Add hourly request volume metric

This is pulled from Prometheus as well.

doc/development/telemetry/usage_ping.md

@@ -666,8 +666,9 @@ appear to be associated to any of the services running, since they all appear to
 | `clusters_applications_runner`                            | `usage_activity_by_stage`            | `verify`      |                  |         | Unique clusters with Runner enabled                                        |
 | `projects_reporting_ci_cd_back_to_github: 0`              | `usage_activity_by_stage`            | `verify`      |                  |         | Unique projects with a GitHub pipeline enabled                             |
 | `merge_requests_users`                                    | `usage_activity_by_stage_monthly`    | `create`      |                  |         | Unique count of users who used a merge request                             |
-| `nodes`                                                   | `topology`                           | `enablement`  |                  |         | The list of server nodes on which GitLab components are running            |
 | `duration_s`                                              | `topology`                           | `enablement`  |                  |         | Time it took to collect topology data                                      |
+| `application_requests_per_hour`                           | `topology`                           | `enablement`  |                  |         | Number of requests to the web application per hour                         |
+| `nodes`                                                   | `topology`                           | `enablement`  |                  |         | The list of server nodes on which GitLab components are running            |
 | `node_memory_total_bytes`                                 | `topology > nodes`                   | `enablement`  |                  |         | The total available memory of this node                                    |
 | `node_cpus`                                               | `topology > nodes`                   | `enablement`  |                  |         | The number of CPU cores of this node                                       |
 | `node_services`                                           | `topology > nodes`                   | `enablement`  |                  |         | The list of GitLab services running on this node                           |
@@ -873,6 +874,8 @@ The following is example content of the Usage Ping payload.
     }
   },
   "topology": {
+    "duration_s": 0.013836685999194742,
+    "application_requests_per_hour": 4224,
     "nodes": [
       {
         "node_memory_total_bytes": 33269903360,
@@ -897,8 +900,7 @@ The following is example content of the Usage Ping payload.
         ...
       },
       ...
-    ],
-    "duration_s": 0.013836685999194742
+    ]
   }
 }
 ```

lib/gitlab/usage_data_concerns/topology.rb

@@ -28,9 +28,18 @@ module Gitlab
       def topology_fetch_all_data
         with_prometheus_client(fallback: {}) do |client|
           {
+            application_requests_per_hour: topology_app_requests_per_hour(client),
             nodes: topology_node_data(client)
-          }
+          }.compact
+        end
       end
+
+      def topology_app_requests_per_hour(client)
+        result = client.query(one_week_average('gitlab_usage_ping:ops:rate5m')).first
+        return unless result
+
+        # the metric is recorded as a per-second rate
+        (result['value'].last.to_f * 1.hour).to_i
       end
 
       def topology_node_data(client)

spec/lib/gitlab/usage_data_concerns/topology_spec.rb

@@ -22,6 +22,7 @@ RSpec.describe Gitlab::UsageDataConcerns::Topology do
       context 'tracking node metrics' do
         it 'contains node level metrics for each instance' do
           expect_prometheus_api_to(
+            receive_app_request_volume_query,
             receive_node_memory_query,
             receive_node_cpu_count_query,
             receive_node_service_memory_rss_query,
@@ -32,6 +33,7 @@ RSpec.describe Gitlab::UsageDataConcerns::Topology do
 
           expect(subject[:topology]).to eq({
             duration_s: 0,
+            application_requests_per_hour: 36,
             nodes: [
               {
                 node_memory_total_bytes: 512,
@@ -76,6 +78,7 @@ RSpec.describe Gitlab::UsageDataConcerns::Topology do
       context 'and some node memory metrics are missing' do
         it 'removes the respective entries' do
           expect_prometheus_api_to(
+            receive_app_request_volume_query(result: []),
             receive_node_memory_query(result: []),
             receive_node_cpu_count_query,
             receive_node_service_memory_rss_query(result: []),
@@ -149,6 +152,17 @@ RSpec.describe Gitlab::UsageDataConcerns::Topology do
     end
   end
 
+  def receive_app_request_volume_query(result: nil)
+    receive(:query)
+      .with(/gitlab_usage_ping:ops:rate/)
+      .and_return(result || [
+        {
+          'metric' => { 'component' => 'http_requests', 'service' => 'workhorse' },
+          'value' => [1000, '0.01']
+        }
+      ])
+  end
+
   def receive_node_memory_query(result: nil)
     receive(:query)
       .with(/node_memory_total_bytes/, an_instance_of(Hash))