Rancher Node Disk Pressure

What is Rancher Node Disk Pressure

Understanding Rancher

Rancher is an open-source platform designed to manage Kubernetes clusters. It provides a comprehensive suite of tools to deploy, manage, and scale containerized applications across multiple clusters. Rancher simplifies Kubernetes cluster management by offering a user-friendly interface and robust features for monitoring, security, and application deployment.

Identifying the Symptom: Node Disk Pressure

When managing Kubernetes clusters with Rancher, you may encounter the issue of Node Disk Pressure. This symptom is typically observed when a node in your cluster experiences insufficient disk space, leading to potential disruptions in application performance and stability.

What You Might Observe

Common signs of Node Disk Pressure include:

Pods being evicted or failing to start. Warnings or errors in the node status indicating disk pressure. Degraded performance of applications running on the affected node.

Delving into the Issue: Insufficient Disk Space

The root cause of Node Disk Pressure is often insufficient disk space on the node. Kubernetes monitors node resources and applies pressure when disk space is low, which can lead to pod eviction to free up resources. This is crucial for maintaining cluster health but can disrupt workloads.

Understanding Disk Pressure

Disk pressure occurs when the available disk space falls below a certain threshold. Kubernetes uses this metric to decide when to evict pods to prevent the node from running out of space completely. For more details on how Kubernetes handles disk pressure, refer to the Kubernetes documentation on node pressure eviction.

Steps to Resolve Node Disk Pressure

To address Node Disk Pressure, you need to either free up disk space or add additional storage to the affected node. Here are the steps you can take:

Freeing Up Disk Space

Identify large or unnecessary files on the node using commands like du and find:

du -sh /* | sort -h

Remove unnecessary files or logs that are consuming disk space:

rm -rf /path/to/unnecessary/files

Consider cleaning up unused Docker images and containers:

docker system prune -a

Adding Additional Storage

Attach additional storage to the node. This can be done through your cloud provider's console or by physically adding more storage to the server. Ensure the new storage is mounted and available for use. Update the node's configuration to recognize the additional space. Verify that the node no longer reports disk pressure by checking the node status:

kubectl describe node <node-name>

Conclusion

By understanding and addressing Node Disk Pressure, you can ensure the smooth operation of your Kubernetes clusters managed by Rancher. Regular monitoring and maintenance of node resources are essential to prevent such issues from affecting your applications. For more information on managing Kubernetes resources, visit the Rancher documentation.