calico IPAM
Jan 02 10:31:44 perf1 kubelet[11901]: E0102 10:31:44.118281 11901 cni.go:385] Error deleting kube-system_coredns-6955765f44-2cnhj/12cd9435dc905c026bbdb4a1954fc36c82ede1d703b040a3052ab3370445abbf from
Jan 02 10:31:44 perf1 kubelet[11901]: E0102 10:31:44.118828 11901 remote_runtime.go:128] StopPodSandbox "12cd9435dc905c026bbdb4a1954fc36c82ede1d703b040a3052ab3370445abbf" from runtime service failed:
Jan 02 10:31:44 perf1 kubelet[11901]: E0102 10:31:44.118872 11901 kuberuntime_manager.go:898] Failed to stop sandbox {"docker" "12cd9435dc905c026bbdb4a1954fc36c82ede1d703b040a3052ab3370445abbf"}
Jan 02 10:31:44 perf1 kubelet[11901]: E0102 10:31:44.118917 11901 kuberuntime_manager.go:676] killPodWithSyncResult failed: failed to "KillPodSandbox" for "e44bc42f-0b8d-40ad-82a9-334a1b1c8e40" with
Jan 02 10:31:44 perf1 kubelet[11901]: E0102 10:31:44.118939 11901 pod_workers.go:191] Error syncing pod e44bc42f-0b8d-40ad-82a9-334a1b1c8e40 ("coredns-6955765f44-2cnhj_kube-system(e44bc42f-0b8d-40ad-
Jan 02 10:31:47 perf1 kubelet[11901]: W0102 10:31:47.081709 11901 cni.go:331] CNI failed to retrieve network namespace path: cannot find network namespace for the terminated container "747c3cc9455a7d
Jan 02 10:31:47 perf1 kubelet[11901]: 2020-01-02 10:31:47.113 [INFO][10267] k8s.go 228: Using Calico IPAM
Jan 02 10:31:47 perf1 kubelet[11901]: E0102 10:31:47.118526 11901 cni.go:385] Error deleting kube-system_coredns-6955765f44-dnphb/747c3cc9455a7db202ab14576d15509d8ef6967c6349e9acbeff2207914d3d53 from
Jan 02 10:31:47 perf1 kubelet[11901]: E0102 10:31:47.119017 11901 remote_runtime.go:128] StopPodSandbox "747c3cc9455a7db202ab14576d15509d8ef6967c6349e9acbeff2207914d3d53" from runtime service failed:
Jan 02 10:31:47 perf1 kubelet[11901]: E0102 10:31:47.119052 11901 kuberuntime_manager.go:898] Failed to stop sandbox {"docker" "747c3cc9455a7db202ab14576d15509d8ef6967c6349e9acbeff2207914d3d53"}
Jan 02 10:31:47 perf1 kubelet[11901]: E0102 10:31:47.119098 11901 kuberuntime_manager.go:676] killPodWithSyncResult failed: failed to "KillPodSandbox" for "52ffb25e-06c7-4cc6-be70-540049a6be20" with
Jan 02 10:31:47 perf1 kubelet[11901]: E0102 10:31:47.119119 11901 pod_workers.go:191] Error syncing pod 52ffb25e-06c7-4cc6-be70-540049a6be20 ("coredns-6955765f44-dnphb_kube-system(52ffb25e-06c7-4cc6-
I have tried kubdeadm reset as well but no luck so far

Answer 1

Looks like the issue was because I tried switching from calico to flannel cni. Following the steps mentioned here has resolved the issue for me
Pods failed to start after switch cni plugin from flannel to calico and then flannel
Additionally you may have to clear the contents of /etc/cni/net.d

Answer 2

CoreDNS will not start up before a CNI network is installed.
For flannel to work correctly, you must pass --pod-network-cidr=10.244.0.0/16 to kubeadm init.
Set /proc/sys/net/bridge/bridge-nf-call-iptables to 1 by running sysctl net.bridge.bridge-nf-call-iptables=1 to pass bridged IPv4 traffic to iptables’ chains. This is a requirement for some CNI plugins to work.
Make sure that your firewall rules allow UDP ports 8285 and 8472 traffic for all hosts participating in the overlay network. see here .
Note that flannel works on amd64, arm, arm64, ppc64le and s390x under Linux. Windows (amd64) is claimed as supported in v0.11.0 but the usage is undocumented
To deploy flannel as CNI network
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/2140ac876ef134e0ed5af15c65e414cf26827915/Documentation/kube-flannel.yml
After you have deployed flannel delete the core dns pods, Kubernetes will recreate the pods.

Answer 3

You have deployed flannel as CNI but the logs from kubelet shows that kubernetes is using calico.
[INFO][10207] k8s.go 228: Using Calico IPAM
Something wrong with container network. without that coredns doesnt succeed.
You might have to reinstall with correct CNI. Once CNI is deployed successfully, coreDNS gets deployed automatically

Answer 4

So here is my solution:
First, coreDNS will run on your [Master / Control-Plane] Nodes
Now let's run ifconfig to check for these 2 interfaces cni0 and flannel.1
Suppose cni0=10.244.1.1 & flannel.1=10.244.0.0 then your DNS will not be created
It should be cni0=10.244.0.1 & flannel.1=10.244.0.0. Which mean cni0 must follow flannel.1/24 patterns
Run the following 2 command to Down Interface and Remove it from your Master/Control-Plane Machines
sudo ifconfig cni0 down;
sudo ip link delete cni0;
Now check via ifconfig you will see 2 more vethxxxxxxxx Interface appears. This should fixed your problem.