No More Idle Time: Rightsizing Tools for Efficient Kubernetes Clusters

In the traditional server world, the mantra was: “Better too much RAM than too little.” In Kubernetes, this mindset leads directly to a bloated cloud bill. Since Kubernetes schedules Pods based on their Resource Requests, you pay for the space you reserve—regardless of whether your application actually uses it.

We call this phenomenon “Slack”. On average, enterprise Kubernetes clusters are overprovisioned by 30% to 50%. Rightsizing is the process of closing this gap between reservation and actual usage.

The Estimation Dilemma

Developers face a tough task: they must determine how much CPU and RAM their application needs before it has run under real load.

• If they estimate too low, the app crashes (OOM-Kill) or becomes extremely slow (CPU throttling).
• If they estimate too high, the cluster remains stable, but the company wastes money on unused capacity.

The Saviors: Automated Rightsizing Tools

By 2026, guessing is no longer necessary. There are tools that analyze user behavior and provide precise recommendations.

1. Vertical Pod Autoscaler (VPA)

The VPA is the “autopilot” for resources. It observes a Pod’s real consumption over time and automatically adjusts the requests.

• Advantage: It completely eliminates guesswork.
• Challenge: In the default configuration, a Pod must be restarted to apply resource changes (though in-place update features in newer K8s versions increasingly solve this).

2. Goldilocks: “Just Right”

Goldilocks uses VPA recommendations but does not apply them automatically. Instead, it creates a dashboard that visualizes which apps are set “too large” or “too small.”

• Advantage: Ideal for teams that want to retain full control.
• Goal: Find the “perfect” middle ground—not too much, not too little.

3. Kubecost / OpenCost

These tools not only show you millicores and megabytes but also convert them directly into euros and cents.

• Feature: You receive percentage savings potential per project. A report might say: “Your frontend team could save €400 a month by reducing memory requests by 20%.”

Strategy: Trust is Good, Data is Better

Rightsizing should not be a one-time project but part of the continuous deployment process.

1. Observe: Let tools like Goldilocks collect data for two weeks.
2. Adjust: Use the recommendations to adjust requests in your Helm charts or Kustomize files.
3. Automate: For non-critical workloads (Dev/Staging), enable VPA in Auto mode to keep the environment lean permanently.

Conclusion: Efficiency is a Team Sport

Rightsizing tools take away the fear of miscalculation from developers. They allow IT management to reduce costs without compromising stability. Those who do not optimize their cluster resources data-driven by 2026 are leaving money on the table.

Technical FAQ: Rightsizing

Should requests and limits always be the same? Not necessarily. For CPU, it is often wise to set requests low (based on average) and limits high (for peak loads). For RAM, however, requests and limits should be close to each other to avoid unpredictable OOM-Kills by the operating system.

Does the VPA slow down my application? No, the VPA only observes metrics. Adjusting the resources is an administrative task. The application runs just as fast after the update with the new configuration—just on more appropriate hardware.

How to handle Java apps (JVM)? Java applications are special in rightsizing as they often reserve a lot of memory (heap) at startup. Here, rightsizing recommendations must be aligned with JVM parameters (-Xmx, -Xms) to avoid conflicts.