创建一个Service资源后，他会自动创建出一个同名的Endpoint资源。因为Service并不直接匹配其后端的标签，而是交由Endpoint进行匹配，而匹配过程是由Endpoint控制器完成的。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
# 查看系统上存在的SVC
root@k8s-master01:~# kubectl get svc
NAME                       TYPE           CLUSTER-IP      EXTERNAL-IP    PORT(S)        AGE
demoapp                    NodePort       10.111.8.128    <none>         80:31156/TCP   7d
demoapp-externalip-svc     ClusterIP      10.96.141.139   172.16.11.75   80/TCP         12h
demoapp-loadbalancer-svc   LoadBalancer   10.98.79.128    <pending>      80:30373/TCP   12h
demoapp-service-nodeport   NodePort       10.97.56.1      <none>         80:31398/TCP   15h
demoapp-svc                ClusterIP      10.97.72.1      <none>         80/TCP         16h
kubernetes                 ClusterIP      10.96.0.1       <none>         443/TCP        7d14h

# 查看EP
root@k8s-master01:~# kubectl get ep
NAME                       ENDPOINTS                                               AGE
demoapp                    10.244.1.4:80,10.244.2.3:80,10.244.3.2:80 + 1 more...   7d
demoapp-externalip-svc     10.244.1.4:80,10.244.2.3:80,10.244.3.2:80 + 1 more...   12h
demoapp-loadbalancer-svc   10.244.1.4:80,10.244.2.3:80,10.244.3.2:80 + 1 more...   12h
demoapp-service-nodeport   10.244.1.4:80,10.244.2.3:80,10.244.3.2:80 + 1 more...   15h
demoapp-svc                10.244.1.4:80,10.244.2.3:80,10.244.3.2:80 + 1 more...   16h
kubernetes                 172.16.11.71:6443                                       7d14h

# 对比SVC和EP可以发现他们的名字相同

Endpoint资源还与就绪探针存在关联关系，只有就绪后，才会被Endpoint捕获并添加为可用的后端端点。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
root@k8s-master01:~# kubectl describe ep demoapp-svc
Name:         demoapp-svc
Namespace:    default
Labels:       <none>
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2021-07-05T09:35:54Z
Subsets:
  Addresses:          10.244.1.4,10.244.2.3,10.244.3.2,172.16.11.81   # 此处为已经就绪的端点
  NotReadyAddresses:  <none>   # 此处为未就绪的端点。
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

Events:  <none>

# 所有未就绪的后端端点不会被Service接受流量。

未就绪状态演示

1.编写配置清单

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
apiVersion: v1
kind: Service
metadata:
  name: service-readiness-demo
  namespace: default
spec:
  selector:
    app: demoapp-with-readiness
  ports:
  - name: http
    port: 80
    targetPort: 80
    protocol: TCP
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: demoapp2
spec:
  replicas: 2
  selector:
    matchLabels:
      app: demoapp-with-readiness
  template:
    metadata:
      labels:
        app: demoapp-with-readiness
    spec:
      containers:
      - name: demoapp
        image: ikubernetes/demoapp:v1.0
        imagePullPolicy: IfNotPresent
        readinessProbe:
          httpGet:
            path: '/readyz'
            port: 80
          initialDelaySeconds: 15
          periodSeconds: 10

2.应用配置清单

1
2
3
4
5
6
7
8
root@k8s-master01:~# kubectl apply -f service-readiness-demo.yaml 
service/service-readiness-demo created
deployment.apps/demoapp2 created

root@k8s-master01:~# kubectl get pods -l app=demoapp-with-readiness -o wide
NAME                        READY   STATUS    RESTARTS   AGE     IP            NODE         NOMINATED NODE   READINESS GATES
demoapp2-5b5dc85587-p6l58   1/1     Running   0          8m21s   10.244.3.27   k8s-node03   <none>           <none>
demoapp2-5b5dc85587-wtht9   1/1     Running   0          8m21s   10.244.3.26   k8s-node03   <none>           <none>

3.查看endpoint

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
root@k8s-master01:~# kubectl describe ep service-readiness-demo 
Name:         service-readiness-demo
Namespace:    default
Labels:       <none>
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2021-07-06T02:25:54Z
Subsets:
  Addresses:          10.244.3.26,10.244.3.27
  NotReadyAddresses:  <none>
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

Events:  <none>

# 两个后端端点已经就绪

4.手动的将其中一个pod改为非ready状态

1
2
3
root@k8s-master01:~# curl -XPOST -d 'readyz=FAIL' 10.244.3.26/readyz
root@k8s-master01:~# curl 10.244.3.26/readyz
FAIL

5.再次查看endpoint

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
root@k8s-master01:~# kubectl describe ep service-readiness-demo 
Name:         service-readiness-demo
Namespace:    default
Labels:       <none>
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2021-07-06T02:37:44Z
Subsets:
  Addresses:          10.244.3.27
  NotReadyAddresses:  10.244.3.26
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

Events:  <none>

# 此时10.244.3.26已经成为notReady状态。流量不会被Service引入

6.对Service进行请求

1
2
3
4
5
6
7
8
9
10
11
12
13
14
# 获取service地址
root@k8s-master01:~# kubectl get svc service-readiness-demo 
NAME                     TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
service-readiness-demo   ClusterIP   10.97.181.65   <none>        80/TCP    14m

# 对Service进行访问，只会被调度到10.244.3.27
root@k8s-master01:~# curl 10.97.181.65
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: demoapp2-5b5dc85587-p6l58, ServerIP: 10.244.3.27!
root@k8s-master01:~# curl 10.97.181.65
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: demoapp2-5b5dc85587-p6l58, ServerIP: 10.244.3.27!
root@k8s-master01:~# curl 10.97.181.65
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: demoapp2-5b5dc85587-p6l58, ServerIP: 10.244.3.27!
root@k8s-master01:~# curl 10.97.181.65
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: demoapp2-5b5dc85587-p6l58, ServerIP: 10.244.3.27!

7.让后端端点变为就绪

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
root@k8s-master01:~# curl -XPOST -d 'readyz=OK' 10.244.3.26/readyz

# 再次查看ep的详细信息，所由端点都已经就绪
root@k8s-master01:~# kubectl describe ep service-readiness-demo
Name:         service-readiness-demo
Namespace:    default
Labels:       <none>
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2021-07-06T02:49:54Z
Subsets:
  Addresses:          10.244.3.26,10.244.3.27
  NotReadyAddresses:  <none>
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

Events:  <none>

8.访问SVC

1
2
3
4
5
# 后端端点可以被轮询调度
root@k8s-master01:~# curl 10.97.181.65
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: demoapp2-5b5dc85587-wtht9, ServerIP: 10.244.3.26!
root@k8s-master01:~# curl 10.97.181.65
iKubernetes demoapp v1.0 !! ClientIP: 10.244.0.0, ServerName: demoapp2-5b5dc85587-p6l58, ServerIP: 10.244.3.27!