From 81964183e8364b4ac9c4c0778741d668908fd518 Mon Sep 17 00:00:00 2001
From: pavel <pavel.larkin@ikeja.co.za>
Date: Wed, 8 Apr 2026 13:47:31 +0300
Subject: [PATCH] 1347

---
 files/nats_registration_listener.py | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/files/nats_registration_listener.py b/files/nats_registration_listener.py
index f2f0852..2bd37e4 100644
--- a/files/nats_registration_listener.py
+++ b/files/nats_registration_listener.py
@@ -125,6 +125,10 @@ NB_PROBLEM_LOCK = asyncio.Lock()
 # Structured event log output (JSON Lines)
 EVENT_LOG_PATH = os.environ.get("EVENT_LOG_PATH", "/opt/containers/nats-registration-listener/logs/registration_events.jsonl")
 
+EVENODD = (os.environ.get("EVENODD", "") or "").strip().lower()
+if EVENODD not in ("", "even", "odd"):
+    raise SystemExit("ERROR: EVENODD must be unset, 'even', or 'odd'")
+
 
 # =========================
 # Arg parsing
@@ -296,6 +300,18 @@ def normalize_mac(mac: str) -> Optional[str]:
     return None
 
 
+def mac_belongs_to_this_shard(mac_norm: Optional[str]) -> bool:
+    if EVENODD == "":
+        return True
+    if not mac_norm:
+        return True
+    md5_hex = hashlib.md5(mac_norm.encode("utf-8")).hexdigest()
+    last_nibble = int(md5_hex[-1], 16)
+    if EVENODD == "even":
+        return (last_nibble % 2) == 0
+    return (last_nibble % 2) == 1
+
+
 IGNORE_MACS = {m for m in (normalize_mac(x) for x in IGNORE_MACS_RAW) if m}
 
 
@@ -584,11 +600,11 @@ async def main():
                     recent_payloads.pop(k, None)
 
         product = mac = fw = "-"
+        obj = None
         try:
             text = payload.decode("utf-8", errors="replace")
             obj = json.loads(text)
             product, mac, fw = extract_fields(obj)
-            event["reg_age_s"] = extract_registration_age_s(obj)
         except Exception:
             pass
 
@@ -597,7 +613,15 @@ async def main():
         event["fw"] = fw
 
         mac_norm = normalize_mac(mac)
+        if not mac_belongs_to_this_shard(mac_norm):
+            return
+
         event["mac_norm"] = mac_norm
+        if obj is not None:
+            try:
+                event["reg_age_s"] = extract_registration_age_s(obj)
+            except Exception:
+                pass
         if mac_norm in IGNORE_MACS:
             event["ignored"] = True
             event["ignore_reason"] = "mac_ignore_list"