System/Servenix: Add initial servenix system configuration

system/services/adguard.nix

@@ -0,0 +1,49 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}: {
+  virtualisation.oci-containers.containers.adguard = {
+    image = "adguard/adguardhome";
+    autoStart = true;
+
+    dependsOn = [];
+
+    ports = [
+      # DNS server
+      "53:53/tcp"
+      "53:53/udp"
+      # "853:853/tcp" # DNS over TLS
+      # "853:853/udp" # DNS over QUIC
+
+      # DHCP server
+      # "67:67/udp"
+      # "68:68/tcp"
+      # "68:68/udp"
+
+      # Admin panel + DNS over HTTPS
+      # "80:80/tcp"
+      # "443:443/tcp"
+      # "443:443/udp"
+      # "3100:3000/tcp" # Web interface
+
+      # DNSCrypt
+      # "5443:5443/tcp"
+      # "5443:5443/udp"
+
+      # "6060:6060/tcp" # Debugging
+    ];
+
+    volumes = [
+      "adguard_config:/opt/adguardhome/conf"
+      "adguard_work:/opt/adguardhome/work"
+    ];
+
+    environment = {};
+
+    extraOptions = [
+      "--net=behind-nginx"
+    ];
+  };
+}