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typescript.sync_dns_lookup

Stability High

Detects synchronous DNS lookups that block the Node.js event loop.

Why It Matters

Sync DNS lookups:

Block event loop — All requests stall
Unpredictable latency — DNS can take seconds
Causes timeouts — Other operations starved

Example

// ❌ Before (blocking DNS lookup)
import { lookupSync } from 'dns';

function getHostIp(host: string): string {
  return lookupSync(host); // Blocks!
}

// ✅ After (async DNS resolution)
import dns from 'dns/promises';

async function getHostIp(host: string): Promise<string> {
  const result = await dns.lookup(host);
  return result.address;
}

What Unfault Detects

dns.lookupSync usage
Blocking network resolution
Sync operations in async context

Auto-Fix

Unfault can convert to async dns.lookup.