Capacity Planner

Infrastructure Capacity Planner Skill

When to activate

• Planning infrastructure ahead of a product launch or traffic spike
• Forecasting cloud costs for the next quarter or fiscal year
• Deciding when to scale a service horizontally or vertically
• Evaluating whether to reserve instances vs. use on-demand pricing
• Preparing an infrastructure budget for a fundraising conversation
• Rightsizing over-provisioned resources to cut cloud spend
• Planning database capacity ahead of data growth

When NOT to use

• Real-time incident scaling decisions — use /incident-response
• Architecture redesign — use /aws-architect, /gcp-architect, or /azure-architect
• SLO definition and error budget — use /slo-architect
• Cost optimisation of existing spend (rightsizing, reserved instances) without a planning context — use a dedicated cost tool

Instructions

Core capacity planning prompt

Build a capacity plan for [SERVICE or SYSTEM] for the next [3 / 6 / 12] months.

Current state:
- Service: [what it does]
- Traffic: [current requests/day or RPS]
- Infrastructure: [current compute — e.g., 3x t3.medium EC2, 2 Kubernetes pods, etc.]
- Database: [type, instance size, current storage used]
- Current monthly cloud cost: [$X]
- Current utilisation: [CPU: X%, Memory: X%, DB connections: X of Y]

Growth assumptions:
- Expected traffic growth: [X% per month / flat / specific event-driven spike]
- Expected data growth: [GB/month stored in database or object storage]
- Planned product launches: [any events that will cause sudden spikes]

Constraints:
- SLO: [availability target, latency SLO]
- Budget ceiling: [$X/month max]
- Cloud provider: [AWS / GCP / Azure]
- Existing commitments: [any reserved instances or savings plans already purchased]

Produce:

## 1. Capacity forecast
Projected resource needs at: [3 months out / 6 months / 12 months]
- Compute: current vs. needed
- Memory: current vs. needed
- Database: storage and IOPS growth
- Bandwidth / data transfer costs
- CDN or caching layer impact

## 2. Scaling triggers
At what metric threshold should we scale?
- CPU > X% sustained for Y minutes → scale out by Z replicas
- Memory > X% → vertical scale to next tier or add swap
- DB connections > X% of max → consider connection pooling (PgBouncer) or read replica

## 3. Cost projection
| Month | Compute | Database | Storage | Bandwidth | Total |
|---|---|---|---|---|---|
| Now | $X | $X | $X | $X | $X |
| +3mo | $X | $X | $X | $X | $X |
| +6mo | $X | $X | $X | $X | $X |
| +12mo | $X | $X | $X | $X | $X |

## 4. Scaling recommendations
Concrete actions in order:
1. [What to do now — immediate action]
2. [What to do in 30-60 days]
3. [What to plan for at 6 months]

## 5. Cost optimisation opportunities
Savings available without reducing capacity:
- Reserved instances / savings plans: $X/month saved if purchased now
- Rightsizing: [specific instances that are over-provisioned]
- Storage tiering: [any data that can move to cheaper storage]
- Caching: [what can be cached to reduce DB load and compute cost]

Traffic-based scaling model

Build a scaling model for [SERVICE] based on traffic patterns.

Current traffic data:
- Average RPS (requests per second): [X]
- Peak RPS (highest observed): [X]
- Daily traffic pattern: [flat / morning peak / evening peak / bursty]
- Weekly pattern: [weekday-heavy / weekend-heavy / flat]

Service characteristics:
- Average request latency: [Xms at current load]
- CPU per request (approximate): [X% per pod per 100 RPS]
- Memory per request: [X MB working set per pod]
- Stateless or stateful: [stateless = easy to scale horizontally]

Scaling model output:

For each RPS level:
| RPS | Pods needed | CPU headroom | Latency estimate | Cost/month |
|---|---|---|---|---|
| [Current: X] | [Y pods] | [X% headroom] | [Xms] | $X |
| [2x growth] | | | | |
| [5x growth] | | | | |
| [10x growth] | | | | |

