metrics: introduce config status gauge

The approach used to represent enum metric here is similar to one
discussed in [1, 2]. It allows to support a new status later, if
required. For example, one can visualize it with hack like [3].

1. prometheus/client_python#416
2. open-telemetry/opentelemetry-specification#1711
3. https://stackoverflow.com/a/75761900/11646599

Part of tarantool/grafana-dashboard#224

Author: DifferentialOrange

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - New Tarantool 3 metrics:
   - tnt_config_alerts
+  - tnt_config_status
 
 ## [1.1.0] - 2024-05-17
 ### Added

doc/monitoring/metrics_reference.rst

@@ -1010,4 +1010,23 @@ These metrics are available starting from Tarantool 3.0.
             -   Count of current instance :ref:`configuration apply alerts <config_api_reference_info>`.
                 ``{level="warn"}`` label covers warnings and
                 ``{level="error"}`` covers errors.
+
+        *   -   ``tnt_config_status``
+            -   The status of current instance :ref:`configuration apply <config_api_reference_info>`.
+                ``status`` label contains possible status name.
+                Current status has metric value ``1``, inactive statuses have metric value ``0``.
+
+                ..  code-block:: none
+
+                    # HELP tnt_config_status Tarantool 3 configuration status
+                    # TYPE tnt_config_status gauge
+                    tnt_config_status{status="reload_in_progress",alias="router-001-a"} 0
+                    tnt_config_status{status="uninitialized",alias="router-001-a"} 0
+                    tnt_config_status{status="check_warnings",alias="router-001-a"} 0
+                    tnt_config_status{status="ready",alias="router-001-a"} 1
+                    tnt_config_status{status="check_errors",alias="router-001-a"} 0
+                    tnt_config_status{status="startup_in_progress",alias="router-001-a"} 0
+
+                For example, this set of metrics means that current configuration
+                for ``router-001-a`` status is ``ready``.
 

metrics/tarantool/config.lua

@@ -16,6 +16,23 @@ local function get_config_alerts(config_info)
     return config_alerts
 end
 
+local function get_config_status(config_info)
+    -- See state diagram here
+    -- https://github.com/tarantool/doc/issues/3544#issuecomment-1866033480
+    local config_status = {
+        uninitialized = 0,
+        startup_in_progress = 0,
+        reload_in_progress = 0,
+        check_warnings = 0,
+        check_errors = 0,
+        ready = 0,
+    }
+
+    config_status[config_info.status] = 1
+
+    return config_status
+end
+
 local function update()
     if not utils.is_tarantool3() then
         return
@@ -38,6 +55,19 @@ local function update()
             {default = true}
         )
     end
+
+    local config_status = get_config_status(config_info)
+
+    for status, value in pairs(config_status) do
+        collectors_list.config_status = utils.set_gauge(
+            'config_status',
+            'Tarantool 3 configuration status',
+            value,
+            {status = status},
+            nil,
+            {default = true}
+        )
+    end
 end
 
 return {

test/tarantool/config_metrics_test.lua

@@ -123,51 +123,122 @@ local function assert_config_alerts_metrics(server, expected_values)
     t.assert_equals(errors.value, expected_values['error'])
 end
 
+local function assert_config_status_metrics(server, expected_values)
+    local observations = server:exec(function()
+        local metrics = require('metrics')
+        metrics.invoke_callbacks()
+        return metrics.collect()
+    end)
 
-g.before_test('test_config_alerts_if_healthy', start_server)
-g.after_test('test_config_alerts_if_healthy', stop_server)
+    for status, expected_value in pairs(expected_values) do
+        local actual_obs = utils.find_obs(
+            'tnt_config_status',
+            {status = status, alias = 'server-001-a'},
+            observations
+        )
+        t.assert_equals(actual_obs.value, expected_value,
+                        ("got expected value for %q"):format(status))
+    end
+end
 
-g.test_config_alerts_if_healthy = function(cg)
+
+g.before_test('test_config_metrics_if_healthy', start_server)
+g.after_test('test_config_metrics_if_healthy', stop_server)
+
+g.test_config_metrics_if_healthy = function(cg)
     assert_config_alerts_metrics(cg.server, {warn = 0, error = 0})
+    assert_config_status_metrics(cg.server, {
+        uninitialized = 0,
+        startup_in_progress = 0,
+        reload_in_progress = 0,
+        check_warnings = 0,
+        check_errors = 0,
+        ready = 1,
+    })
 end
 
