Kubernetes: Port,Targetport and NodePort

by Anish

Posted on Tuesday August 15, 2018

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Multiple Port Services

1. Many Services need to expose more than one port. Kubernetes supports multiple port definitions on a Service object. When using multiple ports you must give all of your ports names, so that endpoints can be disambiguated. For example, this definition is used in nginx secure deployment in my previous article

   apiVersion: v1
   kind: Service
   metadata:
     name: nginxsvc
     labels:
       app: nginx
   spec:
     type: NodePort
     ports:
     - port: 80
       protocol: TCP
       name: http
     - port: 443
       protocol: TCP
       name: https
     selector:
       app: nginx
   

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   • Port: Port is the port number which makes a service visible to other services running within the same K8s cluster.
   • Target Port: Target port is the port on the POD where the service is running.Service can map an incoming port to any targetPort. By default the targetPort will be set to the same value as the port field
   • Nodeport: Node port is the port on which the service can be accessed from external world using through Kube-Proxy.In NodePort, the Kubernetes master will allocate a port from a range specified by --service-node-port-range flag (default: 30000-32767) , and each Node will proxy that port (the same port number on every Node) into your Service

2. These are IPtables rules in which will be setup by kubernetes in the master-node.

    iptables -t nat --line-numbers -n -L | grep 30287
    1  KUBE-MARK-MASQ  tcp  --  0.0.0.0/0  0.0.0.0/0  /* default/nginxsvc:https */ tcp dpt:**30287**
    2  KUBE-SVC-ER5WGNLE726ZPUG2  tcp  --  0.0.0.0/0  0.0.0.0/0  /* default/nginxsvc:https */ tcp dpt:**30287**
    
    iptables -L | grep 30287
        REJECT tcp  --  anywhere anywhere /* default/nginxsvc:https has no endpoints */ ADDRTYPE match dst-type LOCAL tcp dpt:**30287** reject-with icmp-port-unreachable

3. once the deployment is created , new iptables rules will ge generated, you can find the node port that Kubernetes is using for http and https traffic using the command kubectl get service nginxsvc -o json

    "spec": {
            "clusterIP": "10.103.250.179",
            "externalTrafficPolicy": "Cluster",
            "ports": [
                {
                    "name": "http",
                    "nodePort": 32210,
                    "port": 80,
                    "protocol": "TCP",
                    "targetPort": 80
                },
                {
                    "name": "https",
                    "nodePort": 30287,
                    "port": 443,
                    "protocol": "TCP",
                    "targetPort": 443
                }
            ],

Further Reading

1. Checkout how to deploy HTTPS Secure Nginx deploymet in kubernetes

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