In Kubernetes (K8S), if there is a problem with Service access, you can usually follow the following steps for detailed troubleshooting:

1. Check the status and configuration of the Service

Operation:

• Use the kubectl describe service <service-name> commandto view the detailed description of the Service and ensure that the Service type (e.g., ClusterIP, NodePort, LoadBalancer, etc.) and port mapping (e.g., port, targetPort, nodePort, etc.) are configured correctly.
• Verify that the Service's selector (selector) correctly matches the desired Pod.

Purpose:

• Ensure that the Service is configured correctly to correctly identify and associate with the target Pod.

2. Check the status of the Pod to which the Service points.

Operation:

• Use kubectl get podsto check the status of all Pods and ensure that the associated Pod is in the Running state (Running).
• If the Pod is not running, use kubectl describe pod <pod-name> to viewthe details of the Pod, find out the reason and resolve it.

Purpose:

• Ensure that the Pods on which the Service depends are healthy and able to provide the service normally.

3. check if restrictions are added to the network policy

operation:

• Use kubectl get networkpoliciesto view the current network policy configuration.
• Check if there are network policies restricting access to the Service and adjust the policies accordingly or remove unnecessary restrictions.

Purpose:

• Troubleshoot Service access problems caused by improper network policies.

4. check the network connection between Service and Pod.

Operation:

• Create a temporary Pod inside the cluster and use the kubectl run --rm -it --image alpine ping <service-name> commandto test the connectivity to the Service.
• If you can't ping, it may be a network configuration or firewall issue.
• Use kubectl run --rm -it --image alpine nslookup <service-name> to testif DNS resolution is working.

Purpose:

• Verify the network connectivity between the Service and the Pod and that the DNS resolution is correct.

5. Check kube-proxy and network plugins

Operation:

• Check if the kube-proxy service is running properly. you can use ps auxw | grep kube-proxyto see if the kube-proxy process exists.
• Check the logs of kube-proxy, use kubectl logs <kube-proxy-pod-name> orcheck the kube-proxy related logs in system logs (e.g. /var/log/messages ).
• Check that the network plugins (e.g. Calico, Flannel, etc.) are working properly and make sure that there are no problems with the configuration and status of the network plugins.

Purpose:

• Troubleshoot Service access issues caused by kube-proxy or network plugin failures.

6. check the CoreDNS service

Operation:

• Use kubectl get pods -n kube-systemto check the status of the CoreDNS service.
• If the CoreDNS service is not running, check its logs and try restarting the service.
• Ensure that CoreDNS is properly configured to resolve the Service's DNS records correctly.

Purpose:

• Verify that the cluster's DNS service is working properly to ensure that Service's DNS resolves correctly.

7. view the Service's Endpoints.

operation:

• Use kubectl get endpoints <service-name> to viewthe Endpoints information for the Service.
• Ensure that the Endpoints list contains the correct Pod IP and port.

Purpose:

• Verify that the Service is correctly associated with the Pod and ensure that the Endpoints information is correct.

In summary, it is usually possible to locate and resolve Service access issues in Kubernetes. If the problem persists, it may be necessary to further check the cluster logs, events or consult professional technical support.