 
-g.before_test('test_config_alerts_if_minor_trouble', start_server)
-g.after_test('test_config_alerts_if_minor_trouble', stop_server)
+g.before_test('test_config_metrics_if_minor_trouble', start_server)
+g.after_test('test_config_metrics_if_minor_trouble', stop_server)
 
-g.test_config_alerts_if_minor_trouble = function(cg)
+g.test_config_metrics_if_minor_trouble = function(cg)
     local config = table.deepcopy(default_config)
     config['credentials']['users']['user_one'] = {roles = {'role_two'}}
     reload_config(cg, config)
 
     assert_config_alerts_metrics(cg.server, {warn = 1, error = 0})
+    assert_config_status_metrics(cg.server, {
+        uninitialized = 0,
+        startup_in_progress = 0,
+        reload_in_progress = 0,
+        check_warnings = 1,
+        check_errors = 0,
+        ready = 0,
+    })
 end
 
 
-g.before_test('test_config_alerts_if_critical_failure', start_server)
-g.after_test('test_config_alerts_if_critical_failure', stop_server)
+g.before_test('test_config_metrics_if_critical_failure', start_server)
+g.after_test('test_config_metrics_if_critical_failure', stop_server)
 
-g.test_config_alerts_if_critical_failure = function(cg)
+g.test_config_metrics_if_critical_failure = function(cg)
     local config = table.deepcopy(default_config)
     config['groups']['servers'] = {}
     reload_config(cg, config)
 
     assert_config_alerts_metrics(cg.server, {warn = 0, error = 1})
+    assert_config_status_metrics(cg.server, {
+        uninitialized = 0,
+        startup_in_progress = 0,
+        reload_in_progress = 0,
+        check_warnings = 0,
+        check_errors = 1,
+        ready = 0,
+    })
 end
 
 
-g.before_test('test_config_alerts_if_unsupported', function(cg)
+g.before_test('test_config_metrics_if_uninitialized', function(cg)
+    t.skip_if(not utils.is_tarantool_3_config_supported(),
+              'Skip since Tarantool 3 config is unsupported')
+    utils.create_server(cg)
+    cg.server:exec(function()
+        -- Config do it by default:
+        -- https://github.com/tarantool/tarantool/blob/319357d5973d15d08b8eda6a230eada08b710802/src/box/lua/config/applier/box_cfg.lua#L614
+        box.cfg{metrics = {labels = {alias = 'server-001-a'}}}
+    end)
+end)
+
+g.after_test('test_config_metrics_if_uninitialized', function(cg)
+    utils.drop_server(cg)
+    cg.server = nil
+end)
+
+g.test_config_metrics_if_uninitialized = function(cg)
+    assert_config_alerts_metrics(cg.server, {warn = 0, error = 0})
+    assert_config_status_metrics(cg.server, {
+        uninitialized = 1,
+        startup_in_progress = 0,
+        reload_in_progress = 0,
+        check_warnings = 0,
+        check_errors = 0,
+        ready = 0,
+    })
+end
+
+
+g.before_test('test_config_metrics_if_unsupported', function(cg)
     t.skip_if(utils.is_tarantool_3_config_supported(),
               'Skip since Tarantool 3 config is supported')
     utils.create_server(cg)
 end)
 
-g.after_test('test_config_alerts_if_unsupported', function(cg)
+g.after_test('test_config_metrics_if_unsupported', function(cg)
     utils.drop_server(cg)
     cg.server = nil
 end)
 
-g.test_config_alerts_if_unsupported = function(cg)
+g.test_config_metrics_if_unsupported = function(cg)
     local observations = cg.server:exec(function()
         local metrics = require('metrics')
         metrics.invoke_callbacks()
@@ -176,4 +247,7 @@ g.test_config_alerts_if_unsupported = function(cg)
 
     local alerts = utils.find_metric('tnt_config_alerts', observations)
     t.assert_equals(alerts, nil)
+
+    local status = utils.find_metric('tnt_config_status', observations)
+    t.assert_equals(status, nil)
 end