Add 'dynrecord' verb.

README.md

@@ -43,20 +43,32 @@ Congrats! you now have a useless DNS zone with no records! You can add them with
 
 # Tool Usage
 
+if you're using a JSON keyfile as above, you don't need to specify ```--cloud-project``` if the project is named there.
+
+If you don't specify ```--json-keyfile``` then we'l try to use default credentials (i.e. the ones that the ```gcloud``` CLI uses). The examples below do this for clarity.
+
+## ```getzonefile``` and ```putzonefile``` - Zonefile Nonsense
+
 If you want to spit out a mostly valid zonefile from your gcloud-dns zone, this will do it:
 
-`clouddns-sync --json-keyfile=mykeyfile.json --cloud-project=mydnsproject --cloud-dns-zone=myzone getzonefile`
+`clouddns-sync --cloud-project=mydnsproject --cloud-dns-zone=myzone getzonefile`
 
 If you have a zonefile, slurp it into gcloud DNS by doing this: 
 
-`clouddns-sync --json-keyfile=mykeyfile.json --cloud-project=mydnsproject --cloud-dns-zone=myzone --zonefile=myzonefile putzonefile`
+`clouddns-sync --cloud-project=mydnsproject --cloud-dns-zone=myzone --zonefile=myzonefile putzonefile`
 
 You can add `--dry-run` to putzonefile to see what we'd do. You can also add `--prune-missing` to remove RRs that aren't in your zonefile but are in gcloud.
 
 My own use case is to do this once and then do future updates from a data source more reliable than your grandad's text file.
 
