dashboard: add read only status panel

Add master/slave status panel to a cluster overview section.
tnt_read_only metric was introduced in 0.11.0.

Part of #133

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Vinyl index and bloom filter memory panels
 - Clock delta panel
 - Replication status panel and alert example
+- Read only status panel
 
 ### Changed
 - Rework "Tarantool memory memory miscellaneous" section to "Tarantool runtime overview"

dashboard/panels/cluster.libsonnet

@@ -392,7 +392,7 @@ local prometheus = grafana.prometheus;
     title=title,
     description=description,
     datasource=datasource,
-    panel_width=24,
+    panel_width=12,
     max=1,
     min=0,
   ).addValueMapping(
@@ -417,6 +417,43 @@ local prometheus = grafana.prometheus;
       .selectField('value').addConverter('last')
   ),
 
+  read_only_status(
+    title='Tarantool instance status',
+    description=|||
+      `master` status means instance is available for read and
+      write operations. `slave` status means instance is
+      available only for read operations.
+
+      Panel works with `metrics >= 0.11.0` and Grafana 8.x.
+    |||,
+    datasource=null,
+    policy=null,
+    measurement=null,
+    job=null,
+  ):: timeseries.new(
+    title=title,
+    description=description,
+    datasource=datasource,
+    panel_width=12,
+    max=1,
+    min=0,
+  ).addValueMapping(
+    0, 'green', 'master'
+  ).addValueMapping(
+    1, 'yellow', 'slave'
+  ).addRangeMapping(
+    0.001, 0.999, '-'
+  ).addTarget(
+    common.default_metric_target(
+      datasource,
+      'tnt_read_only',
+      job,
+      policy,
+      measurement,
+      'last'
+    )
+  ),
+
   replication_lag(
     title='Tarantool replication lag',
     description=|||

dashboard/section.libsonnet

@@ -31,6 +31,12 @@ local vinyl = import 'panels/vinyl.libsonnet';
       measurement=measurement,
     ),
 
+    cluster.read_only_status(
+      datasource=datasource,
+      policy=policy,
+      measurement=measurement,
+    ),
+
     cluster.replication_lag(
       datasource=datasource,
       policy=policy,
@@ -101,6 +107,11 @@ local vinyl = import 'panels/vinyl.libsonnet';
       job=job,
     ),
 
+    cluster.read_only_status(
+      datasource=datasource,
+      job=job,
+    ),
+
     cluster.replication_lag(
       datasource=datasource,
       job=job,