Enable metrics for matrix-synapse

config/hosts/metrics/prometheus.nix

@@ -1,8 +1,16 @@
-{ hosts, ... }:
+{ hosts, pkgs, ... }:
+let
+  # https://github.com/element-hq/synapse/tree/master/contrib/prometheus/
+  synapseRules = pkgs.fetchurl {
+    url = "https://raw.githubusercontent.com/element-hq/synapse/refs/heads/master/contrib/prometheus/synapse-v2.rules";
+    hash = "sha256-WldlBdCMzul49OlFhJMsrx4MYFakHTa36Y9HnV22EwI=";
+  };
+in
 {
   services.prometheus = {
     enable = true;
     retentionTime = "90d";
+    ruleFiles = [ synapseRules ];
     scrapeConfigs = [
       {
         job_name = "node";
@@ -15,6 +23,14 @@
           };
         }) (builtins.attrNames hosts);
       }
+      {
+        job_name = "synapse";
+        scrape_interval = "15s";
+        metrics_path = "/_synapse/metrics";
+        static_configs = [{
+          targets = [ "matrix.vs.grzb.de:9000" ];
+        }];
+      }
     ];
   };
 }