Troubleshooting "HTTP probe failed with statuscode: 500" Errors in GKE with Metrics-Server
Problem: You're experiencing "HTTP probe failed with statuscode: 500" errors in your Google Kubernetes Engine (GKE) cluster when using the Metrics-Server. This usually means the Metrics-Server pod is unhealthy and unable to provide metrics to your cluster.
Rephrased: Imagine your GKE cluster as a bustling city. The Metrics-Server is like the traffic control center, gathering information about how well everything is running. But if the traffic control center is down, the city starts to experience chaos. This error message means your Metrics-Server isn't working correctly, and your cluster can't monitor its performance.
Scenario: Let's say you're running a simple Nginx deployment on your GKE cluster and you've configured the Metrics-Server. You notice that your Nginx pods are occasionally restarting, and you're getting the "HTTP probe failed with statuscode: 500" error message in your logs.
Original Code:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.14.2
ports:
- containerPort: 80
livenessProbe:
httpGet:
path: /
port: 80
initialDelaySeconds: 15
periodSeconds: 20
failureThreshold: 3
Analysis:
This error often arises from the Metrics-Server pod being unable to access the resources it needs, or experiencing internal issues. Here's a breakdown of common causes:
- Resource Constraints: The Metrics-Server might be struggling with limited resources like CPU or memory.
- Network Connectivity: The Metrics-Server might be unable to connect to other components within the cluster, including your Nginx pods.
- Internal Errors: The Metrics-Server itself could be experiencing internal bugs or failures, preventing it from functioning correctly.
- Configuration Issues: Incorrect configuration of the Metrics-Server or its dependencies could lead to this error.
- Dependency Issues: There might be compatibility issues with other components like the kubelet, Kube-state-metrics, or the Kubernetes version.
Troubleshooting Steps:
- Check Logs: Examine the Metrics-Server logs for more detailed information about the error. You can access these logs via the
kubectlcommand:kubectl logs -n kube-system metrics-server-(replacemetrics-server-with the actual pod name). - Check Resource Usage: Use
kubectl top pods -n kube-system metrics-server-to monitor the Metrics-Server's CPU and memory consumption. If the Metrics-Server is experiencing resource constraints, you can adjust its resource requests and limits in the deployment configuration. - Verify Network Connectivity: Check the Metrics-Server's network connectivity by testing its ability to reach other pods within the cluster. You can use the
kubectl execcommand with a pod from the Metrics-Server namespace to test connectivity to other pods. - Inspect Configuration: Review the configuration of your Metrics-Server and ensure it aligns with the documentation and best practices. Double-check the pod definition, the cluster setup, and any other relevant configuration files.
- Update Components: Ensure you're running the latest versions of the Metrics-Server, kubelet, Kube-state-metrics, and Kubernetes. Outdated versions can sometimes lead to compatibility issues.
- Check for External Dependencies: If the Metrics-Server relies on any external services or dependencies, verify their availability and proper functioning.
- Debug with
kubectl describe: Utilize thekubectl describecommand to get detailed information about the Metrics-Server pod, its health, events, and resource allocation.
Example:
Let's say you discover that the Metrics-Server is experiencing high CPU utilization. After reviewing the logs, you notice that the kubelet is struggling to communicate with the Metrics-Server, causing performance issues. This indicates a network connectivity problem.
Resolution:
You can resolve this by adding a hostNetwork: true configuration to the Metrics-Server pod definition, allowing it to access network resources directly.
Conclusion:
The "HTTP probe failed with statuscode: 500" error in GKE with Metrics-Server can be challenging to troubleshoot. Understanding the potential causes and following a systematic debugging approach can help you pinpoint the issue and resolve it effectively. By carefully examining logs, resource usage, network connectivity, and configurations, you can identify the root cause and ensure a healthy and efficient Kubernetes environment.
Additional Resources:
