Move rules to dedicated file

hosts/monitoring-3/configuration.nix

@@ -161,19 +161,7 @@ in {
         } ];
       }
     ];
-    rules = [ ''
-      groups:
-      - name: alert.rules
-        rules:
-        - alert: InstanceDown
-          expr: up == 0
-          for: 1m
-          labels:
-            severity: critical
-          annotations:
-            summary: "Endpoint {{ $labels.instance }} down"
-            description: "{{ $labels.instance }} of job {{ $labels.job }} has been down for more than 1 minutes."
-    '' ];
+    rules = [ (readFile ./rules.yml) ];
   };
 
   services.grafana = {

hosts/monitoring-3/rules.yml

@@ -0,0 +1,11 @@
+groups:
+- name: alert.rules
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+    for: 1m
+    labels:
+      severity: critical
+    annotations:
+      summary: "Endpoint {{ $labels.instance }} down"
+      description: "{{ $labels.instance }} of job {{ $labels.job }} has been down for more than 1 minutes."