ildkule: add config for prometheus_mysqld_exporter

There's a PR waiting to add this module to nixpkgs,
so we should enable this once it gets merged.

hosts/ildkule/services/metrics/grafana.nix

@@ -64,6 +64,13 @@ in {
           url = "https://raw.githubusercontent.com/matrix-org/synapse/develop/contrib/grafana/synapse.json";
           options.path = dashboards/synapse.json;
         }
+	# TODO: enable once https://github.com/NixOS/nixpkgs/pull/242365 gets merged
+	# {
+	#   name = "MySQL";
+	#   type = "file";
+	#   url = "https://raw.githubusercontent.com/prometheus/mysqld_exporter/main/mysqld-mixin/dashboards/mysql-overview.json";
+	#   options.path = dashboards/mysql.json;
+	# }
         {
           name = "Postgresql";
           type = "file";

hosts/ildkule/services/metrics/prometheus/default.nix

@@ -1,9 +1,11 @@
 { config, ... }: {
   imports = [
-    ./node.nix
-    ./matrix-synapse.nix
-    ./postgres.nix
     ./gogs.nix
+    ./matrix-synapse.nix
+    # TODO: enable once https://github.com/NixOS/nixpkgs/pull/242365 gets merged
+    # ./mysqld.nix
+    ./node.nix
+    ./postgres.nix
   ];
 
   services.prometheus = {

hosts/ildkule/services/metrics/prometheus/mysqld.nix

@@ -0,0 +1,25 @@
+{ config, unstable, ... }: let
+  cfg = config.services.prometheus;
+in {
+  sops.secrets."config/mysqld_exporter" = { };
+
+  services.prometheus = {
+    scrapeConfigs = [{
+      job_name = "mysql";
+      scheme = "http";
+      metrics_path = cfg.exporters.mysqld.telemetryPath;
+      static_configs = [
+        {
+          targets = [
+            "localhost:${toString cfg.exporters.mysqld.port}"
+          ];
+        }
+      ];
+    }];
+
+    exporters.mysqld = {
+      enable = true;
+      configFilePath = config.sops.secrets."config/mysqld_exporter".path;
+    };
+  };
+}