kubernetes service

service type

k8s中service主要有三种：

• ClusterIP: use a cluster-internal IP only - this is the default and is discussed above. Choosing this value means that you want this service to be reachable only from inside of the cluster.
• NodePort: on top of having a cluster-internal IP, expose the service on a port on each node of the cluster (the same port on each node). You’ll be able to contact the service on any :NodePort address.
• LoadBalancer: on top of having a cluster-internal IP and exposing service on a NodePort also, ask the cloud provider for a load balancer which forwards to the Service exposed as a :NodePort for each Node.

clusterIP

clusterIP主要作用是方便pod到pod之间的调用。

[minion@te-yuab6awchg-0-z5nlezoa435h-kube-master-udhqnaxpu5op ~]$ kubectl describe service redis-sentinel Name:           redis-sentinelNamespace:      defaultLabels:         name=sentinel,role=serviceSelector:       redis-sentinel=trueType:           ClusterIPIP:         10.254.142.111Port:           <unnamed>   26379/TCPEndpoints:      <none>Session Affinity:   NoneNo events.

clusterIP主要在每个node节点使用iptables，将发向clusterIP对应端口的数据，转发到kube-proxy中。

[minion@te-yuab6awchg-0-z5nlezoa435h-kube-master-udhqnaxpu5op ~]$ sudo iptables -S -t nat...-A KUBE-PORTALS-CONTAINER -d 10.254.142.111/32 -p tcp -m comment --comment "default/redis-sentinel:" -m tcp --dport 26379 -j REDIRECT --to-ports 36547-A KUBE-PORTALS-HOST -d 10.254.142.111/32 -p tcp -m comment --comment "default/redis-sentinel:" -m tcp --dport 26379 -j DNAT --to-destination 10.0.0.5:36547

然后kube-proxy自己内部实现有负载均衡的方法，并可以查询到这个service下对应pod的地址和端口，进而把数据转发给对应的pod的地址和端口。

nodePort/LoadBalancer

nodePort跟LoadBalancer其实是同一种方式。

区别在于LoadBalancer比nodePort多了一步，就是可以调用cloud provider去创建LB来向节点导流。cloud provider好像支持了openstack、gce等系统。

nodePort的原理在于在node上开了一个端口，将向该端口的流量导入到kube-proxy，然后由kube-proxy进一步导给对应的pod。

所以service采用nodePort的方式，正确的方法是在前面有一个lb，然后lb的后端挂上所有node的对应端口。这样即使node1挂了。lb也可以把流量导给其他node的对应端口。

我们使用这样的一个manifest来创建service

apiVersion: v1kind: Servicemetadata:  labels:    name: ssh    role: service  name: ssh-service1spec:  ports:    - port: 2222      targetPort: 22      nodePort: 30239  type: NodePort  selector:    ssh-service: "true"

使用get service可以看到虽然type是NodePort，但是依然为其分配了一个clusterIP。分配clusterIP的作用还是如上文所说，是方便pod到service的数据访问。

[minion@te-yuab6awchg-0-z5nlezoa435h-kube-master-udhqnaxpu5op ~]$ kubectl get service NAME LABELS SELECTOR IP(S) PORT(S) kubernetes component=apiserver,provider=kubernetes   <none>                10.254.0.1       443/TCPssh-service1     name=ssh,role=service                     ssh-service=true      10.254.132.107   2222/

使用describe可以查看到详细信息。可以看到暴露出来的NodePort端口，正是指定的30239

[minion@te-yuab6awchg-0-z5nlezoa435h-kube-master-udhqnaxpu5op ~]$ kubectl describe service ssh-service1 Name:           ssh-service1Namespace:      defaultLabels:         name=ssh,role=serviceSelector:       ssh-service=trueType:           LoadBalancerIP:         10.254.132.107Port:           <unnamed>   2222/TCPNodePort:       <unnamed>   30239/TCPEndpoints:      <none>Session Affinity:   NoneNo events.

nodePort的工作原理与clusterIP大致相同，是发送到node上指定端口的数据，通过iptables重定向到kube-proxy对应的端口上。然后由kube-proxy进一步把数据发送到其中的一个pod上。

[minion@te-yuab6awchg-0-z5nlezoa435h-kube-master-udhqnaxpu5op ~]$ sudo iptables -S -t nat...-A KUBE-NODEPORT-CONTAINER -p tcp -m comment --comment "default/ssh-service1:" -m tcp --dport 30239 -j REDIRECT --to-ports 36463-A KUBE-NODEPORT-HOST -p tcp -m comment --comment "default/ssh-service1:" -m tcp --dport 30239 -j DNAT --to-destination 10.0.0.5:36463-A KUBE-PORTALS-CONTAINER -d 10.254.0.1/32 -p tcp -m comment --comment "default/kubernetes:" -m tcp --dport 443 -j REDIRECT --to-ports 53940-A KUBE-PORTALS-CONTAINER -d 10.254.132.107/32 -p tcp -m comment --comment "default/ssh-service1:" -m tcp --dport 2222 -j REDIRECT --to-ports 36463-A KUBE-PORTALS-HOST -d 10.254.0.1/32 -p tcp -m comment --comment "default/kubernetes:" -m tcp --dport 443 -j DNAT --to-destination 10.0.0.5:53940-A KUBE-PORTALS-HOST -d 10.254.132.107/32 -p tcp -m comment --comment "default/ssh-service1:" -m tcp --dport 2222 -j DNAT --to-destination 10.0.0.5:36463

原文地址：https://xuxinkun.github.io/2016/03/27/k8s-service/

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作者：jiankunking 出处：http://blog.csdn.net/jiankunking