fix: Improve remote evaluation fetch retry logic

lib/amplitude-experiment.rb

@@ -15,6 +15,7 @@
 require 'experiment/local/assignment/assignment_config'
 require 'experiment/util/lru_cache'
 require 'experiment/util/hash'
+require 'experiment/error'
 
 # Amplitude Experiment Module
 module AmplitudeExperiment

lib/experiment/error.rb

@@ -0,0 +1,11 @@
+module AmplitudeExperiment
+  # FetchError
+  class FetchError < StandardError
+    attr_reader :status_code
+
+    def initialize(status_code, message)
+      super(message)
+      @status_code = status_code
+    end
+  end
+end

lib/experiment/remote/client.rb

@@ -61,12 +61,14 @@ def fetch_internal(user)
       do_fetch(user, @config.fetch_timeout_millis)
     rescue StandardError => e
       @logger.error("[Experiment] Fetch failed: #{e.message}")
-      begin
-        return retry_fetch(user)
-      rescue StandardError => err
-        @logger.error("[Experiment] Retry Fetch failed: #{err.message}")
+      if should_retry_fetch?(e)
+        begin
+          retry_fetch(user)
+        rescue StandardError => err
+          @logger.error("[Experiment] Retry Fetch failed: #{err.message}")
+        end
       end
-      throw e
+      raise e
     end
 
     # @param [User] user
@@ -108,6 +110,8 @@ def do_fetch(user, timeout_millis)
       end_time = Time.now
       elapsed = (end_time - start_time) * 1000.0
       @logger.debug("[Experiment] Fetch complete in #{elapsed.round(3)} ms")
+      raise FetchError.new(response.code.to_i, "Fetch error response: status=#{response.code} #{response.message}") if response.code != '200'
+
       json = JSON.parse(response.body)
       variants = parse_json_variants(json)
       @logger.debug("[Experiment] Fetched variants: #{variants}")
@@ -140,5 +144,11 @@ def add_context(user)
       user.library = "experiment-ruby-server/#{VERSION}"
       user
     end
+
+    def should_retry_fetch?(err)
+      return err.status_code < 400 || err.status_code >= 500 || err.status_code == 429 if err.is_a?(FetchError)
+
+      true
+    end
   end
 end