# Dynamic Resource Rebalancing (DRR)

In this document you will learn about <code class="expression">space.vars.product\_name</code> Dynamic Resource Rebalancing (DRR), an automated feature that optimizes resource utilization of your virtualized clusters. DRR ensures efficient resource utilization via live migration of virtual machines, preventing performance bottlenecks.

## Introduction

In any dynamic virtualized environment, workloads fluctuate. Some virtual machines might become resource-intensive, while others remain idle. This can lead to imbalances across the physical hypervisor hosts within a cluster – some hosts become overloaded, causing performance degradation for their VMs, while other hosts sit underutilized. <code class="expression">space.vars.product\_name</code> addresses this challenge with its integrated **Dynamic Resource Rebalancing (DRR)** feature. DRR works continuously to ensure that resources like CPU and memory are utilized efficiently and that no single host becomes a performance bottleneck.

## How DRR works: Continuous Optimization

DRR functions as an ongoing optimization engine for your cluster:

1. **Continuous Monitoring:** DRR constantly monitors key resource utilization metrics, such as CPU and memory usage, across all active hosts within the cluster. It leverages real-time and historical data (gathered via Prometheus) to understand workload patterns.
2. **Imbalance Detection:** The system analyzes the collected metrics to identify significant imbalances in resource consumption. It pinpoints hosts that are becoming overloaded (“hotspots”) and those that have spare capacity.
3. **Automated Live Migration:** When DRR determines that rebalancing would improve the overall health and performance of the cluster, it automatically initiates **Live Migration** (Platform9’s equivalent of VMware vMotion). It intelligently selects appropriate VMs and moves them seamlessly to less-utilized hosts *without downtime* for the VM or its applications. The goal is proactive balancing to prevent resource contention before it impacts VM performance.
4. **Intelligent Placement:** Beyond just rebalancing running VMs, DRR’s logic also contributes to making smarter initial placement decisions when new VMs are powered on, assigning them to the most suitable host based on current cluster load and VM requirements.

## Configuration and control

Platform9 aims for simplicity with DRR:

* **Cluster-Level Setting:** DRR is a feature configured at the cluster level within <code class="expression">space.vars.product\_name</code> .
* **Enabled by Default:** It is typically enabled by default when you create a new cluster, ensuring that workload balancing begins automatically. You generally have the option to disable it per cluster if needed for specific use cases.
* **Automated Operation:** Unlike VMware DRS which offers multiple automation levels and thresholds, Platform9 DRR primarily functions as a continuous, automated optimization engine based on its internal logic.

## Benefits of using Platform9 DRR

Enabling DRR in your <code class="expression">space.vars.product\_name</code> environment delivers tangible benefits:

* **Consistent VM Performance:** Helps prevent performance issues caused by resource contention on overloaded hosts.
* **Optimized Resource Utilization:** Ensures that your hardware investment is used more efficiently across the cluster.
* **Proactive Problem Avoidance:** Identifies and resolves potential resource bottlenecks before they negatively impact applications.
* **Reduced Operational Overhead:** Automates the complex task of monitoring and balancing VM workloads, freeing up administrator time.


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