feat: add prometheus templates for easy alerting setup

docs/changelog.rst

@@ -2,6 +2,7 @@ CHANGELOG
 =====================================
 
 | January 17, 2021 : fix: `required-status-check` bug in merge action
+| January 15, 2021 : feat: add prometheus templates for easy alerting setup
 | January 14, 2021 : fix: validators not running in certain pull_request events `#431 <https://github.com/mergeability/mergeable/issues/431>`_
 | January 14, 2021 : fix: remove unsupported settings from title, description and milestone validator
 | January 14, 2021 : feat: Allow to have pending checks `#454 <https://github.com/mergeability/mergeable/issues/454>`_

helm/mergeable/templates/prometheus-rules.yaml

@@ -0,0 +1,13 @@
+{{- if .Values.prometheus.enabled }}
+apiVersion: monitoring.coreos.com/v1
+kind: PrometheusRule
+metadata:
+  name: {{ include "mergeable.fullname" . }}
+  labels:
+    {{- include "mergeable.labels" . | nindent 4 }}
+    prometheus: kube-prometheus
+    role: alert-rules
+spec:
+  groups:
+{{ toYaml .Values.prometheus.rules | nindent 4 }}
+{{- end }}

helm/mergeable/values.yaml

@@ -84,3 +84,19 @@ nodeSelector: {}
 tolerations: []
 
 affinity: {}
+
+prometheus:
+  enabled: false
+  rules: {}
+    # - name: mergeable
+    #   rules:
+    #   - alert: mergeable-ErrorRateTooHigh-Warning
+    #     expr: sum(rate(nginx_ingress_controller_requests{ingress="mergeable",status=~"5.{2}|4[1-9].|40[^14]"}[1m])) / sum(rate(nginx_ingress_controller_requests{ingress="mergeable"}[1m])) > 0.01
+    #     for: 10m
+    #     labels:
+    #       slack: $channel
+    #       severity: warning
+    #     annotations:
+    #       summary: Mergeable error rate greater than 1% in the last 10m
+    #       description: Mergeable has an HTTP error response rate of {{ $value }}% in the last 10m
+