ConfigMap 是一种 API 对象，用来将数据(非机密性)保存到键值对中；Pods 可以
   将其用作环境变量、命令行参数或者存储卷中的配置文件
实际工作中，可以将环境变量设置为引用 Kubernetes 集群中的公开服务，云端服务
   可以使用配置参数，本地调试也可以使用完全相同的代码    
微服务搭建过程中，通过编写configMap实现配置共享，提供更新配置效率及引用便捷

[root@k8smaster4 ~]# kubectl create configmap my-config --from-literal=tomcat_port=8080 --from-literal=tomcat_server=192.168.0.117

-----

[root@k8smaster4 ~]# kubectl get cm
NAME               DATA   AGE
kube-root-ca.crt   1      157d
my-config          2      6s
mysql-configmap    4      65d
[root@k8smaster4 ~]# kubectl describe cm my-config
Name:         my-config
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
tomcat_port:
----
8080
tomcat_server:
----
192.168.0.117

BinaryData
====

Events:  <none>
[root@k8smaster4 ~]#

[root@k8smaster4 cm]# kubectl create configmap my-config --from-file=www=/root/cm

[root@k8smaster4 cm]# kubectl create configmap my-config --from-file=/root/cm/nginx.conf

[root@k8smaster4 cm]# cat demo2.yaml 
apiVersion: v1
kind: Pod
metadata:
   name: my-nginx
   namespace: default
   labels:
     environment: test
     app: nginx-demo
     app.kubernetes.io/name: MyApp
spec:
  containers:
  - name: nginx-demo
    image: docker.io/library/nginx
    imagePullPolicy: IfNotPresent
    ports:
    - name: nginxport
      containerPort: 80
      protocol: TCP
    resources:
      requests:
        memory: "2Gi"
        cpu: "100m"
      limits:
        memory: "5Gi"
        cpu:  "200m"
    volumeMounts:
    - name: configmap
      mountPath: /etc/nginx
  volumes:
  - name: configmap
    configMap:
      name: my-nginx

---
apiVersion: v1
kind: Service
metadata:
  name: myservice
  namespace: default
  labels:
    app.kubernetes.io/name: myService
spec:
  selector:
    app.kubernetes.io/name: MyApp
  ports:
  - targetPort: 80
    port: 80
    protocol: TCP
    nodePort: 30009
  type: NodePort

[root@k8smaster4 cm]# kubectl edit cm my-nginx
configmap/my-nginx edited