Bun npm Compatibility Failures: Production Implementation Guide

Critical Runtime Requirements

CPU Architecture Dependencies

Hard Requirement: AVX2 CPU instructions (Intel 2013+ / AMD 2015+)

• Failure Mode: Immediate crash with "Illegal instruction (core dumped)"
• Affected Infrastructure: AWS EC2 t2/t3 instances, Docker on pre-2014 hardware, older CI runners
• Detection: grep -o 'avx2' /proc/cpuinfo | head -1
• No Software Workaround: Must upgrade hardware or use Node.js

Container Signal Handling

Critical Issue: Exit code 143 (SIGTERM not handled)

• Root Cause: Bun doesn't receive Docker SIGTERM signals without --init flag
• Impact: Database connections not closed, requests killed mid-processing, corrupted app state
• Fix: Add --init flag to Docker CMD: CMD ["bun", "--init", "run", "start"]
• Alternative: Use tini: ENTRYPOINT ["/sbin/tini", "--"]

Package Compatibility Matrix

Native Modules (Complete Incompatibility)

Reason: C++ addons use Node.js N-API, Bun doesn't implement N-API

Package	Status	Bun Alternative	Migration Effort
sharp	Breaks	ImageMagick service	High - separate container
bcrypt	Breaks	import { hash } from 'bun'	Low - direct replacement
sqlite3	Breaks	import { Database } from 'bun:sqlite'	Medium - API changes
node-canvas	Breaks	None available	High - architectural change
fsevents	Breaks	bun:fs watcher	Medium - API changes

Module Resolution Failures

Root Cause: ESM-first resolution vs Node.js CommonJS resolution

Problematic Packages:

• AWS SDK v3: Export maps incompatible
• Prisma client: Conditional exports fail
• GraphQL tools: Module resolution conflicts
• styled-components: Babel dependencies break

Detection Pattern:

Error: Cannot resolve "./lib/index.js" from "./node_modules/some-package/package.json"

Workaround:

// Instead of package exports (breaks in Bun)
import { something } from 'package-name';

// Use direct imports (works in both)
import { something } from 'package-name/lib/something.js';

Memory Management Differences

JavaScriptCore vs V8 Impact

Critical Difference: Different garbage collection timing and patterns

• V8 (Node.js): Generational collection with frequent cleanup
• JSC (Bun): Retreating wavefront concurrent GC with longer object lifetimes

Memory Leak Patterns

High-Risk Code Patterns:

// DANGEROUS: Map grows forever in JSC
const requestCache = new Map();
app.get('/api/*', (req, res) => {
  requestCache.set(req.url, { timestamp: Date.now(), response: data });
  // In Node: GC cleans regularly
  // In Bun: References persist longer, causes OOM
});

Safe Patterns:

// Use WeakMap or implement explicit cleanup
const requestCache = new Map();
setInterval(() => {
  const cutoff = Date.now() - 300000;
  for (const [key, value] of requestCache) {
    if (value.timestamp < cutoff) {
      requestCache.delete(key);
    }
  }
}, 60000);

Production Memory Monitoring

import { heapStats } from 'bun:jsc';

const memoryAlert = () => {
  const stats = heapStats();
  const rss = process.memoryUsage.rss();
  const rssMB = Math.round(rss / 1024 / 1024);

  if (rssMB > 800) { // Adjust threshold for your application
    console.error('Memory usage critical - investigate memory leaks');
    // Restart containers at 1GB to prevent OOM kills
  }
};

setInterval(memoryAlert, 30000);

Production Deployment Failures

Environment Variable Loading

Issue: Different timing than Node.js process.env

// Problematic (timing issues)
const config = {
  port: process.env.PORT || 3000
};

// Correct for Bun
import { env } from 'bun';
const config = {
  port: env.PORT || 3000
};

Network and HTTP Differences

Timeout Handling:

// Bun-specific timeout pattern
const controller = new AbortController();
setTimeout(() => controller.abort(), 5000);

const response = await fetch(url, {
  signal: controller.signal
});

Connection Pool Monitoring:

const activeConnections = new Set();

async function makeRequest(url) {
  const id = Math.random().toString(36);
  activeConnections.add(id);

  try {
    return await fetch(url);
  } finally {
    activeConnections.delete(id);
    if (activeConnections.size > 100) {
      console.warn(`High connection count: ${activeConnections.size}`);
    }
  }
}

Platform-Specific Issues

Windows Compatibility

File Permission Failures:

• Windows Defender flags fast file operations as malware
• NTFS symlink permissions differ from Unix
• PATH length limits (260 chars) break deep node_modules

Solutions:

1. Exclude project from Windows Defender: Add-MpPreference -ExclusionPath "C:\dev\your-project"
2. Enable long paths (admin required): New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem" -Name "LongPathsEnabled" -Value 1
3. Recommended: Use WSL2 instead of native Windows

Corporate Network Issues

DNS Resolution: Bun doesn't respect some corporate DNS settings that Node.js handles
Workaround: Explicit DNS resolution checks and IP fallbacks

Emergency Response Procedures

Immediate Triage Patterns

1. Exit 143: Signal handling issue → Add --init flag
2. "Cannot find module": Module resolution → Use direct imports
3. "Illegal instruction": CPU incompatibility → Upgrade hardware or rollback
4. Memory exhaustion: JSC GC differences → Restart + increase limits

Rollback Strategy

Priority Order:

1. Docker tag rollback (2-5 minutes): kubectl set image deployment/api api=your-app:node-v1.2.3
2. Feature flag toggle (10 minutes): Runtime switching between Bun/Node
3. Partial service rollback (15+ minutes): Critical services to Node, keep others on Bun

Live Debugging Tools

// Emergency memory monitoring
global.debugMemory = () => {
  const stats = heapStats();
  console.log({
    heap_mb: Math.round(stats.heapSize / 1024 / 1024),
    rss_mb: Math.round(process.memoryUsage.rss() / 1024 / 1024)
  });
  if (global.gc) global.gc(); // Force GC if available
};

Decision Matrix: When to Use Bun

Bun Appropriate When:

• New projects (no migration complexity)
• Mainstream dependencies only
• Fast startup critical (serverless/edge)
• Team has debugging capacity
• Performance gains justify risk

Stay with Node.js When:

• Native modules required
• Existing stable deployment
• Limited debugging time
• Corporate/regulated environment
• Team lacks Bun expertise

Resource Investment Requirements

• Debugging Time: 3x Node.js troubleshooting time
• Migration Effort: 2-4 weeks for medium projects
• Expertise Required: Understanding of JSC vs V8 differences
• Monitoring Overhead: Additional memory/signal monitoring needed

Critical Warnings

1. No Native Module Support: Plan architectural changes for image processing, encryption, databases
2. Production Debugging Complexity: Error messages often unhelpful, limited community knowledge
3. Hardware Dependencies: Modern CPU required, incompatible with older infrastructure
4. Memory Pattern Changes: Existing Node.js memory patterns may leak in Bun
5. Container Orchestration: Requires signal handling fixes for proper shutdown

Testing Requirements

• Validate CPU compatibility on all deployment targets
• Test all dependencies for native module usage
• Verify container signal handling with load testing
• Monitor memory usage patterns under production load
• Implement rollback procedures and test execution time
• Train team on Bun-specific debugging techniques