diff --git a/lib/fluent/plugin/in_prometheus.rb b/lib/fluent/plugin/in_prometheus.rb
index f2d64c4..806c3a9 100644
--- a/lib/fluent/plugin/in_prometheus.rb
+++ b/lib/fluent/plugin/in_prometheus.rb
@@ -32,12 +32,6 @@ class PrometheusInput < Fluent::Plugin::Input
       config_param :extra_conf, :hash, default: {:SSLCertName => [['CN','nobody'],['DC','example']]}, symbolize_keys: true
     end
 
-    attr_reader :registry
-
-    attr_reader :num_workers
-    attr_reader :base_port
-    attr_reader :metrics_path
-
     def initialize
       super
       @registry = ::Prometheus::Client.registry
@@ -100,8 +94,22 @@ def start
       end
 
       @server = WEBrick::HTTPServer.new(config)
-      @server.mount(@metrics_path, MonitorServlet, self)
-      @server.mount(@aggregated_metrics_path, MonitorServletAll, self)
+      @server.mount_proc(@metrics_path) do |_req, res|
+        status, header, body = all_metrics
+        res.status = status
+        res['Content-Type'] = header['Content-Type']
+        res.body = body
+        res
+      end
+
+      @server.mount_proc(@aggregated_metrics_path) do |_req, res|
+        status, header, body = all_workers_metrics
+        res.status = status
+        res['Content-Type'] = header['Content-Type']
+        res.body = body
+        res
+      end
+
       thread_create(:in_prometheus) do
         @server.start
       end
@@ -115,49 +123,40 @@ def shutdown
       super
     end
 
-    class MonitorServlet < WEBrick::HTTPServlet::AbstractServlet
-      def initialize(server, prometheus)
-        @prometheus = prometheus
-      end
+    def all_metrics
+      [200, { 'Content-Type' => ::Prometheus::Client::Formats::Text::CONTENT_TYPE }, ::Prometheus::Client::Formats::Text.marshal(@registry)]
+    rescue => e
+      [500, { 'Content-Type' => 'text/plain' }, e.to_s]
+    end
+
+    def all_workers_metrics
+      full_result = PromMetricsAggregator.new
 
-      def do_GET(req, res)
-        res.status = 200
-        res['Content-Type'] = ::Prometheus::Client::Formats::Text::CONTENT_TYPE
-        res.body = ::Prometheus::Client::Formats::Text.marshal(@prometheus.registry)
-      rescue
-        res.status = 500
-        res['Content-Type'] = 'text/plain'
-        res.body = $!.to_s
+      send_request_to_each_worker do |resp|
+        if resp.is_a?(Net::HTTPSuccess)
+          full_result.add_metrics(resp.body)
+        end
       end
+
+      [200, { 'Content-Type' => ::Prometheus::Client::Formats::Text::CONTENT_TYPE }, full_result.get_metrics]
+    rescue => e
+      [500, { 'Content-Type' => 'text/plain' }, e.to_s]
     end
 
-    class MonitorServletAll < WEBrick::HTTPServlet::AbstractServlet
-      def initialize(server, prometheus)
-        @prometheus = prometheus
+    def send_request_to_each_worker
+      bind = (@bind == '0.0.0.0') ? '127.0.0.1' : @bind
+      req = Net::HTTP::Get.new(@metrics_path)
+      [*(@base_port...(@base_port + @num_workers))].each do |worker_port|
+        do_request(host: bind, port: worker_port) do |http|
+          yield(http.request(req))
+        end
       end
+    end
 
-      def do_GET(req, res)
-        res.status = 200
-        res['Content-Type'] = ::Prometheus::Client::Formats::Text::CONTENT_TYPE
-
-        full_result = PromMetricsAggregator.new
-        fluent_server_ip = @prometheus.bind == '0.0.0.0' ? '127.0.0.1' : @prometheus.bind
-        current_worker = 0
-        while current_worker < @prometheus.num_workers
-          Net::HTTP.start(fluent_server_ip, @prometheus.base_port + current_worker) do |http|
-            req = Net::HTTP::Get.new(@prometheus.metrics_path)
-            result = http.request(req)
-            if result.is_a?(Net::HTTPSuccess)
-              full_result.add_metrics(result.body)
-            end
-          end
-          current_worker += 1
-        end
-        res.body = full_result.get_metrics
-      rescue
-        res.status = 500
-        res['Content-Type'] = 'text/plain'
-        res.body = $!.to_s
+    def do_request(host:, port:)
+      http = Net::HTTP.new(host, port)
+      http.start do
+        yield(http)
       end
     end
   end