Service Discovery

Kubernetes 服务的自动发现。

源码 https://github.com/xiaopeng163/flask-redis

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: redis-server
  template:
    metadata:
      labels:
        app: redis-server
    spec:
      containers:
        - name: redis-server
          image: redis:latest
          command:
            - redis-server
            - --requirepass
            - redis
          ports:
            - containerPort: 6379
---
apiVersion: v1
kind: Service
metadata:
  name: redis
spec:
  selector:
    app: redis-server
  ports:
    - protocol: TCP
      port: 6379
      targetPort: 6379

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: flask-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: flask-app
  template:
    metadata:
      labels:
        app: flask-app
    spec:
      containers:
        - name: flask-app
          image: xiaopeng163/flask-redis
          ports:
            - containerPort: 5000
          env:
            - name: REDIS_HOST
              value: ????????????????????????
---
apiVersion: v1
kind: Service
metadata:
  name: flask-service
spec:
  selector:
    app: flask-app
  ports:
    - protocol: TCP
      port: 8000
      targetPort: 5000

DNS

(国内无法访问google的朋友，请替换下面image为 xiaopeng163/hello-app:1.0)

$ kubectl create deployment demo --image=gcr.io/google-samples/hello-app:1.0 --port=8080
$ kubectl expose deployment demo

这时不仅有一个clusterIP可供整个cluster访问，同时一个DNS域名也被注册了（类似前面讲过的POD）。

我们可以在集群节点上访问以下域名，（当然要指定DNS server是coredns的地址）

$ kubectl get svc --namespace kube-system
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
kube-dns   ClusterIP   10.96.0.10   <none>        53/UDP,53/TCP,9153/TCP   37d
$ nslookup demo.default.svc.cluster.local 10.96.0.10
Server:             10.96.0.10
Address:    10.96.0.10#53

Name:       demo.default.svc.cluster.local
Address: 10.105.71.223

也就是 <service name>.<namespace>.svc.cluster.local

如果在创建一个pod，在pod里可以访问到demo这个service以及后面的deployment

$ kubectl run client --image=xiaopeng163/net-box --command -- sh -c "sleep 100000"
$ kubectl exec -it client -- sh
/omd # nslookup demo.default.svc.cluster.local
;; Truncated, retrying in TCP mode.
Server:             10.96.0.10
Address:    10.96.0.10#53

Name:       demo.default.svc.cluster.local
Address: 10.105.71.223

/omd # curl demo.default.svc.cluster.local:8080
Hello, world!
Version: 1.0.0
Hostname: demo-557f884dd8-7n55c
/omd #

ENV

另外一些环境变量也会在集群内注册。这时候如果我们创建另外一个POD

$ kubectl run client --image=xiaopeng163/net-box --command -- sh -c "sleep 100000"
$ kubectl exec -it client -- sh
/omd # env | grep DEMO
DEMO_SERVICE_HOST=10.105.71.223
DEMO_PORT_8080_TCP_ADDR=10.105.71.223
DEMO_PORT_8080_TCP_PORT=8080
DEMO_PORT_8080_TCP_PROTO=tcp
DEMO_PORT=tcp://10.105.71.223:8080
DEMO_SERVICE_PORT=8080
DEMO_PORT_8080_TCP=tcp://10.105.71.223:8080