Statistics about amount of clusters configured

GitLab should reports about setup used for Gitaly.
Usual Gitaly setup with multiple storages will report
none clusters used, but setup with Praefect with
multiple Gitalies behind will report amount of such
Praefects as clusters.

Related to: https://gitlab.com/gitlab-org/gitaly/-/issues/2664

doc/development/telemetry/usage_ping.md

@@ -612,6 +612,7 @@ The following is example content of the Usage Ping payload.
   "gitaly": {
     "version": "12.10.0-rc1-93-g40980d40",
     "servers": 56,
+    "clusters": 14,
     "filesystems": [
       "EXT_2_3_4"
     ]

lib/gitaly/server.rb

@@ -3,6 +3,7 @@
 module Gitaly
   class Server
     SHA_VERSION_REGEX = /\A\d+\.\d+\.\d+-\d+-g([a-f0-9]{8})\z/.freeze
+    DEFAULT_REPLICATION_FACTOR = 1
 
     class << self
       def all
@@ -16,6 +17,10 @@ module Gitaly
       def filesystems
         all.map(&:filesystem_type).compact.uniq
       end
+
+      def gitaly_clusters
+        all.count { |g| g.replication_factor > DEFAULT_REPLICATION_FACTOR }
+      end
     end
 
     attr_reader :storage
@@ -73,6 +78,10 @@ module Gitaly
       "Error getting the address: #{e.message}"
     end
 
+    def replication_factor
+      storage_status&.replication_factor
+    end
+
     private
 
     def storage_status

lib/gitlab/usage_data.rb

@@ -217,6 +217,7 @@ module Gitlab
           gitaly: {
             version: alt_usage_data { Gitaly::Server.all.first.server_version },
             servers: alt_usage_data { Gitaly::Server.count },
+            clusters: alt_usage_data { Gitaly::Server.gitaly_clusters },
             filesystems: alt_usage_data(fallback: ["-1"]) { Gitaly::Server.filesystems }
           },
           gitlab_pages: {

spec/lib/gitaly/server_spec.rb

@@ -20,6 +20,7 @@ describe Gitaly::Server do
   it { is_expected.to respond_to(:git_binary_version) }
   it { is_expected.to respond_to(:up_to_date?) }
   it { is_expected.to respond_to(:address) }
+  it { is_expected.to respond_to(:replication_factor) }
 
   describe 'readable?' do
     context 'when the storage is readable' do
@@ -134,4 +135,22 @@ describe Gitaly::Server do
       end
     end
   end
+
+  describe 'replication_factor' do
+    context 'when examining for a given server' do
+      let(:storage_status) { double('storage_status', storage_name: 'default') }
+
+      before do
+        response = double('response', storage_statuses: [storage_status])
+        allow_next_instance_of(Gitlab::GitalyClient::ServerService) do |instance|
+          allow(instance).to receive(:info).and_return(response)
+        end
+      end
+
+      it do
+        allow(storage_status).to receive(:replication_factor).and_return(2)
+        expect(server.replication_factor).to eq(2)
+      end
+    end
+  end
 end

spec/lib/gitlab/usage_data_spec.rb

@@ -255,6 +255,7 @@ describe Gitlab::UsageData, :aggregate_failures do
           expect(subject[:database][:version]).to eq(Gitlab::Database.version)
           expect(subject[:gitaly][:version]).to be_present
           expect(subject[:gitaly][:servers]).to be >= 1
+          expect(subject[:gitaly][:clusters]).to be >= 0
           expect(subject[:gitaly][:filesystems]).to be_an(Array)
           expect(subject[:gitaly][:filesystems].first).to be_a(String)
         end