Horizontal scaling rules:
- Scale out when: CPU > [X]% for [Y] minutes OR RPS > [Z]
- Scale in when: CPU < [X]% for [Y] minutes AND RPS < [Z]
- Minimum pods: [N] (for availability during scaling events)
- Maximum pods: [N] (cost ceiling or account limit)

HPA (Horizontal Pod Autoscaler) config for Kubernetes:
```yaml
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: [service-name]
  namespace: [namespace]
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: [service-name]
  minReplicas: [N]
  maxReplicas: [N]
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 70
  - type: Resource
    resource:
      name: memory
      target:
        type: Utilization
        averageUtilization: 80

Generate the scaling model for my service.

### Database capacity planning

Plan database capacity for [SERVICE] over [N] months.

Current state:

• Database: [PostgreSQL / MySQL / MongoDB / DynamoDB / etc.]
• Instance: [current instance type and size]
• Storage: [current used / total provisioned]
• Connections: [current active connections / max connections]
• Largest tables: [name: X GB, name: Y GB]
• Query patterns: [read-heavy 80/20 / write-heavy / balanced]
• Backup retention: [X days]

Growth inputs:

• New data per day: [X GB / X rows in largest table]
• Monthly growth rate: [X%]
• Any planned data migrations or schema changes: [describe]

Database capacity plan output:

Storage forecast

Storage alert thresholds:

• Amber: storage > 70% full → plan upgrade
• Red: storage > 85% full → upgrade within 1 week

Connection capacity

Current max connections for [instance type]: [N] Current usage: [X connections, X% of max] Connection pool recommendation:

If using PgBouncer or RDS Proxy:

• Pool size per application instance: [N]
• Max clients: [N]
• Pool mode: [transaction / session — transaction recommended for stateless APIs]

Instance upgrade trigger

Upgrade instance when:

• Average CPU > 70% for > 30 minutes daily
• Free storage < 20% of total
• Read IOPS > 80% of provisioned IOPS consistently
• P99 query latency > [X]ms for top 10 queries

Next instance tier: [current] → [recommended next] at [X months] Cost delta: $X/month additional

Read replica consideration

Add a read replica when:

• Read:write ratio > 5:1
• Reporting/analytics queries are impacting primary performance
• Primary CPU is being driven by reads, not writes

Read replica cost: $X/month (same instance type as primary) Connection routing: [describe how to route reads vs. writes in application code]

### Launch capacity plan

Build a launch capacity plan for [PRODUCT / FEATURE / EVENT].

Launch details:

• What's launching: [describe]
• Expected launch date: [DATE]
• Traffic scenario (choose one or model all three):
  • Conservative: [X% of current traffic increase]
  • Base case: [X users in first 48 hours]
  • Optimistic: [X users, featured in [media / App Store / Product Hunt]]

Current infrastructure:

• Compute: [describe]
• Database: [describe]
• CDN / cache: [describe]
• Current capacity: [what's the maximum RPS the system can handle today?]

Launch plan output:

Pre-launch checklist (infrastructure)

• Load test at [2x / 5x / 10x] expected peak traffic — document results
• Confirm auto-scaling is configured and tested
• Cache warm-up plan for static assets and common queries
• Database connection pool sized for peak connections
• CDN cache rules reviewed for new pages/assets
• Monitoring dashboards set up for launch day
• On-call engineer identified and briefed on runbook
• Rollback plan documented and tested

Traffic scenarios and infrastructure needs

Launch day procedure

T-24h: pre-scale compute to [N] pods (don't wait for autoscaler) T-4h: warm CDN cache for all new pages T-0: post in #engineering and tag on-call with launch dashboard link T+1h: check error rates, latency, DB connections — compare to baseline T+24h: review actual traffic vs. forecast, resize if over-provisioned

Cost for launch period

Extra cost for [7 days of pre-scaled infrastructure]: $X Rollback to normal provisioning after: [DATE] if traffic stabilises below [X] RPS

### Cloud cost optimisation analysis

Analyse my cloud costs and find savings opportunities.

Current monthly bill: [$X total] Breakdown:

• Compute (EC2 / GKE nodes / Cloud Run): $X
• Database (RDS / Cloud SQL / Firestore): $X
• Storage (S3 / GCS / Azure Blob): $X
• Data transfer / CDN: $X
• Other (Lambda, SQS, monitoring, etc.): $X

Infrastructure inventory:

• Instances/nodes: [list with sizes and average utilisation]
• Databases: [list with sizes and average utilisation]
• Storage buckets: [total stored, access patterns]
• Any reserved instances or savings plans already in place: [list]

Analyse by category:

COMPUTE RIGHTSIZING:

• Instances with average CPU < 20%: candidates for downsizing
• Memory utilisation: over-provisioned instances
• Estimated savings from rightsizing: $X/month

RESERVED INSTANCES / SAVINGS PLANS:

• Break-even analysis: if we commit to [N]x [instance type] for 1 year, we save $X vs. on-demand
• Recommendation: which instances to reserve now vs. keep on-demand

STORAGE COST REDUCTION:

• S3 Intelligent Tiering for infrequently accessed data
• Log retention policy: reduce from [N] to [M] days → save $X/month
• Identify orphaned EBS volumes or snapshots: [common waste source]

DATABASE OPTIMISATION:

• Multi-AZ vs. single-AZ for dev/staging: save $X/month
• Aurora Serverless for variable workloads: break-even at [X hours/day utilisation]
• Read replicas that can be removed or downsized

Produce: ranked list of savings opportunities by monthly dollar impact, with implementation effort (low / medium / high).

## Example

**User:** We're planning to open-source a tool and expect it to be featured on Product Hunt next month. Currently we have 2 t3.medium EC2 instances behind an ALB, serving 500 RPS at 45% CPU. We expect 5-10x traffic spike on launch day. Monthly bill is $220.

**Output (excerpt):**

