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How to easily debug K8S service, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

In Kubernetes, service is a core concept. Here you'll see how to debug K8S services, which are abstract interfaces (host + port) for workloads made up of multiple Pod.

Before we delve into the debug approach, let's briefly review the network, which is the foundation of Kubernetes services.

Containers in a pod share the same cyberspace and IP.

All pod can communicate with each other through IP.

All Pod can be seen on each node, and vice versa.

Pod can see all the services.

So what does all this mean in practice?

In the figure:

Container B in Pod1 can be directly used as localhost addressing Container A

Container B can directly address Pod2 (kubectl get pod-o wide) through its IP. We know that pod2 is not a reliable communication channel when it fails, and a new pod can appear in its location. But we can't chase changing goals.

Next, Container B can access pod 2 and pod 3 through Service x, which bundles their IP with load balancers; therefore, supporting microservice-based applications on K8S plays a vital role.

Although the examination of the internal network structure of Kubernetes is beyond the scope of this article, I will publish some references later for further study.

For now, I encourage you to spend some time in practice experiencing and understanding the network in Kubernetes. For example, you can start a Kubernetes test pod and try to access other pod, nodes, and services from that pod. The command shown here will pop up a Linux shell within the Pod.

Kubectl run-it networktest-image=alpine bin/ash-restart=Never-rm

Now you are in Kubernetes cyberspace and you are free to experiment with commands such as wegt, ping, nslookup, and so on. For example, test the previously listed network requirements in your Kubernetes cluster, nslookup, ping.

Now let's get back to our topic, troubleshooting Kubernetes Services, which is actually a network structure.

Step1: check if kubectl get svc exists in the service

If the service does not exist, there should be a failure in service creation, so check your service definition.

Step2: test your service

Keep in mind that an internal Kubernetes ClusterIP service is not accessible outside the cluster. Therefore, there are two ways to test it. Method one, you can start a test Pod, enter the pod through SSH, and then try to access your service like this:

Kubectl run-it testpod-image=alpine bin/ash-restart=Never-rm

In this article, we start an alpine Docker image as pod to test the service from within:

# works for http serviceswget: # Confirm there is a DNS entry for the service!nslookup

Alternatively, you can forward it to your local computer and test it locally.

Kubectl port-forward 8000:8080

Now, you can access the service through localhost:8000.

Step3: check whether the service is target-related Pod

The Kubernetes service routes inbound traffic to one of the pod based on the label selector, and the traffic is routed to the destination Pod through its IP. So check to see if the service is bound to those pod.

Kubectl describe service | grep Endpoints

After executing the above command, you should see the IP of all Pod associated with the listed workload. If you don't see it, execute Step4.

Step4: checking Pod tags

Ensure that the selector in the Kubernetes service matches the label of the pod.

Kubectl get pods-show-labelskubectl describe svc

As you can see from the screenshot below, the pod label is on the right. The four pod are marked app=tinywebsite and tier=frontend, and these tags match the service selector of "described" below.

Of the four matching Pod, only three are running, and their IP is listed as the endpoint of the service in the highlighted line. You can also see the same IP in the IP column.

Step5: confirm that the service port matches the pod

Finally, make sure that the code in your pod can listen to the targetPort you specified for the service (for example, the port8001 you saw in the screenshot above)!

This is very simple, in order to let you further understand and study the online world of Kubernetes, you are welcome to read the following article.

Deploy an application in Kubernetes

Debug service

Kubernetes network

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