Update DNS repeatedly

Makefile

@@ -2,6 +2,7 @@ install:
 	cp hetzner-ddns.py /usr/local/bin
 	cp etc/hetzner-ddns.conf.example /etc
 	cp etc/systemd/hetzner-ddns.service /etc/systemd/system/
+	systemctl daemon-reload
 
 uninstall:
 	rm /usr/local/bin/hetzner-ddns.py

etc/systemd/hetzner-ddns.service

@@ -4,8 +4,8 @@ After=network-online.target
 Wants=network-online.target
 
 [Service]
-Type=oneshot
-ExecStart=/usr/local/bin/hetzner-ddns.py
+Type=simple
+ExecStart=python3 -u /usr/local/bin/hetzner-ddns.py
 
 [Install]
 WantedBy=multi-user.target

hetzner-ddns.py

@@ -20,6 +20,7 @@ Options:
   --config=<file>       Read options from configuration file
   --disable-v4          Do not update IPv4 address
   --disable-v6          Do not update IPv6 address
+  --repeat=<s>          Update DNS again every S seconds
 """
 
 from docopt import docopt
@@ -30,6 +31,7 @@ import requests
 import socket
 import sys
 import configparser
+import time
 
 
 args = docopt(__doc__)
@@ -75,6 +77,7 @@ def merge_defaults():
         "--retry-attempts": 12,
         "--retry-delay": 5,
         "--hostname": socket.gethostname(),
+        "--repeat": 3600,
     }
 
     print("Applying default options:")
@@ -171,8 +174,20 @@ def create_record(record):
     response.raise_for_status()
 
 
+def delete_record(rid):
+    response = requests.delete(
+        url=f"https://dns.hetzner.com/api/v1/records/{rid}",
+        headers={
+            "Content-Type": "application/json",
+            "Auth-API-Token": args["--token"],
+        }
+    )
+    response.raise_for_status()
+
+
 def main():
     kinds = []
+    delay = int(args["--repeat"])
 
     if not bool(args["--disable-v4"]):
         kinds += ["A"]
@@ -183,6 +198,7 @@ def main():
     print("Finding DNS zone...")
     zone = find_zone(args["--zone"])
 
+    while True:
         for kind in kinds:
             if kind == "A":
                 print("Finding public IPv4 address...")
@@ -196,8 +212,15 @@ def main():
             print("Finding existing %s record..." % kind)
             rec = find_record(zone=zone, kind=kind, name=args["--hostname"])
 
-        if rec is None:
-            print("    not found")
+            if rec is not None:
+                if rec["value"] == addr:
+                    print("Existing record is up-to-date")
+                    continue
+
+                print("Deleting existing %s record..." % kind)
+                delete_record(rec["id"])
+                print("    done")
+
             print("Creating new %s record..." % kind)
             create_record(
                 {
@@ -209,13 +232,8 @@ def main():
                 }
             )
             print("    done")
-        else:
-            print("    found")
-            print("Updating existing %s record..." % kind)
-            rec["value"] = addr
-            rec["ttl"] = args["--ttl"]
-            update_record(rec)
-            print("    done")
 
+        print(f"Sleeping for {delay} seconds...")
+        time.sleep(delay)
 
 main()