100 Days of DevOps: Day 64

Fix Python App Deployed on Kubernetes Cluster

This article details the successful troubleshooting and resolution of a misconfiguration issue preventing a Python Flask application from being accessible on a Kubernetes cluster via the required NodePort. The deployment, named python-deployment-nautilus, is now fully operational and accessible as specified.

Overview of the Problem

Initial attempts to access the application failed, and terminal output confirmed the service was not configured correctly.

The specific requirements for the fix were:

1. Deployment Name: python-deployment-nautilus
2. Service Type: NodePort
3. Target Port: The default Flask application port (5000).
4. NodePort: 32345.

Three Critical Issues Identified and Resolved

The resolution required correcting errors across both the Deployment and the associated Service objects.

1. Correcting the Deployment Image (Initial Fix)

The primary reason the application was failing to start was an incorrect image name used in the Deployment manifest.

• Initial Status: The Deployment template was using the wrong image (poroko/flask-app-demo).

• Resolution: I used the kubectl edit command to update the Deployment and specify the correct image: poroko/flask-demo-appimage.
  

  thor@jumphost ~$ kubectl edit deployment python-deployment-nautilus
  

  (Inside the editor, the image was changed from the incorrect value to poroko/flask-demo-appimage)

2. Fixing the Service's Target Port

The Service, named python-service-nautilus, was correctly set to use NodePort: 32345, but was routing internal traffic to the wrong container port.

• Initial Status: The service object confirmed the port mapping issue:
  

  thor@jumphost ~$ kubectl get svc python-service-nautilus
  NAME                       TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)           AGE
  python-service-nautilus    NodePort   10.96.182.199   <none>        8080:32345/TCP    5m27s
  

  The targetPort was implicitly or explicitly set to 8080.

• Resolution: The Service object was edited to explicitly change the targetPort from 8080 to 5000, the standard listening port for a Flask application.
  

  thor@jumphost ~$ kubectl edit service python-service-nautilus
  

  (Inside the editor, the following change was made in the spec.ports section:)
  

    ports:
    - nodePort: 32345
      port: 8080
      protocol: TCP
      targetPort: 5000  # CHANGED FROM 8080 TO 5000
  

3. Validating Service Selector Matching

A check was performed to ensure the Service could locate the Pods. This involved inspecting the labels used by the Deployment and confirming they matched the Service selector.

• Validation Command:
  

  thor@jumphost ~$ kubectl get deployment python-deployment-nautilus -o yaml | grep 'selector:' -A 3
  

• Result: The output confirmed the selector label was app: python_app for the Pods, which successfully matched the selector already present in the Service manifest, ensuring proper traffic routing.

Conclusion of the Task

With the corrections made to the Deployment image and the Service's targetPort, the Kubernetes application is now fully functional and compliant with all project requirements.

The application is successfully deployed as python-deployment-nautilus and is externally accessible via the Service python-service-nautilus on the specified NodePort 32345.