A production e-commerce application went down when a Docker container entered a crash loop — restarting every 3 minutes due to OOM (Out of Memory) kills. The client's team could not identify the cause for 4 hours. Optimum Web's senior engineer connected via SSH, identified the root cause (Node.js worker process leaking memory through an unbounded event listener array), and fixed it in 47 minutes for $99 fixed price. The application has been stable for 5 months since, with zero OOM events.
This case study shows exactly what the crash looked like, how we diagnosed it, what the fix was, and how to recognize the same problem on your server.
The Problem: "Container Keeps Restarting Every 3 Minutes"
Friday, 5:17 PM. A logistics SaaS company in Germany noticed their tracking dashboard was down. Docker logs showed the pattern immediately:
app_worker | Killed
app_worker | OOM: Kill process 1 (node) score 987
app_worker exited with code 137
app_worker | Starting...
# ... repeats every 2-3 minutesExit code 137 = killed by OOM (Out of Memory). The container was configured with a 512MB memory limit. Every 2–3 minutes, the Node.js process consumed all 512MB, was killed by the kernel, restarted, and the cycle repeated.
What the client's team tried (and why it didn't work):
| Attempt | Result |
|---|---|
| Increase memory limit to 1GB | Crash shifted to every 5 minutes — same problem, more RAM to fill |
| Restart the entire Docker stack | Same crash loop after 3 minutes |
| Roll back to previous Docker image | Same crash — the bug was in a data dependency, not code version |
After 4 hours of downtime, they contacted us.
Why This Happens
Memory leaks in Node.js are notoriously difficult to diagnose because:
JavaScript uses garbage collection — developers assume memory is managed automatically. It is, but only when there are no references to an object. If your code keeps a reference, garbage collection is blocked.
Leaks only appear under production load. Local development handles 5–10 concurrent connections. Production has 1,000+. The leak grows slowly at low traffic, then triggers frequently under load.
OOM kill is silent. The kernel kills the process without warning. Application logs show nothing — the next log line is the container restarting. You never see the root cause in logs.
Common Node.js leak sources: unbounded arrays growing with every request, event listeners not removed on disconnect, global caches without eviction policy, circular references preventing garbage collection.
Our Diagnosis (First 12 Minutes)
# 1. Check which container is crashing
$ docker ps -a --format "{{.Names}}: {{.Status}}"
app_worker: Restarting (137) 45 seconds ago
# 2. Memory at the moment of crash
$ docker stats --no-stream app_worker
# MEM USAGE: 498MB / 512MB — at limit
# 3. Heap growth pattern
$ docker exec app_worker node -e "console.log(process.memoryUsage())"
# heapUsed: 487MB — almost all memory is heap
# 4. Generate heap snapshot via Chrome DevTools
# Found: Array "eventListeners" — 340,000 entries (growing ~1,000/min)Root cause: A WebSocket handler was adding an event listener on every new connection but never removing it on disconnect. After 340,000 connections over 5 hours of production traffic, the listener array consumed all available memory.
The Fix (35 Minutes)
// BEFORE (bug):
socket.on('connection', (ws) => {
process.on('SIGTERM', () => ws.close()); // Added every connection, never removed
});
// AFTER (fix):
socket.on('connection', (ws) => {
const cleanup = () => ws.close();
process.once('SIGTERM', cleanup); // Auto-removes after firing
ws.on('close', () => {
process.removeListener('SIGTERM', cleanup); // Explicit cleanup on disconnect
});
});Additionally applied:
- Set --max-old-space-size=384 to trigger GC pressure earlier, before reaching the container limit - Added memory monitoring alert (Telegram notification when heap > 80%) - Configured Docker restart policy with exponential backoff delay
→ [Fix My Docker — $99](/fixed-price/fix-docker-issues#checkout) · Root cause diagnosis included · 14-day warranty
The Result
| Metric | Before | After |
|---|---|---|
| Container restarts per hour | 20–30 | 0 |
| Memory usage (steady state) | 498MB → OOM every 3 min | 180–220MB stable |
| Downtime | 4 hours (and counting) | 0 (5 months stable) |
| Time to resolution | 4+ hours (no result) | 47 minutes |
Cost & Timeline
| Item | Detail |
|---|---|
| Service | OW-BUG-01: Fix Docker & Docker Compose Issues |
| Price | $99 fixed |
| Actual time | 47 minutes (SSH to resolution) |
| Engineer | Senior Node.js / Docker specialist |
| Included | Root cause diagnosis, code fix, memory monitoring, Docker config update |
| Warranty | 14 days |
🐛 Docker Container Crashing? We Fix It Same Day — $99.
OOM kills, network errors, permission denied, crash loops — root cause diagnosed and fixed. Not just restarted.
- ✓SSH diagnostic within 24 hours of order
- ✓Root cause identification (heap snapshot, logs, traces)
- ✓Code fix included (not just Docker restart)
- ✓Memory monitoring setup
- ✓Docker restart policy configuration
- ✓14-day warranty
$99 · Service ID: OW-BUG-01 · 14-day warranty
Fix My Docker — $99 →Production Completely Down?
If your production is down right now and every minute costs you revenue, use [Emergency Server Recovery — $199](/fixed-price/quickfix-server-recovery#checkout) instead. Response within 1–4 hours. We SSH in, stabilize production first, diagnose root cause second.
Could This Be Your Problem? (5 Warning Signs)
- Docker container restarts periodically (check docker ps -a for exit code 137)
- Memory usage climbs steadily then drops to zero (the restart cycle)
- The problem only appears in production, never in local development
- Increasing container memory limit only delays the crash by minutes
- Application logs show no errors before the crash — OOM kill is silent
If 2 or more apply, you likely have a memory leak.
→ [Fix Docker Issues — $99](/fixed-price/fix-docker-issues#checkout) · Root cause + code fix · 14-day warranty → [Emergency Recovery — $199](/fixed-price/quickfix-server-recovery#checkout) · 1–4 hour response · Production down now