# Use single Cluster Autoscaler across AZs
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Run one Cluster Autoscaler deployment that manages node groups across all Availability Zones — this gives the autoscaler full visibility into cluster-wide capacity and prevents AZ-isolated scaling decisions that lead to imbalanced, over-provisioned clusters.

For the deployment manifest, see the [single-ca-multi-az.yaml](https://github.com/aws-samples/sample-eks-cost-optimization-guide/blob/main/04-karpenter-cost-optimization/single-ca-multi-az.yaml) and [verify-ca-az-distribution.sh](https://github.com/aws-samples/sample-eks-cost-optimization-guide/blob/main/04-karpenter-cost-optimization/verify-ca-az-distribution.sh) to verify node distribution across AZs.

## Actions
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Consolidate multiple per-AZ Cluster Autoscaler deployments into a single instance with `--balance-similar-node-groups=true`. This prevents one AZ from scaling up while another has idle capacity, eliminating cross-AZ over-provisioning.

### Cost impact
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| 
| 
| Configuration | Min Nodes | Monthly Min Cost (m6g.large) | 
| --- |--- |--- |
| 3 CAs × 1 min node | 3 | \~$210/month | 
| 1 CA × 1 min node | 1 | \~$70/month | 
| **Savings** | **2 nodes** | **\~$140/month per cluster** | 

**Key takeaway: **Multiple autoscaler instances per AZ can't see each other's capacity. A single CA with cross-AZ visibility makes globally optimal scaling decisions and avoids redundant nodes sitting idle in one zone while another scales up.