Adding alerting rules

docker/prometheus/etc/alert.rules

@@ -0,0 +1,22 @@
+groups:
+- name: example
+  rules:
+
+  # Alert for any instance that is unreachable for >2 minutes.
+  - alert: service_down
+    expr: up == 0
+    for: 2m
+    labels:
+      severity: page
+    annotations:
+      summary: "Instance {{ $labels.instance }} down"
+      description: "{{ $labels.instance }} of job {{ $labels.job }} has been down for more than 2 minutes."
+
+  - alert: high_load
+    expr: node_load1 > 0.5
+    for: 2m
+    labels:
+      severity: page
+    annotations:
+      summary: "Instance {{ $labels.instance }} under high load"
+      description: "{{ $labels.instance }} of job {{ $labels.job }} is under high load."