parallelizing domain checking

cmd/dnsupdater/main.go

@@ -3,11 +3,13 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"os"
 	"path"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/rs/zerolog"
@@ -107,39 +109,73 @@ func update(ctx context.Context, requester outboundip.IpRequester, manager dns.M
 	}
 	newIp := newIpResult.Ip
 
+	wg := sync.WaitGroup{}
+
 	updatedDomains := ""
+	updatedDomainsChannel := make(chan string)
 	for _, domain := range configuration.Domains {
-		currentIp, err := manager.GetARecord(domain)
-		if err != nil {
-			return fmt.Errorf("getting current ip: %v", err)
-		}
-
-		if currentIp == newIp {
-			continue
-		}
-		log.
-			Ctx(ctx).
-			Info().
-			Str("domain", domain).
-			Str("current ip", currentIp).
-			Str("new ip", newIp).
-			Msg("ip has changed")
-		err = manager.SetARecord(domain, newIp)
-		if err != nil {
-			return fmt.Errorf("setting current ip: %v", err)
-		}
-		updatedDomains += fmt.Sprintf("\t- %s\n", domain)
+		domain := domain
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			updated, err := checkDomain(manager, domain, newIp)
+			if err != nil {
+				log.Error().Err(err).Str("domain", domain).Msg("checking domain ip change")
+			}
+			if updated {
+				updatedDomainsChannel <- domain
+			}
+		}()
+	}
+	go func() {
+		wg.Wait()
+		close(updatedDomainsChannel)
+	}()
+	for {
+		select {
+		case <-ctx.Done():
+			return errors.New("context canceled")
+		case d, ok := <-updatedDomainsChannel:
+			if !ok {
+				updatedDomainsChannel = nil
+				break
+			}
+			updatedDomains += fmt.Sprintf("\t- %s\n", d)
+		}
+		if updatedDomainsChannel == nil {
+			break
+		}
 	}
-
 	if updatedDomains != "" {
 		SendStatusMail(fmt.Sprintf(`Home IP has changed : %s
 Dns updated successfully for domains
 %s`, newIp, updatedDomains))
 	}
-
 	return nil
 }
 
+func checkDomain(manager dns.Manager, domainname string, outboundip string) (bool, error) {
+	currentIp, err := manager.GetARecord(domainname)
+	if err != nil {
+		return false, fmt.Errorf("getting current ip: %v", err)
+	}
+
+	if currentIp == outboundip {
+		return false, nil
+	}
+	log.
+		Info().
+		Str("domain", domainname).
+		Str("current ip", currentIp).
+		Str("new ip", outboundip).
+		Msg("ip has changed")
+	err = manager.SetARecord(domainname, outboundip)
+	if err != nil {
+		return false, fmt.Errorf("setting current ip: %v", err)
+	}
+	return true, nil
+}
+
 func SendStatusMail(messageText string) {
 
 	settings := configuration.MailSettings