k8s基本概念-如何使用Services

k8s基本概念-如何使用Services

2018/1/5

Services 使用示例

• Virtual IPs and service proxies
• Publishing services - service types
• 經過命令行來控制 Service
• 經過 yaml 配置文件來定義 Service

Virtual IPs and service proxies

• Proxy-mode: userspace
  • 輪詢
• Proxy-mode: iptables
  • v1.2開始做爲默認選項
  • 比 userspace 快
  • 注意：若是一開始選擇的 pod 失去響應後，不能自動重試其餘 pod 於是須要定義 readiness probes
  • 隨機
• Proxy-mode: ipvs
  • FEATURE STATE: Kubernetes v1.9 beta
  • 比 iptables 快

Publishing services - service types

• ClusterIP
  • 建立一個 ClusterIP 來提供集羣內部訪問
  • 默認選項
• NodePort
  • 在每一個節點 IP 上暴露一個端口（NodePort）來提供服務，集羣外部經過這種方式來訪問：<NodeIP>:<NodePort>，同時會建立一個 ClusterIP
  • 這種類型使用較多
  • 默認暴露的隨機端口範圍：30000-32767
  • 能夠經過 nodePort 字段來顯式的指定端口
• LoadBalancer
  • 經過和 cloud provider’s load balancer 關聯使用，此時 NodePort and ClusterIP 將自動建立
• ExternalName
  • 將 service 名稱映射到一個 externalName （例如一個域名），經過 kube-dns 來提供 DNS 到 CNAME 記錄

經過命令行來控制 Service

• 獲取和建立 service

  ### 獲取全部的 service 列表：
  [root@tvm-00 ~]# kubectl get services
  NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
  kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   5d

建立一個網絡類型爲 NodePort 的 service 並暴露 pods 的 80 端口

[root@tvm-00 ~]# kubectl expose deployments/test-deployment-app-whoami --type="NodePort" --port 80
service "test-deployment-app-whoami" exposed

再次獲取全部的 service 列表：

[root@tvm-00 ~]# kubectl get services
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5d
test-deployment-app-whoami NodePort 10.108.8.154 <none> 80:31816/TCP 9s

固然，也能夠經過 label 來篩選：

[root@tvm-00 ~]# kubectl get services -l app=whoami
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
test-deployment-app-whoami NodePort 10.108.8.154 <none> 80:31816/TCP 23s

- 查看細節
```bash
### 查看 service 的細節：
[root@tvm-00 ~]# kubectl describe services/test-deployment-app-whoami
Name:                     test-deployment-app-whoami
Namespace:                default
Labels:                   app=whoami
Annotations:              <none>
Selector:                 app=whoami
Type:                     NodePort
IP:                       10.108.8.154
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
NodePort:                 <unset>  31816/TCP
Endpoints:                172.30.11.74:80,172.30.11.75:80,172.30.11.77:80 + 2 more...
Session Affinity:         None
External Traffic Policy:  Cluster
Events:                   <none>

### 此處也能夠經過 label 來篩選
[root@tvm-00 ~]# kubectl describe services -l app=whoami
Name:                     test-deployment-app-whoami
Namespace:                default
Labels:                   app=whoami
Annotations:              <none>
Selector:                 app=whoami
Type:                     NodePort
IP:                       10.108.8.154
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
NodePort:                 <unset>  31816/TCP
Endpoints:                172.30.11.74:80,172.30.11.75:80,172.30.11.77:80 + 2 more...
Session Affinity:         None
External Traffic Policy:  Cluster
Events:                   <none>

• 請求 service

  [root@tvm-00 ~]# export NODE_PORT=$(kubectl get services/test-deployment-app-whoami -o go-template='{{(index .spec.ports 0).nodePort}}')
  [root@tvm-00 ~]# echo NODE_PORT=$NODE_PORT
  NODE_PORT=31816

[root@tvm-00 ~]# kubectl get pods -l app=whoami
NAME READY STATUS RESTARTS AGE
test-deployment-app-whoami-6cf9cd6bf4-2dd5m 1/1 Running 0 15h
test-deployment-app-whoami-6cf9cd6bf4-bb7v7 1/1 Running 0 15h
test-deployment-app-whoami-6cf9cd6bf4-c7cht 1/1 Running 0 15h
test-deployment-app-whoami-6cf9cd6bf4-jhtqz 1/1 Running 0 15h
test-deployment-app-whoami-6cf9cd6bf4-px24h 1/1 Running 0 15h

測試請求 10 次的結果：

[root@tvm-00 ~]# for i in $(seq 1 10); do curl -s tvm-00:$NODE_PORT|grep Hostname; done
Hostname: test-deployment-app-whoami-6cf9cd6bf4-jhtqz
Hostname: test-deployment-app-whoami-6cf9cd6bf4-bb7v7
Hostname: test-deployment-app-whoami-6cf9cd6bf4-px24h
Hostname: test-deployment-app-whoami-6cf9cd6bf4-jhtqz
Hostname: test-deployment-app-whoami-6cf9cd6bf4-2dd5m
Hostname: test-deployment-app-whoami-6cf9cd6bf4-c7cht
Hostname: test-deployment-app-whoami-6cf9cd6bf4-c7cht
Hostname: test-deployment-app-whoami-6cf9cd6bf4-bb7v7
Hostname: test-deployment-app-whoami-6cf9cd6bf4-jhtqz
Hostname: test-deployment-app-whoami-6cf9cd6bf4-px24h

符合預期，請求隨機分佈在 5 個 pods 上

- 刪除 service
```bash
[root@tvm-00 ~]# kubectl delete services -l app=whoami
service "test-deployment-app-whoami" deleted
[root@tvm-00 ~]# kubectl get services
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   5d

