How to Handle Node Problems in Kubernetes

Nodes are the fundamental units in a Kubernetes cluster. Each node represents a physical or virtual machine that provides the computational resources, including CPU, memory, and storage, needed to run containers. The Kubernetes control plane manages these nodes and distributes workloads across them to maintain high availability and scalability. Maintaining the health of these nodes is critical for the stability of your applications.

For a deeper understanding of Nodes in Kubernetes, refer to the official documentation: Kubernetes Nodes

Common Node Issues

Memory Pressure
Memory pressure is encountered when a node’s memory is nearly exhausted, leading to potential pod eviction.. You can diagnose this with:

root@rke2-server1:~# kubectl top nodes
NAME               CPU(cores)   CPU%   MEMORY(bytes)   MEMORY%
rke2-agent1        1810m        5%     10608Mi         4%
rke2-agent2        710m         2%     9131Mi          94%
rke2-server1       1346m        4%     14869Mi         11%
root@rke2-server1:~#

Here, rke2-agent2 is close to exhausting its memory, with 94% usage. To mitigate this, consider reducing the number of pods, optimizing resource requests, or scaling up memory resources.

Disk Pressure
Disk pressure is triggered when available disk space is low, leading to pod eviction or performance degradation. Diagnose this by describing the node:

root@rke2-server1:~# kubectl describe node

Example output:

Conditions:
Type              Status
----              ------
DiskPressure      True
MemoryPressure    False

If DiskPressure is True, you might need to clear logs, move data off-node, or add more disk space to fix the issue.

Node Not Ready States
A ‘Not Ready’ state means the node cannot host pods. In particular, this could be due to network issues, kubelet crashes, or resource exhaustion. To check the status:

root@rke2-server1:~# kubectl get nodes
NAME               STATUS   ROLES                       AGE   VERSION
rke2-agent1        Ready    <none>                      70d   v1.27.10+rke2r1
rke2-agent2        NotReady <none>                      70d   v1.27.10+rke2r1
rke2-server1       Ready    control-plane,etcd,master   70d   v1.27.10+rke2r1
root@rke2-server1:~#

Further inspection can be done with:

root@rke2-server1:~# kubectl describe node rke2-agent2
root@rke2-server1:~# kubectl logs <kubelet-pod-name> -n kube-system

Restarting the node, fixing network issues, or addressing kubelet errors often restores the node to a “Ready” state.

Tools & Techniques

• kubectl
  The primary tool for managing Kubernetes nodes is kubectl. It provides commands like kubectl top nodes for resource monitoring and kubectl describe node for detailed status and condition information.
• Prometheus & Grafana
  For advanced monitoring, Prometheus and Grafana are powerful tools. Prometheus collects metrics from your nodes and cluster, while Grafana visualizes these metrics in dashboards, making it easier to identify trends and issues. Setting up alerts in Prometheus can notify you of node problems before they impact your workloads.
• Node Problem Detector
  The health of nodes is monitored by the Node Problem Detector (NPD), a daemon set that reports problems to the Kubernetes control plane. It helps in detecting issues like kernel problems, disk IO errors, and network failures, allowing for more proactive management. For more details on Node Problem Detector refer the official documentation.
• Kubernetes Dashboard
  The Kubernetes Dashboard provides a web-based UI that gives a graphical overview of node health and resource usage. It can be a quick and easy way to monitor node status without diving into the command line.

Maintaining node health in Kubernetes is vital for ensuring that your cluster runs smoothly. By consistently monitoring and resolving issues like memory pressure, disk pressure, and nodes in “Not Ready” states, you can keep your applications running reliably. Moreover, tools such as kubectl, Prometheus, Grafana, and the Kubernetes Dashboard are instrumental in efficiently managing node health and proactively preventing problems.

Furthermore, if the enhancement of your troubleshooting skills in Kubernetes interests you, these related posts can be checked out

1. Troubleshooting Pod Failures in Kubernetes: A Comprehensive Guide
2. Resolving Service Discovery Problems in Kubernetes

Thank you for taking the time to read this guide. Maintaining healthy nodes ensures the long-term success of your Kubernetes deployments. If you have any questions or feedback, feel free to reach out. Happy clustering!