go-dnsmasq

this is a fork of janeczku/go-dnsmasq and Doout/go-dnsmasq.

go-dnsmasq is a lightweight DNS caching server/forwarder with minimal filesystem and runtime overhead.

Dynamic Name resolving

go-dnsmasq provides pluggable DNS resolve function.

package main

import (
	"math/rand"
	"net"
	"os"
	"time"

	"github.com/miekg/dns"
	"github.com/soulteary/go-dnsmasq/pkg"
	"github.com/soulteary/go-dnsmasq/pkg/log"
	"github.com/soulteary/go-dnsmasq/pkg/resolvconf"
	"github.com/soulteary/go-dnsmasq/pkg/server"
)

// return 1.1.1.1 randomly
func return1111() server.PluggableFunc {
	return func(m *dns.Msg, q dns.Question, targetName string, isTCP bool) (*dns.Msg, error) {
		if rand.Intn(10) > 4 {
			return nil, nil
		}
		r := new(dns.A)
		r.Hdr = dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA,
			Class: dns.ClassINET, Ttl: 10}
		r.A = net.ParseIP("1.1.1.1")
		m.Answer = append(m.Answer, r)
		return m, nil
	}
}

func main() {
	log.New("debug")
	listen, err := server.CreateListenAddress("0.0.0.0:53")
	if err != nil {
		return
	}
	sconf := &server.Config{
		DnsAddr:         listen,
		DefaultResolver: true,
		Hostsfile:       "/etc/hosts",
		ReadTimeout:     time.Second,
	}
	resolvconf.Clean()
	if err := server.ResolvConf(sconf, true); err != nil {
		if !os.IsNotExist(err) {
			log.Errorf("parsing resolve.conf: %w", err)
			return
		}
	}
	pf := return1111()
	s, err := pkg.BuildServer(sconf, &pf, "")
	if err != nil {
		return
	}
	log.Error(pkg.Run(s))
}

Application examples:

• Caching DNS server/forwarder in a local network
• Container/Host DNS cache
• DNS proxy providing DNS search capabilities to musl-libc based clients, particularly Alpine Linux

Features

• Automatically set upstream nameservers and search domains from resolv.conf
• Insert itself into the host's /etc/resolv.conf on start
• Serve static A/AAAA records from a hosts file
• Provide DNS response caching
• Replicate the search domain treatment not supported by musl-libc based Linux distributions
• Supports virtually unlimited number of search paths and nameservers (related Kubernetes article)
• Configure stubzones (different nameserver for specific domains)
• Round-robin of DNS records
• Send server metrics to Graphite and StatHat
• Configuration through both command line flags and environment variables

Resolve logic

DNS queries are resolved in the style of the GNU libc resolver:

• The first nameserver (as listed in resolv.conf or configured by --nameservers) is always queried first, additional servers are considered fallbacks
• Multiple search domains are tried in the order they are configured.
• Single-label queries (e.g.: "redis-service") are always qualified with the search domains
• Multi-label queries (ndots >= 1) are first tried as absolute names before qualifying them with the search domains

Command-line options / environment variables

Flag	Description	Default	Environment vars
--listen, -l	Address to listen on host[:port]	127.0.0.1:53	$DNSMASQ_LISTEN
--default-resolver, -d	Update resolv.conf to make go-dnsmasq the host's nameserver	False	$DNSMASQ_DEFAULT
--nameservers, -n	Comma delimited list of nameservers host[:port]. IPv6 literal address must be enclosed in brackets. (supersedes etc/resolv.conf)	-	$DNSMASQ_SERVERS
--stubzones, -z	Use different nameservers for given domains. Can be passed multiple times. domain[,domain]/host[:port][,host[:port]]	-	$DNSMASQ_STUB
--hostsfile, -f	Path to a hosts file (e.g. ‘/etc/hosts‘)	-	$DNSMASQ_HOSTSFILE
--hostsfiles, --fs	Path to a hosts file directory (e.g. ‘/etc/hosts‘)	-	$DNSMASQ_DIRECTORY_HOSTSFILES
--hostsfile-poll, -p	How frequently to poll hosts file for changes (seconds, ‘0‘ to disable)	0	$DNSMASQ_POLL
--search-domains, -s	Comma delimited list of search domains domain[,domain] (supersedes /etc/resolv.conf)	-	$DNSMASQ_SEARCH_DOMAINS
--enable-search, -search	Qualify names with search domains to resolve queries	False	$DNSMASQ_ENABLE_SEARCH
--rcache, -r	Capacity of the response cache (‘0‘ disables caching)	0	$DNSMASQ_RCACHE
--rcache-ttl	TTL for entries in the response cache	60	$DNSMASQ_RCACHE_TTL
--no-rec	Disable forwarding of queries to upstream nameservers	False	$DNSMASQ_NOREC
--fwd-ndots	Number of dots a name must have before the query is forwarded	0	$DNSMASQ_FWD_NDOTS
--ndots	Number of dots a name must have before making an initial absolute query (supersedes /etc/resolv.conf)	1	$DNSMASQ_NDOTS
--round-robin	Enable round robin of A/AAAA records	False	$DNSMASQ_RR
--verbose	Enable verbose logging	False	$DNSMASQ_VERBOSE
--help, -h	Show help
--version, -v	Print the version

Enable Graphite/StatHat metrics

EnvVar: GRAPHITE_SERVER
Default:
Set to the host:port of the Graphite server

EnvVar: GRAPHITE_PREFIX
Default: go-dnsmasq
Set a custom prefix for Graphite metrics

EnvVar: STATHAT_USER
Default:
Set to your StatHat account email address

Usage

Run from the command line

Download the binary for your OS from the releases page.

go-dnsmasq is available in two versions. The minimal version (go-dnsmasq-min) has a lower memory footprint but doesn't have caching, stats reporting and systemd support.

   sudo ./go-dnsmasq [options]

Run as a Docker container

Docker Hub trusted builds are available.

docker run -d -p 53:53/udp -p 53:53 soulteary/go-dnsmasq

You can pass go-dnsmasq configuration parameters by setting the corresponding environmental variables with Docker's -e flag.

Run as a Docker container with docker-compose

Docker Hub trusted builds are available.

version: "3"
services:
  dns:
    image: soulteary/go-dnsmasq
    command: dnsmasq -l 0.0.0.0:53 -f /hosts.conf -p 1s --nameservers 8.8.8.8:53 --log-level info
    restart: always
    ports:
      - "53:53/udp"
      - "53:53/tcp"
    volumes:
      - ./hosts.conf:/hosts.conf:rw

You can use the docker volume to mount the hosts.conf file outside the container, which is convenient for you to modify.

Tips: Please note that if you use vim to edit, it may cause inode changes due to vim's backupcopy settings, which will make the compilation action incorrectly perceived. Set as below:

echo "set backupcopy=yes" >> ~/.vimrc

Serving A/AAAA records from a hosts file

The --hostsfile parameter expects a standard plain text hosts file with the only difference being that a wildcard * in the left-most label of hostnames is allowed. Wildcard entries will match any subdomain that is not explicitly defined. For example, given a hosts file with the following content:

192.168.0.1 db1.db.local
192.168.0.2 *.db.local

Queries for db2.db.local would be answered with an A record pointing to 192.168.0.2, while queries for db1.db.local would yield an A record pointing to 192.168.0.1.