dns - caching DNS resolver for Go HTTP clients

The Go HTTP client does not cache DNS lookups. This means every outbound request incurs a DNS lookup. Usually, the host operating system caches DNS lookups. However, for small containers, like distroless, the host OS doesn't cache DNS lookups.

Get started

Create a new http.Client with a dns.Resolver as the http.Transport's DialContext function. The DialContext function is called for every new outbound connection.

package main

import (
	"net/http"

	"github.com/jschaf/dns"
)

var (
	dnsCache      = &dns.Cache{}
	cachingClient = &http.Client{
		Transport: &http.Transport{
			DialContext: (&net.Dialer{
				Resolver: dnsCache.Resolver(),
			}).DialContext,
		},
	}
)

// To replace the global, default HTTP client, use the `http.DefaultClient`
// variable.
func init() {
	http.DefaultClient = cachingClient
}

Pitch

Why should you use dns.Resolver?

• Increase the performance of HTTP clients, reducing unnecessary round trips for DNS lookups.

• Avoid external dependencies, like separate a caching DNS resolver.

Anti-pitch

I'd like to try to convince you why you shouldn't use pggen. Often, this is more revealing than the pitch.

• Your host OS already caches DNS lookups. In this case, the extra complexity of one of the two hard problems in computer science (caching) is not worth it.

• You have enough operational expertise to run a caching DNS resolver somewhere in your stack. In Kubernetes, this is probably NodeLocal DNSCache.

• A standalone caching DNS resolver reduces the total number of DNS lookups across all clients, not just HTTP clients. This is a more efficient use of resources.