Merge pull request #180 from alphagov/metrics

Add initial metrics support

app/services/discovery_engine/query/search.rb

@@ -29,7 +29,10 @@ def result_set
     attr_reader :query_params, :client
 
     def response
-      @response ||= client.search(discovery_engine_params).response
+      @response ||= begin
+        Metrics.increment_counter(:search_requests)
+        client.search(discovery_engine_params).response
+      end
     end
 
     def discovery_engine_params

app/services/discovery_engine/sync/delete.rb

@@ -11,6 +11,7 @@ def call(content_id, payload_version: nil)
       client.delete_document(name: document_name(content_id))
 
       log(Logger::Severity::INFO, "Successfully deleted", content_id:, payload_version:)
+      Metrics.increment_counter(:delete_requests)
     rescue Google::Cloud::NotFoundError => e
       log(
         Logger::Severity::INFO,
@@ -24,6 +25,7 @@ def call(content_id, payload_version: nil)
         content_id:, payload_version:,
       )
       GovukError.notify(e)
+      Metrics.increment_counter(:failed_delete_requests)
     end
 
   private

app/services/discovery_engine/sync/put.rb

@@ -25,13 +25,15 @@ def call(content_id, metadata, content: "", payload_version: nil)
       )
 
       log(Logger::Severity::INFO, "Successfully added/updated", content_id:, payload_version:)
+      Metrics.increment_counter(:put_requests)
     rescue Google::Cloud::Error => e
       log(
         Logger::Severity::ERROR,
         "Failed to add/update document due to an error (#{e.message})",
         content_id:, payload_version:,
       )
       GovukError.notify(e)
+      Metrics.increment_counter(:failed_put_requests)
     end
 
   private

app/services/metrics.rb

@@ -0,0 +1,28 @@
+module Metrics
+  CLIENT = PrometheusExporter::Client.default
+  COUNTERS = {
+    search_requests: CLIENT.register(
+      :counter, "search_api_v2_search_requests", "number of incoming search requests"
+    ),
+    put_requests: CLIENT.register(
+      :counter, "search_api_v2_put_requests", "number of put requests to Discovery Engine"
+    ),
+    delete_requests: CLIENT.register(
+      :counter, "search_api_v2_put_requests", "number of delete requests to Discovery Engine"
+    ),
+    failed_put_requests: CLIENT.register(
+      :counter, "search_api_v2_failed_put_requests", "number of failed put requests to Discovery Engine"
+    ),
+    failed_delete_requests: CLIENT.register(
+      :counter, "search_api_v2_failed_delete_requests", "number of failed delete requests to Discovery Engine"
+    ),
+  }.freeze
+
+  def self.increment_counter(counter)
+    Rails.logger.warn("Unknown counter: #{counter}") and return unless COUNTERS.key?(counter)
+
+    COUNTERS[counter].observe(1)
+  rescue StandardError
+    # Metrics are best effort only, don't raise if they fail
+  end
+end