🚀 Advanced & Capstone · Days 25–30
Day 28: Capacity & Scalability Modeling
Objective
Use your test results to estimate maximum safe capacity and headroom.
Scenario
From your step-load data (Day 11) and saturation point (Day 21), model how many users the system can safely handle. Apply Little's Law if appropriate.
Metrics to Watch
When It Clicks
Data, not guesses, sizes infrastructure.
Solution
From your Day 11 step-load data you have throughput at each user count. From Day 21 you have the saturation point. Apply Little's Law: N = X * R, where N = concurrent users, X = throughput (req/s), R = mean response time (s). Solve for X_max at your observed saturation. Headroom % = (X_max - X_current) / X_max. If current production throughput is 80% of X_max, you have 20% headroom. The resource that hits its limit first (CPU, DB connections, memory) at X_max is your first failure point under a traffic doubling.
Reflection
If production traffic doubled tomorrow, what would fail first?
Deliverable
A capacity model / spreadsheet based on your test data.
⚠️ Never run load tests against infrastructure you do not own or have explicit written permission to test. Always use a dedicated test environment. Unauthorized load injection can cause outages, trigger legal liability, and violate terms of service.