```markdown
# Capacity Plan: Product Hunt Launch

## Current baseline
2x t3.medium (2 vCPU, 4GB RAM) — 500 RPS at 45% CPU.
Estimated max capacity: ~1,100 RPS before CPU saturation.

## Traffic scenarios
| Scenario | Peak RPS | Required instances | Headroom |
|---|---|---|---|
| Conservative (5x) | 2,500 | 5x t3.medium | 20% |
| Base case (7x) | 3,500 | 7x t3.medium | 10% |
| Optimistic (10x+) | 5,000+ | 10x t3.medium or 5x t3.large | 15% |

## Pre-launch actions (by priority)

**Now (today):**
- Enable EC2 Auto Scaling with min=2, max=12, scale-out at CPU>60% for 3 minutes
- Set scale-in cooldown to 15 minutes (prevents thrashing after spike)
- Verify ALB health check is correctly configured and responds < 2s

**T-48h before launch:**
- Pre-scale to 6 instances manually (don't rely on autoscaler during the spike — it lags 3-5 minutes)
- Run a load test to 3,500 RPS using k6 or Locust — confirm latency stays < 200ms

**T-4h:**
- Warm CloudFront cache for all static assets on the new pages
- If serving any database-backed content: review cache-control headers

**Launch day cost:**
7 days of 6x t3.medium pre-scaled: ~$90 additional
If you hit 10x and scale to 10 instances: ~$150 additional for the week
Recommend: pre-scale, watch, scale down after 48-72h when traffic normalises.

**What to watch on launch day:**
- ALB RequestCount (not just RPS at your app — ALB is the leading indicator)
- Target group healthy host count (should stay at pre-scaled N throughout)
- DB connections — t3.medium can handle ~50 connections each; at 10 instances that's 500 connections
- If using RDS: check FreeableMemory and DatabaseConnections metrics