[root@k8s-master ~]# cd /etc/kubernetes/pki/
[root@k8s-master pki]# ls
apiserver.crt                 apiserver-kubelet-client.key  devuser.kubeconfig  front-proxy-client.crt
apiserver-etcd-client.crt     ca.crt                        devuser.pem         front-proxy-client.key
apiserver-etcd-client.key     ca.key                        etcd                sa.key
apiserver.key                 devuser.csr                   front-proxy-ca.crt  sa.pub
apiserver-kubelet-client.crt  devuser-key.pem               front-proxy-ca.key
[root@k8s-master pki]# openssl x509 -in apiserver.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 8026942590652842542 (0x6f656dc1f451022e)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=kubernetes
        Validity
            Not Before: Jan 28 08:20:48 2020 GMT
            Not After : Jan 27 08:20:48 2021 GMT
...
...省略
...
[root@k8s-master pki]# openssl x509 -in ca.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 0 (0x0)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=kubernetes
        Validity
            Not Before: Jan 28 08:20:48 2020 GMT
            Not After : Jan 25 08:20:48 2030 GMT