还有就是今天要聊的是，Kubernetes 1.19.0——服务svc(2)

一个pod如何访问到另外一个应用程序的svc

[root@vms61 chap9-svc]# kubectl run blog --image=hub.c.163.com/library/mysql:latest --image-pull-policy=IfNotPresent --env="MYSQL_ROOT_PASSWORD=redhat"
pod/blog created
[root@vms61 chap9-svc]# kubectl run blog --image=hub.c.163.com/library/wordpress:latest --image-pull-policy=IfNotPresent --env="WORDPRESS_DB_HOST=XXXXX" --env="WORDPRESS_DB_USER=root" --env="WORDPRESS_DB_PASSWORD=redhat" --dry-run=client -o yaml > blog.yaml

[root@vms61 chap9-svc]# kubectl get svc
NAME   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
db     ClusterIP   10.100.102.138   <none>        3306/TCP   136m
[root@vms61 chap9-svc]# cat blog.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: blog
  name: blog
spec:
  containers:
  - env:
    - name: WORDPRESS_DB_HOST
      value: 10.100.102.138
    - name: WORDPRESS_DB_USER
      value: root
    - name: WORDPRESS_DB_PASSWORD
      value: redhat
    image: hub.c.163.com/library/wordpress:latest
    imagePullPolicy: IfNotPresent
    name: blog
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
[root@vms61 chap9-svc]# kubectl apply -f blog.yaml 
pod/blog created
[root@vms61 chap9-svc]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
blog   1/1     Running   0          7s

创建一个svc，通过32178访问，会直接跳过数据库设置

[root@vms61 chap9-svc]# kubectl expose --name=blog pod blog --port=80 --type=NodePort
service/blog exposed
[root@vms61 chap9-svc]# kubectl get svc
NAME   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
blog   NodePort    10.98.75.125     <none>        80:32178/TCP   4s
db     ClusterIP   10.100.102.138   <none>        3306/TCP       142m

如果通过变量的方式：
1.只能获取相同namespace里的变量 
2.变量的获取有先后顺序，引用的变量必须要先创建

通过变量的方式发现

[root@vms61 chap9-svc]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
db     1/1     Running   0          28m
[root@vms61 chap9-svc]# cat blog.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: blog
  name: blog
spec:
  containers:
  - env:
    - name: WORDPRESS_DB_HOST
      value: $(DB_SERVICE_HOST)
    - name: WORDPRESS_DB_USER
      value: root
    - name: WORDPRESS_DB_PASSWORD
      value: redhat
    image: hub.c.163.com/library/wordpress:latest
    imagePullPolicy: IfNotPresent
    name: blog
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
[root@vms61 chap9-svc]# kubectl apply -f blog.yaml 
pod/blog created
[root@vms61 chap9-svc]# kubectl get pods
NAME   READY   STATUS    RESTARTS   AGE
blog   1/1     Running   0          2s
db     1/1     Running   0          28m
[root@vms61 chap9-svc]# kubectl get svc
NAME   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
blog   NodePort    10.107.97.68    <none>        80:31462/TCP   2m57s
db     ClusterIP   10.105.66.169   <none>        3306/TCP       27m

效果是一样的

通过DNS的方式发现—推荐

在kube-system里有dns，可以自动发现所有命名空间里的服务的clusterIP

所以，在同一个命名空间里，一个服务访问另外一个服务的时候，可以直接通

过服务名来访问

只要创建了一个服务(不管在哪个ns里创建的)，都会自动向kube-system里的

DNS注册

如果是不同的命名空间，可以通过服务名.命名空间名来访问

服务名.命名空间.svc.cluster.local

直接将value写成db服务名，可通过dns自动解析到

[root@vms61 chap9-svc]# cat blog.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: blog
  name: blog
spec:
  containers:
  - env:
    - name: WORDPRESS_DB_HOST
      value: db
    - name: WORDPRESS_DB_USER
      value: root
    - name: WORDPRESS_DB_PASSWORD
      value: redhat
    image: hub.c.163.com/library/wordpress:latest
    imagePullPolicy: IfNotPresent
    name: blog
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
[root@vms61 chap9-svc]# kubectl apply -f blog.yaml 
pod/blog created
[root@vms61 chap9-svc]# kubectl get pods
NAME                    READY   STATUS    RESTARTS   AGE
blog                    1/1     Running   0          3s
db                      1/1     Running   0          64m
web1-6464d54bd7-dxz7x   1/1     Running   0          19m
web1-6464d54bd7-ktbfr   1/1     Running   0          19m
web1-6464d54bd7-m4qg5   1/1     Running   0          19m
[root@vms61 chap9-svc]# kubectl get svc
NAME   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
db     ClusterIP   10.105.66.169    <none>        3306/TCP   63m
svc1   ClusterIP   10.108.124.206   <none>        80/TCP     10m
[root@vms61 chap9-svc]# kubectl expose --name=blog pod blog --port=80 --type=NodePort
service/blog exposed
[root@vms61 chap9-svc]# kubectl get svc
NAME   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
blog   NodePort    10.110.42.125    <none>        80:31672/TCP   3s
db     ClusterIP   10.105.66.169    <none>        3306/TCP       65m
svc1   ClusterIP   10.108.124.206   <none>        80/TCP         11m

依旧能达到如上效果