etcd

This component is the distributed key-value store used by Kubernetes to store all cluster data. etcd is a consistent and highly-available key-value store used as Kubernetes' backing store for all cluster data.

Run the following command to check the status of the etcd cluster:

kubectl get pods -n kube-system -l component=etcd

$ kubectl get pods -n kube-system -l component=etcd -o wide --show-labels
NAME          READY   STATUS    RESTARTS   AGE     IP            NODE     NOMINATED NODE   READINESS GATES   LABELS
etcd-master   1/1     Running   0          4h24m   192.168.1.1   master   <none>           <none>            component=etcd,tier=control-plane

SSH into the etcd pod by running the following command:

kubectl exec -it etcd-master -n kube-system -- /bin/sh

Set the environment variables:

export ETCDCTL_API=3
export ETCDCTL_CACERT=/etc/kubernetes/pki/etcd/ca.crt
export ETCDCTL_CERT=/etc/kubernetes/pki/etcd/server.crt
export ETCDCTL_KEY=/etc/kubernetes/pki/etcd/server.key

View the Keys created for the Services in the etcd cluster, by running the following command:

etcdctl get /registry/services/specs --prefix --keys-only

Similarly, view the pods in the cluster by running the following command:

etcdctl get /registry/pods --prefix --keys-only

To view the data for each key, remove the --keys-only flag.

Here's the sample output:

$ kubectl exec -it etcd-master -n kube-system -- /bin/sh
sh-5.2#                                                                                                                                                                            
sh-5.2# export ETCDCTL_API=3
sh-5.2# export ETCDCTL_CACERT=/etc/kubernetes/pki/etcd/ca.crt
sh-5.2# export ETCDCTL_CERT=/etc/kubernetes/pki/etcd/server.crt
sh-5.2# export ETCDCTL_KEY=/etc/kubernetes/pki/etcd/server.key
sh-5.2# 
sh-5.2# etcdctl get /registry/services/specs --prefix --keys-only
/registry/services/specs/calico-apiserver/calico-api

/registry/services/specs/calico-system/calico-kube-controllers-metrics

/registry/services/specs/calico-system/calico-typha

/registry/services/specs/default/kubernetes

/registry/services/specs/kube-system/kube-dns
sh-5.2# 
sh-5.2# etcdctl get /registry/pods/ --prefix --keys-only    
/registry/pods/calico-apiserver/calico-apiserver-7cb798b74b-dmrx6

/registry/pods/calico-apiserver/calico-apiserver-7cb798b74b-s59cs

/registry/pods/calico-system/calico-kube-controllers-798d6c8f99-6mq5x

/registry/pods/calico-system/calico-node-gbxp7

/registry/pods/calico-system/calico-node-gpbrj

/registry/pods/calico-system/calico-node-wkjxt

/registry/pods/calico-system/calico-typha-65f8578fc5-8vshb

/registry/pods/calico-system/calico-typha-65f8578fc5-z5srw

/registry/pods/calico-system/csi-node-driver-6s4zr

/registry/pods/calico-system/csi-node-driver-7lqxb

/registry/pods/calico-system/csi-node-driver-kxp7r

/registry/pods/kube-system/coredns-7db6d8ff4d-792wd

/registry/pods/kube-system/coredns-7db6d8ff4d-nvxsf

/registry/pods/kube-system/etcd-master

/registry/pods/kube-system/kube-apiserver-master

/registry/pods/kube-system/kube-controller-manager-master

/registry/pods/kube-system/kube-proxy-9l64r

/registry/pods/kube-system/kube-proxy-svnvd

/registry/pods/kube-system/kube-proxy-zfvgt

/registry/pods/kube-system/kube-scheduler-master

/registry/pods/tigera-operator/tigera-operator-76ff79f7fd-2qddl

sh-5.2# 

Here, we can see the keys created for the resources like services and pods in the etcd. This component is crucial for the functioning of the Kubernetes cluster. Since every component in Kubernetes is stateless, the etcd provides a way to store the state of the cluster.