netdata: fix python plugins

(cherry picked from commit e08ee4971652b402888e2bc2ecec75a83ba661d8)

nixos/modules/services/monitoring/netdata.nix

@@ -53,6 +53,31 @@ in {
         '';
       };
 
+      python = {
+        enable = mkOption {
+          type = types.bool;
+          default = true;
+          description = ''
+            Whether to enable python-based plugins
+          '';
+        };
+        extraPackages = mkOption {
+          default = ps: [];
+          defaultText = "ps: []";
+          example = literalExample ''
+            ps: [
+              ps.psycopg2
+              ps.docker
+              ps.dnspython
+            ]
+          '';
+          description = ''
+            Extra python packages available at runtime
+            to enable additional python plugins.
+          '';
+        };
+      };
+
       config = mkOption {
         type = types.attrsOf types.attrs;
         default = {};
@@ -75,10 +100,11 @@ in {
         }
       ];
     systemd.services.netdata = {
-      path = with pkgs; [ gawk curl ];
       description = "Real time performance monitoring";
       after = [ "network.target" ];
       wantedBy = [ "multi-user.target" ];
+      path = (with pkgs; [ gawk curl ]) ++ lib.optional cfg.python.enable
+        (pkgs.python3.withPackages cfg.python.extraPackages);
       preStart = concatStringsSep "\n" (map (dir: ''
         mkdir -vp ${dir}
         chmod 750 ${dir}
@@ -89,6 +115,7 @@ in {
       serviceConfig = {
         User = cfg.user;
         Group = cfg.group;
+        Environment="PYTHONPATH=${pkgs.netdata}/libexec/netdata/python.d/python_modules";
         PermissionsStartOnly = true;
         ExecStart = "${pkgs.netdata}/bin/netdata -D -c ${configFile}";
         TimeoutStopSec = 60;