When working with Kubernetes Service, you will come across some of the following terminologies:
- Port: Port is the port number which makes a service visible to other services running within the same K8s cluster. In other words, in case a service wants to invoke another service running within the same Kubernetes cluster, it will be able to do so using port specified against “port” in the service spec file.
- Target Port: Target port is the port on the POD where the service is running.
- Nodeport: Node port is the port on which the service can be accessed from external users using Kube-Proxy.
Take a look at following spec defining a sample service:
apiVersion: v1
kind: Service
metadata:
name: order-service
spec:
ports:
- port: 8080
targetPort: 8170
nodePort: 32222
protocol: TCP
selector:
component: order-service-app
Pay attention to some of the following in above spec:
- The port is 8080 which represents that order-service can be accessed by other services in the cluster at port 8080.
- The targetPort is 8170 which represents the order-service is actually running on port 8170 on pods
- The nodePort is 32222 which represents that order-service can be accessed via kube-proxy on port 32222.
This is ipTables in Kubernetes which does the magic. It maintains the mapping of nodePort vs targetPort. K8s Kube-Proxy uses the ipTables to resolve the requests coming on a specific nodePort and redirect them to appropriate pods.
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Check out my latest book titled as First Principles Thinking: Building winning products using first principles thinking.
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it should be “When working with Kubernetes SERVICE” and not “When working with Kubernetes Pod”