When nodes in a cluster become over-utilized, pod performance suffers. Avoiding or addressing hot nodes can reduce workload latency and increase throughput.  In this blog, we present two Ray Machine Learning serving experiments that show the performance benefit of Luna’s new Hot Node Mitigation (HNM) feature. With HNM enabled, Luna demonstrated a reduction in latency relative to the hot node runs: 40% in the first experiment and 70% in the second. It also increased throughput: 30% in the first and 40% in the second. We describe how the Luna smart cluster autoscaler with HNM addresses hot node performance issues by triggering the allocation and use of additional cluster resources.

A pod's CPU and memory resource requests express its minimum resource allocations.  The Kubernetes (K8s) scheduler uses these values as constraints for placing the pod on a node, leaving the pod pending when the settings cannot be respected.  Cloud cluster autoscalers look at these values on pending pods to determine the amount of resources to add to a cluster.

A pod configured with both CPU and memory requests, and with limits equal to those requests, is in QoS class guaranteed.  A K8s cluster hosting any non-guaranteed pods runs the risk that some nodes in the cluster could become over-utilized when such pods have CPU or memory usage bursts. Bursting pods running on hot nodes can have performance problems.  A bursting pod’s attempts to use CPU above its CPU resource request can be throttled.  And its attempts to use memory above its memory resource request can cause the pod to be killed.  The K8s scheduler can worsen the situation, by continuing to schedule pods onto hot nodes.

Wondering whether cycling out older Kubernetes nodes periodically is a good idea? In the world of Kubernetes administration, the practice of rotating nodes often takes a backseat, even though it holds considerable advantages. While it's true that node cycling isn't universally applicable, it's worth exploring its merits for your environment. In this article, I will delve into many of the compelling reasons why considering node rotation might be beneficial for your clusters. We'll explore the advantages of node rotation in Kubernetes and how it contributes to resource optimization, fault tolerance, security, and performance improvements.

Why might someone think cycling of Kubernetes nodes is unnecessary? One reason for this could be a misconception about the stability of Kubernetes clusters. In environments where nodes rarely fail or resource usage remains relatively consistent, there might be a tendency to prioritize other tasks over node cycling. Additionally, the perceived complexity of implementing node rotation strategies, particularly in large-scale or production environments, could dissuade teams from actively considering it. Some teams might also be unaware of the potential performance gains and reliability improvements that can result from regular node cycling. However, despite these challenges or misconceptions, it's crucial to recognize that neglecting node rotation can lead to issues such as resource exhaustion, reduced fault tolerance, security vulnerabilities, difficulties upgrading to newer versions, and degraded performance over time. By acknowledging the importance of node cycling and implementing proactive strategies, administrators and DevOps teams can ensure the long-term health, resilience, and efficiency of their Kubernetes infrastructure. So, without delay, let's delve into the specifics.