Infra: Added robust DuckDNS updater and DNS monitoring sidecar container

dns-monitor/monitor.sh

@@ -0,0 +1,44 @@
+#!/bin/sh
+
+# Install curl and ping if not present (Alpine)
+if ! command -v curl >/dev/null 2>&1; then
+    apk add --no-cache curl
+fi
+
+echo "[DNS-MONITOR] Service started. Monitoring $SUBDOMAINS every 5 minutes..."
+
+while true; do
+    # Fetch Public IP
+    PUBLIC_IP=$(curl -s -m 10 https://api.ipify.org)
+    
+    if [ -z "$PUBLIC_IP" ]; then
+        PUBLIC_IP="Error: Could not fetch IP"
+    fi
+
+    # Get the first subdomain to check
+    FIRST_SUB=$(echo $SUBDOMAINS | cut -d',' -f1)
+    
+    if [ -z "$FIRST_SUB" ]; then
+        echo "[DNS-MONITOR] No subdomain found in env var SUBDOMAINS"
+    else
+        FULL_DOMAIN="${FIRST_SUB}.duckdns.org"
+
+        # Resolve IP using ping
+        DOMAIN_IP=$(ping -c 1 -W 5 "$FULL_DOMAIN" 2>/dev/null | head -n 1 | grep -oE '([0-9]{1,3}\.){3}[0-9]{1,3}' | head -n 1)
+
+        if [ -z "$DOMAIN_IP" ]; then
+             DOMAIN_IP="Error: Could not resolve"
+        fi
+
+        TIMESTAMP=$(date '+%Y-%m-%d %H:%M:%S')
+
+        if [ "$PUBLIC_IP" == "$DOMAIN_IP" ]; then
+            echo "[$TIMESTAMP] [DNS-MONITOR] OK | Domain: $FULL_DOMAIN ($DOMAIN_IP) == Public: $PUBLIC_IP"
+        else
+            echo "[$TIMESTAMP] [DNS-MONITOR] ALERT | Domain: $FULL_DOMAIN ($DOMAIN_IP) != Public: $PUBLIC_IP"
+        fi
+    fi
+
+    # Check every 5 minutes
+    sleep 300
+done