---
title: "Comparison of Cluster Autoscaler and KEDA MachineSet Autoscaling on Red Hat OpenShift"
description: "This article compares two autoscaling approaches for Red Hat OpenShift compute infrastructure: the built-in Cluster Autoscaler and the KEDA-driven MachineSet Autoscaler. The key difference is the trigger mechanism: Cluster Autoscaler reacts to Pending pods, while KEDA scales based on external metrics like PromQL queries. KEDA triggers faster, scaling within about 15 minutes versus 24 minutes for Cluster Autoscaler, because it acts on metric thresholds before pods become unschedulable. Cluster Autoscaler offers built-in scale-down safety and zero configuration, while KEDA provides fine-grained, metric-driven control but requires the Custom Metrics Autoscaler operator. The choice depends on workload predictability, with Cluster Autoscaler suited for general-purpose workloads and KEDA for dedicated pools with predictable metric patterns. The two autoscalers cannot coexist on the same MachineSet, as they would fight over replica counts."
---

# Comparison of Cluster Autoscaler and KEDA MachineSet Autoscaling on Red Hat OpenShift

[Red Hat](https://yomu.fyi/company/red-hat) · Ramon Gordillo Gutierrez, Jose Ortiz Padilla · Sep 21, 2026

**Type:** Explainer

## Summary

This article compares two autoscaling approaches for Red Hat OpenShift compute infrastructure: the built-in Cluster Autoscaler and the KEDA-driven MachineSet Autoscaler. The key difference is the trigger mechanism: Cluster Autoscaler reacts to Pending pods, while KEDA scales based on external metrics like PromQL queries. KEDA triggers faster, scaling within about 15 minutes versus 24 minutes for Cluster Autoscaler, because it acts on metric thresholds before pods become unschedulable. Cluster Autoscaler offers built-in scale-down safety and zero configuration, while KEDA provides fine-grained, metric-driven control but requires the Custom Metrics Autoscaler operator. The choice depends on workload predictability, with Cluster Autoscaler suited for general-purpose workloads and KEDA for dedicated pools with predictable metric patterns. The two autoscalers cannot coexist on the same MachineSet, as they would fight over replica counts.

## Context

The article compares two autoscaling solutions for Red Hat OpenShift: the built-in Cluster Autoscaler and the KEDA-driven MachineSet Autoscaler. It details their trigger mechanisms, scaling behavior, and operational differences, including a comparison table and guidance on when to use each.

## Takeaways

- Cluster Autoscaler reacts to Pending pods and scales up in one shot, while KEDA scales based on metric thresholds and adds nodes step-by-step, triggering earlier.
- KEDA scales faster (about 15 minutes total) than Cluster Autoscaler (about 24 minutes) because it acts on metrics before pods become unschedulable, though both have similar VM provisioning times.
- The two autoscalers cannot target the same MachineSet simultaneously, as they would conflict over replica counts; they must be used on separate MachineSets.

## FAQ

### Can Cluster Autoscaler and KEDA autoscalers coexist?

Yes, but not on the same MachineSet. They can be used on separate MachineSets, such as one for general workloads and another for dedicated, metrics-driven scaling. If both target the same MachineSet, they will fight over replica counts and cause flapping.

### What is the main difference in scaling triggers?

Cluster Autoscaler is reactive, scaling when pods are Pending due to insufficient resources. KEDA is proactive, scaling based on metric thresholds like CPU utilization or queue depth, allowing it to add capacity before pods become unschedulable.

### Which autoscaler is faster at scaling up?

KEDA is faster, taking about 15 minutes total to reach 3 nodes, compared to about 24 minutes for Cluster Autoscaler. This is because KEDA triggers earlier on metric thresholds, while Cluster Autoscaler waits for the scheduler to mark pods as unschedulable.

**Tags:** [Autoscaling](https://yomu.fyi/topic/autoscaling), [Cluster Autoscaler](https://yomu.fyi/topic/cluster-autoscaler), [KEDA](https://yomu.fyi/topic/keda), [Kubernetes](https://yomu.fyi/topic/kubernetes), [OpenShift](https://yomu.fyi/topic/openshift)

- Source: [Red Hat](https://developers.redhat.com/articles/2026/09/21/comparison-of-cluster-autoscaler-and-keda-machineset-autoscaling-on-red-hat-openshift)
- Source URL: https://developers.redhat.com/articles/2026/09/21/comparison-of-cluster-autoscaler-and-keda-machineset-autoscaling-on-red-hat-openshift
- Ingested by Yomu: 2026-09-21T15:00:17.651Z

[Read original post](https://developers.redhat.com/articles/2026/09/21/comparison-of-cluster-autoscaler-and-keda-machineset-autoscaling-on-red-hat-openshift)