Node DNS Caching: Stop Micro-Outages From Brief Resolver Blips

// src/dns-agent.ts
import CacheableLookup from "cacheable-lookup";
import { Agent, setGlobalDispatcher } from "undici";
import { Resolver } from "node:dns";

const resolver = new Resolver();
resolver.setServers(process.env.DNS_SERVERS?.split(",") ?? ["10.0.0.2"]);

const cacheable = new CacheableLookup({
 maxTtl: 30, // ✅ clamp runaway TTLs
 errorTtl: 2, // ✅ short negative cache
 resolver,
});

export const dispatcher = new Agent({
 connect: {
 lookup: cacheable.lookup.bind(cacheable) as any,
 timeout: 3_000,
 },
 keepAliveTimeout: 30_000,
 connections: 32,
});

setGlobalDispatcher(dispatcher);

// ❌ New Agent per request + default lookup — amplifies every blip
const res = await fetch(url); // default DNS, no shared cache

// src/stale-dns.ts
type Entry = { address: string; family: 4 | 6; expires: number; staleUntil: number };
const map = new Map<string, Entry>();

export async function lookupCached(host: string, lookup: typeof import("node:dns").promises.lookup) {
 const now = Date.now();
 const hit = map.get(host);
 if (hit && hit.expires > now) return { address: hit.address, family: hit.family };
 try {
 const r = await lookup(host, { verbatim: true });
 map.set(host, {
 address: r.address,
 family: r.family as 4 | 6,
 expires: now + 15_000,
 staleUntil: now + 60_000,
 });
 return r;
 } catch (err) {
 // ✅ Serve stale for a bounded window instead of failing open forever
 if (hit && hit.staleUntil > now) {
 metrics.increment("dns.stale_served");
 return { address: hit.address, family: hit.family };
 }
 throw err;
 }
}

# ✅ Prove resolver latency in staging
dig @$COREDNS api.internal.svc.cluster.local +stats
# Alarm on dns.lookup error rate and p99 duration