-# Update from Nomad cluster (EXPERIMENTAL)
+## ```nomad_sync``` Update from Nomad cluster 
 
 ```clouddns-sync --cloud-project=mydnsproject --cloud-dns-zone=myzone --nomad-server-uri=http://anynomadserver:4646/ nomad_sync```
 
 Right now we build a list of A records by inspecting all allocs and pointing *jobname*.domain to all nodes that hold an alloc in that job. That might not be what you want, but the important thing is that it's what I want. Patches welcome!
+
+## ```dynrecord``` dyndns-style single record updating
+
+This is if you have a DNS name you want to do 'dyndns' style updating for (i.e. we find out what our public IP is and set the specificed A record to that.)
+
+```clouddns-sync --cloud-project=mydnsproject --cloud-dns-zone=myzone --cloud-dns-dyn-record-name=myhomeip.domain.tld. dynrecord```

clouddns.go

@@ -373,3 +373,32 @@ func buildDnsChange(cloud_rrs, zone_rrs []*dns.ResourceRecordSet, prune_missing
 	return &ret
 
 }
+
+func updateOneARecord(dns_spec *CloudDNSSpec, record_name string, old_ip, new_ip string) error {
+
+	log.Printf("Updating Cloud DNS: %s : %s -> %s", record_name, old_ip, new_ip)
+
+	change := &dns.Change{
+		Additions: []*dns.ResourceRecordSet{
+			{
+				Name:    record_name,
+				Type:    "A",
+				Rrdatas: []string{new_ip},
+				Ttl:     int64(*dns_spec.default_ttl),
+			},
+		},
+	}
+
+	// Gcloud DNS shits the bed if you try to delete a record that's not there.
+	if old_ip != "" {
+		new_rr := dns.ResourceRecordSet{
+			Name:    record_name,
+			Type:    "A",
+			Rrdatas: []string{old_ip},
+			Ttl:     int64(*dns_spec.default_ttl),
+		}
+		change.Deletions = append(change.Deletions, &new_rr)
+	}
+
+	return processCloudDnsChange(dns_spec, change)
+}

main.go

@@ -3,7 +3,10 @@ package main
 import (
 	"context"
 	"flag"
+	"io"
 	"log"
+	"net"
+	"net/http"
 	"os"
 	"time"
 
@@ -21,20 +24,44 @@ type CloudDNSSpec struct {
 	dry_run     *bool
 }
 
+func getMyIP() (string, error) {
+	res, err := http.Get("http://whatismyip.akamai.com")
+	if err != nil {
+		log.Fatal("HTTP Error getting our IP: ", err)
+	}
+
+	resBody, err := io.ReadAll(res.Body)
+	if err != nil {
+		log.Fatal("Error reading response body: ", err)
+	}
+
+	ip := net.ParseIP(string(resBody))
+	if ip == nil {
+		log.Fatalf("Non-IP returned from request: %s", ip)
+	}
+
+	return string(resBody), nil
+}
+
 func main() {
-	var jsonKeyfile = flag.String("json-keyfile", "key.json", "json credentials file for Cloud DNS")
+	var jsonKeyfile = flag.String("json-keyfile", "", "json credentials file for Cloud DNS")
 	var cloudProject = flag.String("cloud-project", "", "Google Cloud Project")
 	var cloudZone = flag.String("cloud-dns-zone", "", "Cloud DNS zone to operate on")
 	var defaultCloudTtl = flag.Int("cloud-dns-default-ttl", 300, "Default TTL for Cloud DNS records")
-
-	var zoneFilename = flag.String("zonefilename", "", "Local zone file to operate on")
 	var dryRun = flag.Bool("dry-run", false, "Do not update Cloud DNS, print what would be done")
 	var pruneMissing = flag.Bool("prune-missing", false, "on putzonefile, prune cloud dns entries not in zone file")
 
+	// For [get|put]zonefile
+	var zoneFilename = flag.String("zonefilename", "", "Local zone file to operate on")
+
+	// for nomad_sync
 	var nomadServerURI = flag.String("nomad-server-uri", "http://localhost:4646", "URI for a nomad server to talk to.")
 	var nomadTokenFile = flag.String("nomad-token-file", "", "file to read ou rnomad token from")
 	var nomadSyncInterval = flag.Int("nomad-sync-interval-secs", 300, "seconds between nomad updates. set to -1 to sync once only.")
 
+	// for dynrecord
+	var cloudDnsDynRecordName = flag.String("cloud-dns-dyn-record-name", "", "Cloud DNS record to update with our IP")
+
 	flag.Parse()
 
 	// Verb and flag verification
@@ -44,10 +71,7 @@ func main() {
 
 	verb := flag.Args()[0]
 
-	// These are required in all cases
-	if *cloudProject == "" {
-		log.Fatal("--cloud-project is required")
-	}
+	// Required in all cases
 	if *cloudZone == "" {
 		log.Fatal("--cloud-dns-zone is required")
 	}
@@ -58,17 +82,32 @@ func main() {
 		}
 	}
 
-	jsonData, ioerror := os.ReadFile(*jsonKeyfile)
-	if ioerror != nil {
-		log.Fatal(*jsonKeyfile, ioerror)
+	if verb == "dynrecord" {
+		if *cloudDnsDynRecordName == "" {
+			log.Fatal("--cloud-dns-dyn-record-name is required for dynrecord")
+		}
 	}
 
 	ctx := context.Background()
+	creds := &google_oauth.Credentials{}
+
+	if *jsonKeyfile != "" {
+		jsonData, ioerror := os.ReadFile(*jsonKeyfile)
+		if ioerror != nil {
+			log.Fatal(*jsonKeyfile, ioerror)
+		}
+		creds, _ = google_oauth.CredentialsFromJSON(ctx, jsonData, "https://www.googleapis.com/auth/cloud-platform")
+	} else {
+		creds, _ = google_oauth.FindDefaultCredentials(ctx)
+	}
 
-	creds, err := google_oauth.CredentialsFromJSON(ctx, jsonData, "https://www.googleapis.com/auth/cloud-platform")
+	// Get project from json keyfile if present.
+	if creds.ProjectID != "" {
+		*cloudProject = creds.ProjectID
+	}
 
-	if err != nil {
-		log.Fatal("Cloud DNS Error: ", err)
+	if *cloudProject == "" {
+		log.Fatal("--cloud-project is required if not defined in json credentials")
 	}
 
 	dnsservice, err := dns.NewService(ctx, option.WithCredentials(creds))
@@ -89,13 +128,44 @@ func main() {
 		log.Fatal(err)
 	}
 
-	log.Print("Found zone in Cloud DNS")
-
 	switch verb {
 	case "getzonefile":
 		dumpZonefile(dns_spec)
 	case "putzonefile":
 		uploadZonefile(dns_spec, zoneFilename, dryRun, pruneMissing)
+	case "dynrecord":
+		my_ip, err := getMyIP()
+		if err != nil {
+			log.Fatalf("Error getting our IP: %s", err)
+		}
+
+		log.Printf("Detected IP: %s", my_ip)
+
+		current_dns, err := net.LookupIP(*cloudDnsDynRecordName)
+
+		current_ip := ""
+
+		if err != nil {
+			log.Print("Error in DNS resolution: ", err)
+			log.Print("Continuing...")
+		} else {
+			if len(current_dns) > 1 {
+				log.Fatalf("%s resolves to multiple IPs. Weird.", *cloudDnsDynRecordName)
+			}
+
+			current_ip = current_dns[0].To4().String()
+
+			if my_ip == current_ip {
+				log.Print("My IP matches DNS. Nothing to do.")
+				return
+			}
+		}
+
+		err = updateOneARecord(dns_spec, *cloudDnsDynRecordName, current_ip, my_ip)
+
+		if err != nil {
+			log.Fatalf("Error Updating GCloud: %s", err)
+		}
 	case "nomad_sync":
 		nomadSpec := &NomadSpec{
 			uri: *nomadServerURI,