How to Configure Pods in Kubernetes Cluster (GKE) to Use Node's IP Address for Communication with External VMs

Kubernetes, the open-source platform for automating deployment, scaling, and management of containerized applications, is a powerful tool for data scientists. In this tutorial, we’ll explore how to configure Pods in a Kubernetes Cluster (GKE) to use the Node’s IP address for communication with VMs outside the cluster. This is a common requirement for applications that need to interact with services outside the Kubernetes environment.

By Saturn Cloud | Tuesday, August 08, 2023 | Miscellaneous

How to Configure Pods in Kubernetes Cluster (GKE) to Use Node’s IP Address for Communication with External VMs

Prerequisites

Before we start, ensure you have the following:

A Google Cloud account
A Kubernetes cluster on Google Kubernetes Engine (GKE)
kubectl command-line tool installed and configured
Familiarity with Kubernetes concepts like Pods, Nodes, and Services

Step 1: Understanding the Challenge

By default, Pods in a Kubernetes cluster have their own IP addresses. These are different from the Node’s IP address and are not accessible outside the cluster. This can pose a challenge when your Pods need to communicate with VMs outside the cluster.

Step 2: Using NodePort Service

One solution is to use a NodePort service. This type of service makes a specific port on each Node available to the network outside the cluster. The service routes incoming traffic on the NodePort to your Pods.

Here’s an example of a NodePort service:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: NodePort
  selector:
    app: MyApp
  ports:
      - protocol: TCP
        port: 80
        targetPort: 9376

However, this approach has limitations. It exposes a port across all Nodes in your cluster, which might not be desirable for security reasons. Also, you can only use ports in the 30000-32767 range.

Step 3: Using External IPs

A more flexible solution is to use the external IP of the Node. You can configure your service to use the Node’s external IP, allowing Pods to communicate using the Node’s IP address.

Here’s an example:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: LoadBalancer
  externalTrafficPolicy: Local
  selector:
    app: MyApp
  ports:
      - protocol: TCP
        port: 80
        targetPort: 9376

In this example, the externalTrafficPolicy: Local preserves the client source IP and avoids NAT. This allows Pods to communicate with external VMs using the Node’s IP address.

Step 4: Verifying the Configuration

To verify that your Pods are using the Node’s IP address, you can use the kubectl get nodes -o wide command. This will display the external IP addresses of your Nodes.

Then, use the kubectl describe service my-service command to check the details of your service. The Endpoints field should show the IP addresses and ports of your Pods.

Conclusion

Configuring Pods in a Kubernetes Cluster (GKE) to use the Node’s IP address for communication with external VMs can be achieved using the NodePort service or the external IP of the Node. This allows for more flexible and secure communication between your Kubernetes applications and services outside the cluster.

Remember to always verify your configuration to ensure that your Pods are communicating as expected. With these steps, you can effectively manage your Kubernetes environment and ensure seamless interaction between your Pods and external VMs.

References

Keywords: Kubernetes, GKE, Pods, Node’s IP, VMs, NodePort, External IPs, Data Science, Google Cloud, kubectl, Service, Configuration, Networking

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