Allow adding aliases for subdomains

README.md

@@ -42,6 +42,6 @@ $ export TSDNS_DNSSERVER_PORT=2222
 
  - Webhook endpoint allowing automatic refreshing of devices when a new device is added
  - LetsEncrypt DNS-01 Challenge integration
- - Config based static records/aliases
+ - ~Config based static records/aliases~
  - Simple web ui listing status
  - Status url for Prometheus or monitoring

config.go

@@ -40,6 +40,7 @@ func loadConfig() {
 	viper.SetDefault("dns-server.port", 53)
 	viper.SetDefault("tailscale.hostname", "tailscale-custom-domain-dns")
 	viper.SetDefault("tailscale.ephemeral", false)
+	viper.SetDefault("aliases.subdomains", map[string]string{})
 
 	// Read the config
 	configFile, err := os.Open(configPath)

examples/tailscale-custom-domain-dns.toml

@@ -60,3 +60,7 @@ interval = "1h"
 # Alias for the root domain without any subdomain
 # Example: root = "machine-one"
 root = ""
+
+[aliases.subdomains]
+# Aliases for subdomains, they take the form of:
+# alias = "existing-device-name"

server/dns.go

@@ -120,10 +120,12 @@ func makeHandler(readDevices chan ReadDevicesOp, host string) DnsHandler {
 		// Get just the subdomain name from the request
 		name := strings.ReplaceAll(question.Name, "."+host, "")
 
+		// Get possible aliases
+		aliases := viper.GetStringMapString("aliases.subdomains")
+
 		var rrs []dns.RR
 		if question.Name == host {
 			// If the hostname is bare, check for a root alias
-
 			if viper.IsSet("aliases.root") {
 				name := viper.GetString("aliases.root")
 				if device, ok := deviceMap[name]; ok {
@@ -136,7 +138,22 @@ func makeHandler(readDevices chan ReadDevicesOp, host string) DnsHandler {
 					m.Answer = rrs
 				}
 			}
+		} else if alias, ok := aliases[name]; ok {
+			// Respond with an alias
+			if device, ok := deviceMap[alias]; ok {
+				log.
+					Debug().
+					Str("host", name).
+					Msgf(`Serving alias "%s" redirects to "%s"`, question.Name, alias)
+
+				rrs = constructResponses(name, device, question, host)
+				m.Answer = rrs
+			}
 		} else if device, ok := deviceMap[name]; ok {
+			log.
+				Debug().
+				Msgf(`Serving normal response "%s"`, question.Name)
+
 			// Respond if a device with the hostname exists
 			rrs = constructResponses(name, device, question, host)
 		}