經過 yaml 配置文件來定義 Service

• 建立配置文件

  [root@tvm-00 ~]# cat ~/k8s_install/test/whoami/app.yaml
  apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
  kind: Deployment
  metadata:
  name: app-whoami
  labels:
  app: whoami
  spec:
  replicas: 3
  selector:
  matchLabels:
    app: whoami
  template:
  metadata:
    labels:
      app: whoami
  spec:
    containers:
      - name: whoami
        image: opera443399/whoami:0.9
        ports:
          - containerPort: 80

---

apiVersion: v1
kind: Service
metadata:
name: svc-whoami
labels:
app: whoami
spec:
selector:
app: whoami
ports:

• protocol: TCP
  port: 80
  targetPort: 80
  nodePort: 30080
  type: NodePort

- 執行
```bash
[root@tvm-00 ~]# kubectl apply -f whoami/app.yaml --record
deployment "app-whoami" created
service "svc-whoami" created

• 獲取信息

  [root@tvm-00 ~]# kubectl get all -l app=whoami
  NAME                DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
  deploy/app-whoami   3         3         3            3           25s

NAME DESIRED CURRENT READY AGE
rs/app-whoami-6cf9cd6bf4 3 3 3 25s

NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
deploy/app-whoami 3 3 3 3 25s

NAME DESIRED CURRENT READY AGE
rs/app-whoami-6cf9cd6bf4 3 3 3 25s

NAME READY STATUS RESTARTS AGE
po/app-whoami-6cf9cd6bf4-2pxlh 1/1 Running 0 25s
po/app-whoami-6cf9cd6bf4-82ng2 1/1 Running 0 25s
po/app-whoami-6cf9cd6bf4-msbmk 1/1 Running 0 25s

NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
svc/svc-whoami NodePort 10.96.100.22 <none> 80:30080/TCP 25s

- 測試
```bash
[root@tvm-00 ~]# curl -s 10.96.100.22:80 |grep Hostname
Hostname: app-whoami-6cf9cd6bf4-msbmk
[root@tvm-00 ~]# curl -s tvm-00:30080 |grep Hostname
Hostname: app-whoami-6cf9cd6bf4-2pxlh
[root@tvm-00 ~]# curl -s tvm-01:30080 |grep Hostname
Hostname: app-whoami-6cf9cd6bf4-2pxlh
[root@tvm-00 ~]# curl -s tvm-02:30080 |grep Hostname
Hostname: app-whoami-6cf9cd6bf4-msbmk