Stripe: do not include path ids in metric names

lib/new_relic/agent/instrumentation/stripe_subscriber.rb

@@ -10,6 +10,7 @@ class StripeSubscriber
         EVENT_ATTRIBUTES = %i[http_status method num_retries path request_id].freeze
         ATTRIBUTE_NAMESPACE = 'stripe.user_data'
         ATTRIBUTE_FILTER_TYPES = %i[include exclude].freeze
+        PATH_PORTION_PATTERN = %r{^/([^/]+/[^/]+)(?:/|\z)}.freeze
 
         def start_segment(event)
           return unless is_execution_traced?
@@ -39,7 +40,27 @@ def is_execution_traced?
         end
 
         def metric_name(event)
-          "Stripe#{event.path}/#{event.method}"
+          # Grab only the first 2 items from the slash (/) delimited event path.
+          # These items are the API version string and the category. Grabbing
+          # any more of the path will result in unique method names that will
+          # easily grow to be too numerous to sort through in the UI and
+          # possibly even violate default New Relic metric count thresholds.
+          # See newrelic/newrelic-ruby-agent#2654 and
+          # newrelic/newrelic-ruby-agent#2709 for more details.
+          #
+          # In Ruby v3.4 benchmarks, using regex to get at the first two path
+          # elements was seen as more performant than using String#split.
+          #
+          # Regex legend:
+          #
+          # ^ = starts with
+          # / = a literal '/'
+          # () = capture
+          # (?:) = don't capture
+          # [^/]+ = 1 or more characters that are not '/'
+          # /|\z = a literal '/' OR the end of the string
+          path_portion = event.path =~ PATH_PORTION_PATTERN ? Regexp.last_match(1) : NewRelic::UNKNOWN
+          "Stripe/#{path_portion}/#{event.method}"
         end
 
         def add_stripe_attributes(segment, event)

test/multiverse/suites/stripe/stripe_instrumentation_test.rb

@@ -10,6 +10,7 @@
 class StripeInstrumentation < Minitest::Test
   API_KEY = '123456789'
   STRIPE_URL = 'Stripe/v1/customers/get'
+  DummyEvent = Struct.new(:path, :method)
 
   def setup
     Stripe.api_key = API_KEY
@@ -168,6 +169,27 @@ def test_start_segment_records_error
     end
   end
 
+  def test_metric_names_are_not_specific_enough_to_cause_a_cardinality_explosion
+    categories = %w[Trzy_kolory The_Apu_Trilogy The_Lord_of_the_Rings]
+    paths = ["/v1/#{categories[0]}/Niebieski",
+      "/v1/#{categories[0]}/Biały",
+      "/v1/#{categories[0]}/Czerwony",
+      "/v1/#{categories[1]}/Pather_Panchali",
+      "/v1/#{categories[1]}/Aparajito",
+      "/v1/#{categories[1]}/The_World_of_Apu",
+      "/v1/#{categories[2]}/The_Fellowship_of_the_Ring",
+      "/v1/#{categories[2]}/The_Two_Towers",
+      "/v1/#{categories[2]}/The_Return_of_the_King"]
+    method = 'get'
+
+    subscriber = NewRelic::Agent::Instrumentation::StripeSubscriber.new
+    expected = categories.map { |c| Array.new(3) { "Stripe/v1/#{c}/#{method}" } }.flatten
+    actual = paths.map { |p| subscriber.send(:metric_name, DummyEvent.new(p, method)) }
+
+    assert_equal expected, actual,
+      "Expected everything after the category in each path to be stripped away. Expected: #{expected} Actual: #{actual}"
+  end
+
   def start_stripe_event
     Stripe::Customer.list({limit: 3})
   end