Kubernetes(6) Service

标签：ali   kubectl   ant   nali   objects   root   metadata   template   dom   

1 Service

Kubernetes Pods are mortal. They are born and when they die, they are not resurrected. ReplicaSets in particular create and destroy Pods dynamically (e.g. when scaling out or in). While each Pod gets its own IP address, even those IP addresses cannot be relied upon to be stable over time. This leads to a problem: if some set of Pods (let’s call them backends) provides functionality to other Pods (let’s call them frontends) inside the Kubernetes cluster, how do those frontends find out and keep track of which backends are in that set?

Enter Services.

A Kubernetes Service is an abstraction which defines a logical set of Pods and a policy by which to access them - sometimes called a micro-service. The set of Pods targeted by a Service is (usually) determined by a Label Selector (see below for why you might want a Service without a selector).

As an example, consider an image-processing backend which is running with 3 replicas. Those replicas are fungible - frontends do not care which backend they use. While the actual Pods that compose the backend set may change, the frontend clients should not need to be aware of that or keep track of the list of backends themselves. The Service abstraction enables this decoupling.

For Kubernetes-native applications, Kubernetes offers a simple Endpoints API that is updated whenever the set of Pods in a Service changes. For non-native applications, Kubernetes offers a virtual-IP-based bridge to Services which redirects to the backend Pods.

PS: there are three working mode for Service -> userspace, iptables and ipvs

• userspace: used for kubernetes 1.1 -
• iptables: between 1.1 and 1.10 -
• ipvs: 1.11+ (current)

Service Type:

ExternalName, ClusterIP, NodePort, and LoadBalancer

2. Create a Service for Redis

using template below:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: redis
      role: logstore
  template:
    metadata:
      labels:
        app: redis
        role: logstore
    spec:
      containers:
        - name: redis
          image: redis:4.0-alpine
          ports:
            - containerPort: 6379
---
apiVersion: v1
kind: Service
metadata:
  name: redis-svc
  namespace: default
spec:
  selector:
    app: redis
    role: logstore
  clusterIP: 10.97.97.97
  type: ClusterIP
  ports:
    - port: 6379
      targetPort: 6379

* port -> service ip address port

* targetPort -> container port

* nodePort -> node port for external communications

Perform command:

[root@k8smaster service]# kubectl apply -f redis-svc.yaml 
service/redis created


[root@k8smaster service]# kubectl get pods -o wide --show-labels
NAME                     READY   STATUS    RESTARTS   AGE   IP            NODE       LABELS
redis-797f4cc7c4-xmvcm   1/1     Running   0          18d   10.244.1.47   k8snode1   app=redis,pod-template-hash=3539077370,role=logstore


[root@k8smaster service]# kubectl get svc -o wide --show-labels
NAME         TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)    AGE   SELECTOR                  LABELS
kubernetes   ClusterIP   10.96.0.1     <none>        443/TCP    24d   <none>                    component=apiserver,provider=kubernetes
redis-svc    ClusterIP   10.97.97.97   <none>        6379/TCP   18d   app=redis,role=logstore   <none>


[root@k8smaster service]# kubectl describe svc redis-svc
Name:              redis-svc
Namespace:         default
Labels:            <none>
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"redis-svc","namespace":"default"},"spec":{"clusterIP":"10.97.97.9...
Selector:          app=redis,role=logstore
Type:              ClusterIP
IP:                10.97.97.97
Port:              <unset>  6379/TCP
TargetPort:        6379/TCP
Endpoints:         10.244.1.47:6379
Session Affinity:  None
Events:            <none>

From the information we can see Endpoints point to 10.244.1.47:6379 which is the random assigned ip and predefined exposed port of redis pod

Endpoints is a kubernetes object. You can also create it manually, this is like a brige between Service and Pod

Kubernetes(6) Service

标签：ali   kubectl   ant   nali   objects   root   metadata   template   dom   

原文地址：https://www.cnblogs.com/crazy-chinese/p/10325519.html