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Learn how to troubleshoot connection issues between a Kubernetes service and its associated pod. This guide explains essential adjustments for successful TCP communication.
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This video is based on the question https://stackoverflow.com/q/65212786/ asked by the user 'Neha' ( https://stackoverflow.com/u/14707563/ ) and on the answer https://stackoverflow.com/a/65213783/ provided by the user 'Shai Katz' ( https://stackoverflow.com/u/1609014/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Verifying Connection to a Kubernetes Pod Using Service Cluster IP

When working with Kubernetes, ensuring that services are correctly set up to connect to their corresponding pods is paramount. Many users face confusion regarding their services not passing traffic to the intended pods, which can lead to application failures or unexpected behaviors. In this guide, we will explore the steps necessary to verify and troubleshoot the connectivity between a Kubernetes service and a pod.

The Problem at Hand

In our scenario, you have created a server pod and a service that points to it. You've successfully established a TCP connection using the server pod's IP address but encountered issues when trying to connect via the service's Cluster IP. This raises the question: Is the service correctly configured to connect to the server pod?

Analyzing the Configuration

Pod Definition

You defined your server pod with the following specifications:

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Here, your server listens on container port 80, yet the server code is configured to listen on port 8080.

Service Definition

You also created a service to expose this pod:

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This service configuration also defines port 80, which does not match the listening port of the server pod.

The Solution

Step 1: Modify the Service Port

Since the server is listening on port 8080, you need to update your service YAML to route traffic to this port instead of port 80. Here’s how you can adjust the service configuration:

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Step 2: Deploy the Updated Service

Once you’ve made this change, apply the new configuration:

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Step 3: Testing the Connectivity

You can then test the connection again from your client pod using the following steps:

Exec into the Client Pod:

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Finally, attempt to establish a TCP connection to the service using the cluster IP (make sure the service is running):

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If configured correctly, your client should now successfully establish a connection to the server pod via the service.

Conclusion

By ensuring that your service ports align with the port on which your pod is listening, you should be able to resolve connectivity issues in Kubernetes. These adjustments not only help in establishing connections successfully but also reinforce best practices in defining services and managing configurations. If you still face issues after implementing these changes, consider checking network policies or logs for additional information regarding connection attempts.

Keep these guidelines in mind as you work with Kubernetes services, and you'll be well-equipped to handle similar configurations and troubleshooting in the future.