The Post-Mortem: Root Cause Analysis for Java Developers
Engineering is Learning from Failure
Production incidents are inevitable. What defines a senior engineer is not the ability to avoid them, but the ability to diagnose them and ensure they never happen again. This guide covers the Root Cause Analysis (RCA) process.
Core Concepts
1. The Incident Lifecycle
- Detection: Monitoring/Alerting (e.g., App Insights, Prometheus).
- Containment: Quick fix to restore service (e.g., restart, rollback).
- Resolution: Long-term fix for the root cause.
2. The “5 Whys” Technique
A non-technical but powerful tool for digging deep.
- Problem: The Java API is slow.
- Why?: The DB connection pool is exhausted.
- Why?: Queries are taking 5 seconds to complete.
- Why?: There is no index on the
statuscolumn. - Why?: We didn’t have performance testing in the CI/CD pipeline. (Root Cause)
Practice Exercise: Drafting a Mock RCA
Incident: High CPU usage causing 503 Service Unavailable errors.
RCA Document Template
| Section | Content |
|---|---|
| Title | High CPU - Memory Leak in Reporting Service |
| Severity | P1 (Critical) |
| Impact | 5,000 users unable to view reports for 45 minutes. |
| Timeline | 10:00 (Alert), 10:15 (Investigation), 10:45 (Service Restarted). |
| Root Cause | A static ArrayList was accumulating User objects in a recurring background task, slowly filling the heap and causing the GC to use 90% of the CPU trying to free space. |
| Preventative Actions | 1. Implement HeapUsage alerts in Grafana. 2. Use WeakReference for the cache. 3. Add a memory-leak check to the PR review checklist. |
Technical Tools for RCA in Java
- JFR (Java Flight Recorder): Extremely low-overhead profiling that records JVM events. Great for “What happened at 2 AM?”.
- Heap Dumps: Captures every object in memory. Use tools like Eclipse MAT to find who is “holding” onto memory.
- Thread Dumps: Shows what every thread is doing. Essential for diagnosing deadlocks or thread-starvation.
The “Blameless” Culture
The goal of an RCA is to find “What” went wrong, not “Who” did it. If engineers feel blamed, they will hide mistakes, making the system more fragile over time. Focus on the Systemic Failure that allowed the mistake to happen.
Summary
RCA is the highest form of professional technical communication. By documenting failures clearly and proposing actionable preventative measures, you transform an expensive outage into a valuable investment in the platform’s stability.