Add alert and dashboard using config file hashes

This allow to monitor the roll out of new config file versions to the
various nodes of a cluster. The metric was added as part of
cortexproject/cortex#2874.

Author: simonswine

cortex-mixin/alerts/alerts.libsonnet

@@ -91,6 +91,21 @@
             |||,
           },
         },
+        {
+          alert: 'CortexInconsistentConfig',
+          expr: |||
+            count(count by(%s, sha256) (cortex_config_hash)) without(sha256) > 1
+          ||| % $._config.alert_aggregation_labels,
+          'for': '1h',
+          labels: {
+            severity: 'warning',
+          },
+          annotations: {
+            message: |||
+              An inconsistent config file hash is used across cluster {{ $labels.job }}.
+            |||,
+          },
+        },
         {
           // As of https://github.com/cortexproject/cortex/pull/2092, this metric is
           // only exposed when it is supposed to be non-zero, so we don't need to do

cortex-mixin/dashboards.libsonnet

@@ -1,5 +1,6 @@
 {
   grafanaDashboards+:
+    (import 'dashboards/config.libsonnet') +
     (import 'dashboards/queries.libsonnet') +
     (import 'dashboards/reads.libsonnet') +
     (import 'dashboards/ruler.libsonnet') +

cortex-mixin/dashboards/config.libsonnet

@@ -0,0 +1,26 @@
+local utils = import 'mixin-utils/utils.libsonnet';
+
+(import 'dashboard-utils.libsonnet') {
+
+  'cortex-config.json':
+    $.dashboard('Cortex / Config')
+    .addClusterSelectorTemplates()
+    .addRow(
+      $.row('Startup config file')
+      .addPanel(
+        $.panel('Startup config file hashes') +
+        $.queryPanel('count(cortex_config_hash) by (sha256)', 'sha256:{{sha256}}') +
+        $.stack +
+        { yaxes: $.yaxes('instances') },
+      )
+    )
+    .addRow(
+      $.row('Runtime config file')
+      .addPanel(
+        $.panel('Runtime config file hashes') +
+        $.queryPanel('count(cortex_runtime_config_hash) by (sha256)', 'sha256:{{sha256}}') +
+        $.stack +
+        { yaxes: $.yaxes('instances') },
+      )
+    ),
+}