🚀 Advanced & Capstone · Days 25–30
Day 26: Observability Correlation
Objective
Run a test while watching APM / metrics dashboards side-by-side.
Scenario
Open your APM or infrastructure dashboard in one window. Run your load test in another. When latency spikes in the tool, find the matching spike in CPU, DB, or GC metrics.
Metrics to Watch
When It Clicks
The tool says 'slow'; observability says 'why.'
Solution
Open Datadog, Grafana, New Relic, or your APM of choice in one window. Start the load test. When JMeter or k6 shows a latency spike, immediately look for the matching spike in: (1) CPU - compute-bound, (2) DB query time - database-bound, (3) GC pause duration - memory-bound, (4) downstream service latency - dependency-bound. The most useful APM feature for this is a distributed trace waterfall: it shows exactly which span is consuming the most wall-clock time within a single slow request.
Reflection
Which infrastructure metric most clearly explained your slowest transaction?
Deliverable
A documented test run with correlated tool + APM screenshots.
⚠️ 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.