Capacity Planning Calculator

You are a performance engineer specializing in capacity planning. Help me plan capacity for my system.

System: [SYSTEM_DESCRIPTION]
Current traffic: [CURRENT_TRAFFIC]
Growth forecast: [GROWTH_FORECAST]
Peak patterns: [PEAK_PATTERNS] (daily, weekly, seasonal, event-driven)
Current infrastructure: [INFRASTRUCTURE]
Performance SLAs: [PERFORMANCE_SLAS]
Planned launches/events: [UPCOMING_EVENTS]

Create a capacity plan:

**1. Load Modeling**
- Current baseline: Requests/sec, concurrent users, data throughput
- Peak-to-average ratio
- Growth projection (3, 6, 12 months)
- Headroom requirement (typically 30-50% above peak)

**2. Back-of-Envelope Calculations**

*Storage:*
- Data per user/transaction × expected volume × retention period
- Growth rate of storage needs
- Storage cost projection

*Compute:*
- Requests per second → CPU/memory requirements per instance
- Concurrent connections → connection pool sizing
- Background job throughput requirements

*Network:*
- Bandwidth: Average response size × requests/sec
- Connection limits
- CDN offload potential

*Database:*
- Read QPS and write QPS
- Connection pool sizing
- IOPS requirements
- Storage growth

**3. Scaling Thresholds**
| Resource | Current | Threshold | Scale Action | Time to Scale |
| CPU | ...% | 70% | Add instance | ~3 min (ASG) |
| Memory | ... | 80% | Add instance | ... |
| DB connections | ... | 80% | Increase pool/read replica | ... |
| Disk | ... | 75% | Expand volume | ... |

**4. Scaling Strategy**
- Horizontal vs. vertical for each component
- Auto-scaling configuration (min, max, target, cooldown)
- Pre-scaling for predictable events (marketing launch, Black Friday)
- Database scaling plan (when to add replicas, when to shard)

**5. Load Testing Plan**
- Baseline test: Confirm current capacity
- Stress test: Find breaking points
- Soak test: Verify stability under sustained load
- Spike test: Validate auto-scaling behavior
- Tool recommendation (k6, Gatling, Locust)

**6. Cost Projection**
| Month | Traffic | Infrastructure | Monthly Cost |
- 3, 6, 12 month projections
- Cost per unit metrics (cost per user, per request, per GB)

**7. Risk Scenarios**
- What happens at 2x traffic? 5x? 10x?
- Single points of failure under load
- Degradation plan: What to shed first when overloaded