NALSD Framework

Non-Abstract Large System Design

Capacity & Release | Technical Operations Excellence

4
Essential Questions
N+2
Headroom Target
2x
Load Test Target
30d
Forecast Window

The 4 Essential Questions

1. Is it possible?

Can we build it at all?

2. Can we do better?

Optimize design choices

3. Is it feasible?

Cost, time, resources

4. Is it resilient?

Graceful degradation

Capacity Planning Process

StepActivity
1. Demand ForecastHistorical trends + growth models
2. Supply AnalysisCurrent capacity, bottlenecks
3. Gap AssessmentWhere will we run out?
4. Headroom PlanningN+1 min, N+2 for critical

Load Testing Strategy

Test TypePurposeTarget
BaselineNormal loadCurrent traffic
StressFind limits2x expected
SpikeSudden surge10x for 30s
SoakLeaks, drift24-48 hours

Design Trade-offs

DimensionTrade-off
Consistencyvs. Availability (CAP)
Latencyvs. Throughput
Costvs. Resilience
Complexityvs. Maintainability

Capacity Metrics

MetricTarget
CPU Utilization<70% avg, <90% peak
Memory<80% avg, <95% peak
Disk I/O<70% queue depth
Network<60% bandwidth

Leave headroom for traffic spikes and incidents

Scaling Strategies

TypeWhen to Use
VerticalSimple, single-instance
HorizontalStateless, distributed
Auto-scalingVariable traffic patterns
PredictiveKnown events (launches)

Forecasting Inputs

  • Historical trends: Past 90+ days growth
  • Seasonality: Day/week/month patterns
  • Business events: Launches, campaigns
  • External factors: Market trends

Warning Signs

  • Utilization >80% sustained
  • P99 latency creeping up
  • Queue depths growing
  • Error rates increasing

Plan for 2x

Capacity planning is cheaper than outages.