Kubernetes Control Plane Logs: A Comprehensive Guide

Kubernetes has become the de facto standard for container orchestration in modern cloud - native applications. The control plane of Kubernetes is the brain of the entire cluster, responsible for making global decisions about the cluster, detecting and responding to cluster events. Kubernetes control plane logs are a crucial source of information for monitoring, troubleshooting, and auditing the cluster’s health and operations. In this blog post, we will delve into the core concepts, typical usage examples, common practices, and best practices related to Kubernetes control plane logs.

Table of Contents

  1. Core Concepts
  2. Typical Usage Examples
  3. Common Practices
  4. Best Practices
  5. Conclusion
  6. References

Core Concepts

What are Kubernetes Control Plane Logs?

The Kubernetes control plane consists of several key components, including the API Server, etcd, Controller Manager, and Scheduler. Each of these components generates logs that record their activities, errors, and important events. These logs can provide insights into the internal workings of the control plane, such as API requests, object creation and deletion, and scheduling decisions.

Log Sources

  • API Server: The API Server is the front - end for the Kubernetes control plane. Its logs contain information about incoming API requests, authentication and authorization events, and resource validation. For example, if a user tries to create a pod with an invalid configuration, the API Server log will record the validation error.
  • etcd: etcd is a distributed key - value store that stores the cluster’s state. Its logs record operations like key - value updates, leader elections, and network connectivity issues.
  • Controller Manager: The Controller Manager runs controllers that regulate the state of the cluster. Logs from the Controller Manager show the progress of tasks such as pod creation, scaling, and garbage collection.
  • Scheduler: The Scheduler is responsible for assigning pods to nodes. Its logs contain details about scheduling decisions, including the list of available nodes, pod requirements, and the reason for choosing a particular node.

Log Levels

Kubernetes components support different log levels, which can be configured to control the verbosity of the logs. The most common log levels are:

  • 0: Error - level logging. Only critical errors are logged.
  • 1: Warning - level logging. Errors and warnings are logged.
  • 2 - 4: Info - level logging. General information about the component’s activities is logged.
  • 5+: Debug - level logging. Detailed information for debugging purposes is logged.

Typical Usage Examples

Troubleshooting API Request Errors

Suppose a user reports that they are unable to create a new deployment. By checking the API Server logs, we can look for error messages related to the deployment creation request. For example, if there is a permission issue, the log might show an “Unauthorized” error.

kubectl logs -n kube - system kube - api - server - <pod - name> | grep "Unauthorized"

Monitoring etcd Performance

To monitor the performance of etcd, we can check its logs for slow operations. Slow operations can indicate performance bottlenecks or network issues.

kubectl logs -n kube - system etcd - <pod - name> | grep "slow"

Debugging Scheduler Decisions

If a pod is not being scheduled as expected, we can check the Scheduler logs to understand why. The logs will show the list of nodes considered, the pod’s requirements, and the reason for the scheduling decision.

kubectl logs -n kube - system kube - scheduler - <pod - name> | grep "Scheduling"

Common Practices

Centralized Logging

Centralizing Kubernetes control plane logs is a common practice. Tools like Elasticsearch, Logstash, and Kibana (ELK stack) or Fluentd and Grafana can be used to collect, store, and visualize the logs. This allows operators to easily search and analyze logs from multiple components across the cluster.

Log Retention

It is important to define a log retention policy. Depending on the regulatory requirements and the cluster’s usage, logs can be retained for a few days to several months. Older logs can be archived or deleted to save storage space.

Log Filtering

When dealing with a large volume of logs, filtering the logs based on relevant criteria can save time. For example, we can filter logs by component, log level, or time range.

Best Practices

Use Structured Logging

Kubernetes components support structured logging, which formats logs as JSON objects. Structured logs are easier to parse and analyze programmatically. For example, in a JSON - formatted log, we can easily extract specific fields like the timestamp, log level, and message.

Regularly Review Logs

Regularly reviewing control plane logs can help detect potential issues before they become critical. Set up a schedule to review logs and look for patterns or anomalies.

Secure Logs

Control plane logs may contain sensitive information such as API keys and user credentials. Ensure that logs are stored securely, and access to the logs is restricted to authorized personnel.

Conclusion

Kubernetes control plane logs are a valuable resource for maintaining the health and security of a Kubernetes cluster. By understanding the core concepts, using typical usage examples, following common practices, and implementing best practices, intermediate - to - advanced software engineers can effectively monitor, troubleshoot, and audit their Kubernetes clusters.

References