Add RemoteMirrorsProber

Related to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5313

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-monitor (3.5.0)
+    gitlab-monitor (3.6.0)
       connection_pool (~> 2.2.1)
       pg (~> 1.1)
       quantile (~> 0.2.0)

README.md

@@ -27,6 +27,8 @@ metrics.
     * [Bloat](lib/gitlab_monitor/database/bloat.rb) --
       `gitlab_database_bloat_$type_$key` with type `btree` (index bloat) or `table`
       (table bloat) and keys `bloat_ratio bloat_size extra_size real_size` (see below)
+    * [Remote mirrors](lib/gitlab_monitor/database/remote_mirrors.rb) --
+      `project_remote_mirror_last_successful_update_time_seconds`
 1. Git
     * [git pull/push timings](lib/gitlab_monitor/git.rb) --
       `git_pull_time_milliseconds`, `git_push_time_milliseconds`

config/gitlab-monitor.yml.example

@@ -60,6 +60,13 @@ probes:
         - soft_deleted_projects
         - orphaned_projects
         - uploads
+    remote_mirrors:
+      class_name: Database::RemoteMirrors
+      <<: *db_common
+      opts:
+        <<: *db_common_opts
+        project_ids:
+        - 1
 
   process: &process
     methods:

lib/gitlab_monitor/database.rb

@@ -7,6 +7,7 @@ module GitLab
       autoload :TuplesProber,         "gitlab_monitor/database/tuple_stats"
       autoload :RowCountProber,       "gitlab_monitor/database/row_count"
       autoload :BloatProber,          "gitlab_monitor/database/bloat"
+      autoload :RemoteMirrorsProber,  "gitlab_monitor/database/remote_mirrors"
     end
   end
 end

lib/gitlab_monitor/database/remote_mirrors.rb

+module GitLab
+  module Monitor
+    module Database
+      # A helper class to collect remote mirrors metrics.
+      class RemoteMirrorsCollector < Base
+        QUERY = <<~SQL.freeze
+          SELECT project_id, url, EXTRACT(EPOCH FROM last_successful_update_at) AS last_successful_update_at
+          FROM remote_mirrors WHERE project_id IN (%s) AND enabled = 't'
+        SQL
+
+        def initialize(args)
+          super(args)
+
+          @project_ids = args[:project_ids]
+        end
+
+        def run
+          return if @project_ids.nil? || @project_ids.empty?
+
+          execute(QUERY % [@project_ids.join(",")]) # rubocop:disable Style/FormatString
+        end
+
+        private
+
+        def execute(query)
+          with_connection_pool do |conn|
+            conn.exec(query)
+          end
+        rescue PG::UndefinedTable, PG::UndefinedColumn
+          nil
+        end
+      end
+
+      # The prober which is called when gathering metrics
+      class RemoteMirrorsProber
+        def initialize(opts, metrics: PrometheusMetrics.new)
+          @metrics = metrics
+          @collector = RemoteMirrorsCollector.new(
+            connection_string: opts[:connection_string],
+            project_ids: opts[:project_ids]
+          )
+        end
+
+        def probe_db
+          results = @collector.run
+          results.to_a.each do |row|
+            last_successful_update_at = row.delete("last_successful_update_at").to_i
+
+            @metrics.add(
+              "project_remote_mirror_last_successful_update_time_seconds",
+              last_successful_update_at,
+              project_id: row["project_id"],
+              url: row["url"]
+            )
+          end
+
+          self
+        rescue PG::ConnectionBad
+          self
+        end
+
+        def write_to(target)
+          target.write(@metrics.to_s)
+        end
+      end
+    end
+  end
+end

lib/gitlab_monitor/version.rb

 module GitLab
   module Monitor
-    VERSION = "3.5.0".freeze
+    VERSION = "3.6.0".freeze
   end
 end