Kubernetes HTTP Probe Failed with Status Code 404: Causes, Troubleshooting & Best Practices

In Kubernetes environments, an HTTP probe failure with status code 404 indicates that the specified endpoint is not found. This issue is significant because it can prevent the pod from being marked as healthy, leading to potential downtime and disrupted services. Properly configuring and troubleshooting these probes is crucial for maintaining application reliability and availability.

Understanding HTTP Probes in Kubernetes

HTTP probes in Kubernetes are used to check the health of a container. They play a crucial role in ensuring that your application is running smoothly by periodically sending HTTP requests to a specified endpoint within the container.

Role of HTTP Probes

Liveness Probes: These determine if a container is running. If the probe fails, Kubernetes will restart the container.
Readiness Probes: These check if a container is ready to handle traffic. If the probe fails, the container is temporarily removed from the service load balancers.

How They Work

Configuration: You define an HTTP probe in your pod’s YAML configuration. You specify the endpoint, the HTTP method, and the expected response status codes (usually 200-399 for success).
Execution: Kubernetes sends HTTP requests to the specified endpoint at regular intervals. If the response status code is within the expected range, the probe is considered successful.

HTTP Probe Failed with Status Code 404

When you encounter a kubernetes http probe failed with statuscode 404 error, it means the specified endpoint is not found. This can happen due to:

Incorrect endpoint path in the probe configuration.
The application inside the container not serving the expected endpoint.
Delays in the application startup, causing the probe to fail before the endpoint is ready.

To resolve this, ensure the endpoint path is correct and the application is properly configured to serve it. You might also need to adjust the probe’s initial delay to give the application more time to start.

Common Causes of HTTP Probe Failures

Here are common reasons why a Kubernetes HTTP probe might fail with status code 404:

Misconfigurations:

Incorrect URL Path: The specified path in the probe configuration does not exist on the application server.
Wrong Port: The probe is configured to check a port that the application is not listening on.
Host Header Issues: The probe might need a specific Host header to reach the correct service, which is not configured.
Scheme Mismatch: The probe is set to use HTTP instead of HTTPS or vice versa.

Application Issues:

Application Not Ready: The application has not fully started or is not ready to serve requests when the probe is executed.
Service Not Exposed: The application service is not properly exposed or is down.
Permissions: The container does not have the necessary permissions to access the specified URL.
Server Down: The server hosting the application is down or unreachable.

Troubleshooting Steps

Sure, here’s a step-by-step guide to troubleshoot the “Kubernetes HTTP probe failed with statuscode 404” error:

Check Pod Status:
```
kubectl get pods
```
Ensure the pod is running and not in a crash loop.
Describe the Pod:
```
kubectl describe pod <pod-name>
```
Look for events related to the probe failure.
Check Probe Configuration:
- Verify the path in the probe configuration.
- Ensure the port is correct and the service is listening on that port.
- Example configuration:
```
livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 3
  periodSeconds: 3
```
Check Application Logs:
```
kubectl logs <pod-name>
```
Look for any errors or issues in the application logs that might indicate why the endpoint is returning a 404.
Verify Endpoint Availability:
- Use curl or a similar tool to check the endpoint from within the pod:
```
kubectl exec -it <pod-name> -- curl -v http://localhost:8080/healthz
```
- Ensure the endpoint is accessible and returning the expected response.

Check Service Configuration:

Ensure the service is correctly configured to route traffic to the pod.

Example service configuration:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080

Increase Initial Delay:

If the application takes time to start, increase the initialDelaySeconds in the probe configuration.

Example:

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 10
  periodSeconds: 5

Check Network Policies:
- Ensure there are no network policies blocking the traffic to the pod.
Review Deployment Configuration:
- Ensure the deployment configuration is correct and matches the expected setup.
Restart Pod:
```
kubectl delete pod <pod-name>
```
Allow Kubernetes to recreate the pod and see if the issue persists.

Following these steps should help you identify and resolve the issue with the HTTP probe failing with status code 404.

Best Practices to Avoid HTTP Probe Failures

Here are some best practices for configuring HTTP probes in Kubernetes to prevent 404 errors:

Correct Endpoint: Ensure the probe targets a valid and specific endpoint that accurately reflects the application’s health.
Proper HTTP Method: Use the appropriate HTTP method (GET, POST, etc.) for the probe.
Timeouts and Intervals: Set reasonable timeouts and intervals to avoid premature failures.
Startup Probes: Use startup probes for applications with longer initialization times.
Readiness Probes: Configure readiness probes to check dependencies (e.g., databases, caches) before marking the container as ready.
Liveness Probes: Use liveness probes sparingly to avoid unnecessary restarts.
Custom Scripts: If necessary, use custom scripts to perform more complex health checks.
Avoid Aggressive Checks: Avoid overly aggressive checks that might cause false positives.

These practices can help ensure your probes are effective and reduce the likelihood of encountering 404 errors.

To Troubleshoot a Kubernetes HTTP Probe Failing with Status Code 404

Follow these steps:

Check the pod’s logs for any errors or exceptions that might indicate why the probe is failing.
Verify that the endpoint being targeted by the probe exists and returns a valid response.
Ensure the service configuration is correct and routes traffic to the pod.
Increase the initial delay in the probe configuration if the application takes time to start.
Check network policies to ensure they are not blocking traffic to the pod.
Review deployment configuration to ensure it matches the expected setup.
Restart the pod to see if the issue persists.

Proper Probe Configuration

Is Crucial to Avoid 404 Errors. Best Practices Include:

Using Correct Endpoints
Proper HTTP Methods
Reasonable Timeouts and Intervals
Startup Probes for Applications with Longer Initialization Times
Readiness Probes to Check Dependencies
Liveness Probes Sparingly
Custom Scripts When Necessary
Avoiding Overly Aggressive Checks

By Following These Guidelines, You Can Ensure Your Probes Are Effective and Reduce the Likelihood of Encountering 404 Errors.

Sep 15, 2024
Roderick Webb
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