[root@k8smaster4 sc]# echo -n 'admin' | base64
YWRtaW4=

[root@k8smaster4 sc]# echo -n '51cto' | base64
NTFjdG8=

[root@k8smaster4 sc]# cat secret-demo.yaml 
apiVersion: v1
kind: Secret
metadata:
  name: secret-opaque
  labels:
    environment: test
    app: myadmin
type: Opaque
data:
  username: YWRtaW4=
  password: NTFjdG8=

[root@k8smaster4 sc]# kubectl describe secret secret-opaque
Name:         secret-opaque
Namespace:    default
Labels:       app=myadmin
              environment=test
Annotations:  <none>

Type:  Opaque

Data
====
password:  5 bytes
username:  5 bytes

apiVersion: v1
kind: Pod
metadata:
  name: secret-volume
  labels:
    environment: test
    app: secret-volume-test
spec:
  containers:
  - name: secret-voluem-test
    image: docker.io/ikubernetes/myapp:v1
    imagePullPolicy: IfNotPresent
    volumeMounts:
    - name: secret-volume-demo
      readOnly: true
      mountPath: /etc/secret
  volumes:
  - secret:
      secretName: secret-opaque
    name: secret-volume-demo

[root@k8smaster4 sc]# kubectl exec -it secret-volume -c secret-voluem-test -- /bin/sh
/ # cd /etc/secret
/etc/secret # ls
password  username
/etc/secret # cat password 
/etc/secret # cat username