Add election_leader_idle metric (#475)

CHANGELOG.md

@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   (`metrics.cfg{include={'all'}}` can be used instead of `metrics.cfg{include='all'}`,
   `metrics.cfg{exclude={'all'}}` can be used instead of `metrics.cfg{include='none'}`)
 
+- `tnt_election_leader_idle` metric.
+
 ## [1.0.0] - 2023-05-22
 ### Changed
 

doc/monitoring/metrics_reference.rst

@@ -773,6 +773,9 @@ Shows the current state of a replica set node in regards to leader election.
         *   -   ``tnt_election_term``
             -   Current election term.
 
+        *   -   ``tnt_election_leader_idle``
+            -   Time in seconds since the last interaction with the known leader.
+
 Memtx
 -----
 

metrics/tarantool/info.lua

@@ -91,6 +91,12 @@ local function update_info_metrics()
         collectors_list.election_term =
             utils.set_gauge('election_term', 'Current election term',
                 info.election.term, nil, nil, {default = true})
+
+        if info.election.leader_idle ~= nil then
+            collectors_list.election_leader_idle =
+                utils.set_gauge('election_leader_idle', 'Current idle for elected leader',
+                    info.election.leader_idle, nil, nil, {default = true})
+        end
     end
 end
 

test/tarantool/info_metrics_test.lua

@@ -93,3 +93,26 @@ g.test_election = function(cg)
         t.assert_type(tnt_election_term[1].value, 'number')
     end)
 end
+
+g.test_election_leader_idle = function(cg)
+    t.skip_if(utils.is_version_less(_TARANTOOL, '2.10.0'),
+        'Tarantool version is must be v2.10.0 or greater')
+
+    cg.server:exec(function()
+        box.cfg{election_mode = 'candidate'}
+        local metrics = require('metrics')
+        local info = require('metrics.tarantool.info')
+        local utils = require('test.utils') -- luacheck: ignore 431
+
+        metrics.enable_default_metrics()
+        info.update()
+        local default_metrics = metrics.collect()
+
+        local tnt_election_leader_idle = utils.find_metric(
+            'tnt_election_leader_idle', default_metrics
+        )
+        t.assert(tnt_election_leader_idle)
+        t.assert_type(tnt_election_leader_idle[1].value, 'number')
+        box.cfg{election_mode = 'off'}
+    end)
+end