Step 1 of 8 - Virtualization
You're running an estate, not a cluster
Every cluster below was sized for its own peak, so every one of them idles.
Deployment model
75 nodes running 90 vCPU of actual work.
The arithmetic, in full
| Step | Working | Result |
|---|---|---|
| Provisioned today | 25 clusters of 3 nodes each, 75 in total x 8 vCPU | 600 vCPU |
| Mean demand | 600 vCPU x 15.0% estate average utilization (per-cluster 5.4% to 24.3%, sd 4.6%) | 90 vCPU |
| Aggregate peak | 90.0 vCPU x (1 + (2.23 - 1) / sqrt(25)), a pooled peak-to-mean of 1.246 | 112 vCPU |
| Consolidated, sized once for the peak | max(3, ceil(112.1 vCPU / (8 vCPU x 37.5% target))) = max(3, ceil(37.37)); the mean sits well under that peak | 38 nodes, averaging 29.6% |
| Auto-scaled through the day | the pool follows the pooled curve in whole nodes, 30 minutes behind it, holding its size for 2 hours before shrinking | 31 nodes on average, at 36.3% CPU |
| Utilization across the day | 29.5% to 39.2% against a 37.5% setpoint: the pool runs hot while it's a bucket behind a rise, and cool while the cooldown is still holding capacity after a peak | 29.5%-39.2% |
Assumptions
- 8 vCPU per node. Standalone clusters are drawn around 3 nodes, snapped to an odd number for quorum and held between 3 and 15; in this estate they're all 3, because a spread centred on the end of that range has nowhere to go, for 75 nodes in total.
- Each standalone cluster's CPU is a draw from a normal distribution centred on 15.0% and held between 0% and 100%; in this estate they run 5.4% to 24.3%, a 4.6-point standard deviation. The published band is 10-15% today against a 30-45% auto-scaled target, and this Private Host Cluster is set to 37.5%.
- The Private Host Cluster floors at 3 nodes and must reach 38 at peak.
- The auto-scaler sizes for what it saw 30 minutes ago and waits 2 hours before shrinking, so the pool averages 36.3% rather than sitting on its 37.5% setpoint.
- Workloads are independent; consolidation moves where work runs, not how much there is.
What a virtual cluster gives an app team
Its own connection string, databases, schemas, users, roles and backups, and no visibility into the Private Host Cluster or any other virtual cluster.