grafana-agent: make bagel.monitoring.grafana-agent.exporters an attrset

This allows us to use multiple jobs, one for each additional exporter,
and set their `job_name` accordingly.

`job_name` is exported as `job` label on the resulting metrics.
This allows us to quickly get an understanding what metrics of an
exporter are actually available by simply filtering all metrics by
`{job="$jobname"}`

services/monitoring/agent.nix

@@ -13,14 +13,20 @@ in
     enable = (mkEnableOption "Grafana Agent") // { default = true; };
 
     exporters = mkOption {
-      description = "List of all exporters to scrape";
-      type = types.listOf (types.submodule {
+      description = ''
+        Set of additional exporters to scrape.
+
+        The attribute name will be used as `job_name`
+        internally, which ends up exported as `job` label
+        on all metrics of that exporter.
+      '';
+      type = types.attrsOf (types.submodule {
         options.port = mkOption {
           description = "Exporter port";
           type = types.int;
         };
       });
-      default = [];
+      default = {};
     };
   };
 
@@ -45,14 +51,12 @@ in
           configs = [
             {
               name = config.networking.hostName;
-              scrape_configs = [
-                {
-                  job_name = config.networking.hostName;
+              scrape_configs = lib.mapAttrsToList (name: value: {
+                job_name = name;
                 static_configs = [
-                    { targets = map (e: "localhost:" + (toString e.port)) config.bagel.monitoring.grafana-agent.exporters; }
-                  ];
-                }
+                  { targets = "localhost:" + (toString value.port); }
                 ];
+              }) config.bagel.monitoring.grafana-agent.exporters;
             }
           ];
         };

services/monitoring/exporters/cadvisor.nix

@@ -17,6 +17,6 @@ in
       listenAddress = "0.0.0.0";
     };
 
-    bagel.monitoring.grafana-agent.exporters = [ { port = 9102; } ];
+    bagel.monitoring.grafana-agent.exporters.cadvisor.port = 9102;
   };
 }

services/monitoring/exporters/nginx.nix

@@ -30,8 +30,6 @@ in
       ];
     };
 
-    bagel.monitoring.grafana-agent.exporters = [
-      { port = 9103; }
-    ];
+    bagel.monitoring.grafana-agent.exporters.nginxlog.port = 9103;
   };
 }

services/monitoring/exporters/postgres.nix

@@ -24,8 +24,6 @@ in
 
     services.postgresql.settings.shared_preload_libraries = "pg_stat_statements";
 
-    bagel.monitoring.grafana-agent.exporters = [
-      { port = 9104; }
-    ];
+    bagel.monitoring.grafana-agent.exporters.postgres.port = 9104;
   };
 }