Add "randomize" setting for controlling whether or not the "nameservers" list gets randomized on lookups

Author: tianon

cmd/rawdns/forwarding.go

@@ -15,7 +15,7 @@ import (
 	"github.com/miekg/dns"
 )
 
-func handleForwardingRaw(nameservers []string, req *dns.Msg, remote net.Addr) *dns.Msg {
+func handleForwardingRaw(nameservers []string, randomize bool, req *dns.Msg, remote net.Addr) *dns.Msg {
 	if len(nameservers) == 0 {
 		log.Printf("no nameservers defined, can not forward\n")
 		m := new(dns.Msg)
@@ -31,13 +31,17 @@ func handleForwardingRaw(nameservers []string, req *dns.Msg, remote net.Addr) *d
 		tcp = true
 	}
 
+	nsid := 0
+	if randomize {
+		// Use request Id for "random" nameserver selection.
+		nsid = int(req.Id) % len(nameservers)
+	}
+
 	var (
 		r   *dns.Msg
 		err error
 		try int
 	)
-	// Use request Id for "random" nameserver selection.
-	nsid := int(req.Id) % len(nameservers)
 	dnsClient := &dns.Client{Net: "udp", Timeout: 4 * time.Second, SingleInflight: true}
 	if tcp {
 		dnsClient.Net = "tcp"
@@ -68,6 +72,6 @@ Redo:
 }
 
 // ServeDNSForward forwards a request to a nameservers and returns the response.
-func handleForwarding(nameservers []string, w dns.ResponseWriter, req *dns.Msg) {
-	w.WriteMsg(handleForwardingRaw(nameservers, req, w.RemoteAddr()))
+func handleForwarding(nameservers []string, randomize bool, w dns.ResponseWriter, req *dns.Msg) {
+	w.WriteMsg(handleForwardingRaw(nameservers, randomize, req, w.RemoteAddr()))
 }

cmd/rawdns/main.go

@@ -35,6 +35,7 @@ type DomainConfig struct {
 
 	// "type": "forwarding"
 	Nameservers []string `json:"nameservers"` // [ "8.8.8.8", "8.8.4.4" ]
+	Randomize   *bool    `json:"randomize"`   // whether to randomize recursive lookups to spread upstream load (defaults to true)
 
 	// "type": "static"
 	Addrs  []string          `json:"addrs"`
@@ -74,6 +75,13 @@ func main() {
 	}
 
 	for domain := range config {
+		if config[domain].Randomize == nil {
+			domainConfig := config[domain]
+			randomize := true
+			domainConfig.Randomize = &randomize
+			config[domain] = domainConfig
+		}
+
 		switch config[domain].Type {
 		case "containers":
 			// TODO there must be a better way to pass "domain" along without an anonymous function AND copied variable
@@ -93,8 +101,9 @@ func main() {
 		case "forwarding":
 			// TODO there must be a better way to pass "domain" along without an anonymous function AND copied variable
 			nameservers := config[domain].Nameservers
+			randomize := *config[domain].Randomize
 			dns.HandleFunc(domain, func(w dns.ResponseWriter, r *dns.Msg) {
-				handleForwarding(nameservers, w, r)
+				handleForwarding(nameservers, randomize, w, r)
 			})
 		case "static":
 			cCopy := config[domain]
@@ -252,7 +261,7 @@ func handleStaticRequest(config DomainConfig, w dns.ResponseWriter, r *dns.Msg)
 					},
 					Question: []dns.Question{recQ},
 				}
-				recM := handleForwardingRaw(config.Nameservers, recR, w.RemoteAddr())
+				recM := handleForwardingRaw(config.Nameservers, *config.Randomize, recR, w.RemoteAddr())
 				for _, rr := range recM.Answer {
 					dnsAppend(recQ, m, rr)
 				}