Kubernetes 系列一 Access Applications in a Cluster by Publishing Services

Concepts

For some parts of your application (e.g. frontends) you may want to expose a Service onto an external (outside of your cluster) IP address.

Kubernetes ServiceTypes allow you to specify what kind of service you want. The default is ClusterIP.

Type values and their behaviors are:

ClusterIP: Exposes the service on a cluster-internal IP. Choosing this value makes the service only reachable from within the cluster. This is the default ServiceType.
NodePort: Exposes the service on each Node’s IP at a static port (the NodePort). A ClusterIP service, to which the NodePort service will route, is automatically created. You’ll be able to contact the NodePort service, from outside the cluster, by requesting :.
LoadBalancer: Exposes the service externally using a cloud provider’s load balancer. NodePort and ClusterIP services, to which the external load balancer will route, are automatically created.
ExternalName: Maps the service to the contents of the externalName field (e.g. foo.bar.example.com), by returning a CNAME record with its value. No proxying of any kind is set up. This requires version 1.7 or higher of kube-dns.

Hands on Practice

Create an External Load Balancer to Access an Application in a Cluster

[test@demotest nginx_kube_example]$ kubectl run hello-world --replicas=2 --labels="run=load-balancer-example" --image=gcr.io/google-samples/node-hello:1.0  --port=8080
deployment.apps "hello-world" created
 
[test@demotest nginx_kube_example]$ kubectl get pods --selector="run=load-balancer-example"
NAME                          READY     STATUS        RESTARTS   AGE
hello-world-58f9949f8-hchpz   1/1       Running       0          5s
hello-world-58f9949f8-wfdcf   1/1       Running       0          5s
[test@demotest nginx_kube_example]$ kubectl expose deployment hello-world --type=LoadBalancer  --name=example-service
service "example-service" exposed
 
[test@demotest nginx_kube_example]$ kubectl get services example-service
NAME              TYPE           CLUSTER-IP    EXTERNAL-IP   PORT(S)          AGE
example-service   LoadBalancer   10.96.52.33   <pending>     8080:30166/TCP   5s
[test@demotest nginx_kube_example]$ kubectl get services example-service
NAME              TYPE           CLUSTER-IP    EXTERNAL-IP      PORT(S)          AGE
example-service   LoadBalancer   10.96.52.33   129.146.88.108   8080:30166/TCP   34s
 
[test@demotest nginx_kube_example]$ curl http://129.146.88.108:8080
Hello Kubernetes!
 
[test@demotest nginx_kube_example]$ kubectl describe svc example-service-lb
Name:                     example-service-lb
Namespace:                default
Labels:                   run=load-balancer-example
Annotations:              <none>
Selector:                 run=load-balancer-example
Type:                     LoadBalancer
IP:                       10.96.81.181
LoadBalancer Ingress:     129.146.155.148
Port:                     <unset>  8080/TCP
TargetPort:               8080/TCP
NodePort:                 <unset>  32507/TCP
Endpoints:                10.244.0.165:8080,10.244.1.30:8080
Session Affinity:         None
External Traffic Policy:  Cluster
Events:
  Type    Reason                Age              From                Message
  ----    ------                ----             ----                -------
  Normal  EnsuringLoadBalancer  1m (x2 over 2m)  service-controller  Ensuring load balancer
  Normal  EnsuredLoadBalancer   1m (x2 over 1m)  service-controller  Ensured load balancer
[test@demotest nginx_kube_example]$ kubectl delete svc example-service-lb
service "example-service-lb" deleted
[test@demotest nginx_kube_example]$ kubectl delete deployment hello-world
deployment.extensions "hello-world" deleted

Use NodePort to Access an Application in a Cluster

[test@demotest nginx_kube_example]$ kubectl run hello-world --replicas=2 --labels="run=load-balancer-example" --image=gcr.io/google-samples/node-hello:1.0  --port=8080
deployment.apps "hello-world" created
 
[test@demotest nginx_kube_example]$ kubectl get deployments hello-world
NAME          DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
hello-world   2         2         2            2           7s
[test@demotest nginx_kube_example]$ kubectl describe deployments hello-world
Name:                   hello-world
Namespace:              jx
CreationTimestamp:      Thu, 28 Jun 2018 01:56:48 +0000
Labels:                 run=load-balancer-example
Annotations:            deployment.kubernetes.io/revision=1
Selector:               run=load-balancer-example
Replicas:               2 desired | 2 updated | 2 total | 2 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  1 max unavailable, 1 max surge
Pod Template:
  Labels:  run=load-balancer-example
  Containers:
   hello-world:
    Image:        gcr.io/google-samples/node-hello:1.0
    Port:         8080/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
OldReplicaSets:  <none>
NewReplicaSet:   hello-world-58f9949f8 (2/2 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  14s   deployment-controller  Scaled up replica set hello-world-58f9949f8 to 2
   
   
[test@demotest nginx_kube_example]$ kubectl get replicasets
NAME                    DESIRED   CURRENT   READY     AGE
hello-world-58f9949f8   2         2         2         24s
 
[test@demotest nginx_kube_example]$ kubectl describe replicasets
Name:           hello-world-58f9949f8
Namespace:      jx
Selector:       pod-template-hash=149550594,run=load-balancer-example
Labels:         pod-template-hash=149550594
                run=load-balancer-example
Annotations:    deployment.kubernetes.io/desired-replicas=2
                deployment.kubernetes.io/max-replicas=3
                deployment.kubernetes.io/revision=1
Controlled By:  Deployment/hello-world
Replicas:       2 current / 2 desired
Pods Status:    2 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  pod-template-hash=149550594
           run=load-balancer-example
  Containers:
   hello-world:
    Image:        gcr.io/google-samples/node-hello:1.0
    Port:         8080/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                   Message
  ----    ------            ----  ----                   -------
  Normal  SuccessfulCreate  29s   replicaset-controller  Created pod: hello-world-58f9949f8-bg7pk
  Normal  SuccessfulCreate  29s   replicaset-controller  Created pod: hello-world-58f9949f8-sbrzx
   
   
[test@demotest nginx_kube_example]$ kubectl expose deployment hello-world --type=NodePort --name=example-service
service "example-service" exposed
[test@demotest nginx_kube_example]$ kubectl describe services example-service
Name:                     example-service
Namespace:                jx
Labels:                   run=load-balancer-example
Annotations:              <none>
Selector:                 run=load-balancer-example
Type:                     NodePort
IP:                       10.96.70.43
Port:                     <unset>  8080/TCP
TargetPort:               8080/TCP
NodePort:                 <unset>  32322/TCP
Endpoints:                10.244.0.151:8080,10.244.1.16:8080
Session Affinity:         None
External Traffic Policy:  Cluster
Events:                   <none>
 
[test@demotest nginx_kube_example]$ kubectl get pods --selector="run=load-balancer-example" --output=wide
NAME                          READY     STATUS    RESTARTS   AGE       IP             NODE
hello-world-58f9949f8-bg7pk   1/1       Running   0          1m        10.244.0.151   129.146.112.202
hello-world-58f9949f8-sbrzx   1/1       Running   0          1m        10.244.1.16    129.146.135.107
[test@demotest nginx_kube_example]$ curl http://129.146.112.202:32322
Hello Kubernetes!
[test@demotest nginx_kube_example]$ curl http://129.146.135.107:32322
Hello Kubernetes!

Reference
https://kubernetes.io/docs/concepts/services-networking/service/#publishing-services-service-types

Kubernetes 系列一 Access Applications in a Cluster by Publishing Services

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