out_http: Add option to reuse connections

lib/fluent/plugin/out_http.rb

@@ -37,6 +37,8 @@ class HTTPOutput < Output
 
     class RetryableResponse < StandardError; end
 
+    ConnectionCache = Struct.new(:uri, :conn)
+
     helpers :formatter
 
     desc 'The endpoint for HTTP request, e.g. http://example.com/api'
@@ -60,6 +62,8 @@ class RetryableResponse < StandardError; end
     config_param :read_timeout, :integer, default: nil
     desc 'The TLS timeout in seconds'
     config_param :ssl_timeout, :integer, default: nil
+    desc 'Try to reuse connections'
+    config_param :reuse_connections, :bool, default: false
 
     desc 'The CA certificate path for TLS'
     config_param :tls_ca_cert_path, :string, default: nil
@@ -100,17 +104,41 @@ class RetryableResponse < StandardError; end
       config_param :aws_role_arn, :string, default: nil
     end
 
+    def connection_cache_id_thread_key
+      "#{plugin_id}_connection_cache_id"
+    end
+
+    def connection_cache_id_for_thread
+      Thread.current[connection_cache_id_thread_key]
+    end
+
+    def connection_cache_id_for_thread=(id)
+      Thread.current[connection_cache_id_thread_key] = id
+    end
+
     def initialize
       super
 
       @uri = nil
       @proxy_uri = nil
       @formatter = nil
+
+      @connection_cache = []
+      @connection_cache_id_mutex = Mutex.new
+      @connection_cache_next_id = 0
+    end
+
+    def close
+      super
+
+      @connection_cache.each {|entry| entry.conn.finish if entry.conn&.started? }
     end
 
     def configure(conf)
       super
 
+      @connection_cache = Array.new(actual_flush_thread_count, ConnectionCache.new("", nil)) if @reuse_connections
+
       if @retryable_response_codes.nil?
         log.warn('Status code 503 is going to be removed from default `retryable_response_codes` from fluentd v2. Please add it by yourself if you wish')
         @retryable_response_codes = [503]
@@ -302,16 +330,41 @@ def create_request(chunk, uri)
       req
     end
 
+    def make_request_cached(uri, req)
+      id = self.connection_cache_id_for_thread
+      if id.nil?
+        @connection_cache_id_mutex.synchronize {
+          id = @connection_cache_next_id
+          @connection_cache_next_id += 1
+        }
+        self.connection_cache_id_for_thread = id
+      end
+      uri_str = uri.to_s
+      if @connection_cache[id].uri != uri_str
+        @connection_cache[id].conn.finish if @connection_cache[id].conn&.started?
+        http =  if @proxy_uri
+                  Net::HTTP.start(uri.host, uri.port, @proxy_uri.host, @proxy_uri.port, @proxy_uri.user, @proxy_uri.password, @http_opt)
+                else
+                  Net::HTTP.start(uri.host, uri.port, @http_opt)
+                end
+        @connection_cache[id] = ConnectionCache.new(uri_str, http)
+      end
+      @connection_cache[id].conn.request(req)
+    end
+
+    def make_request(uri, req, &block)
+      if @proxy_uri
+        Net::HTTP.start(uri.host, uri.port, @proxy_uri.host, @proxy_uri.port, @proxy_uri.user, @proxy_uri.password, @http_opt, &block)
+      else
+        Net::HTTP.start(uri.host, uri.port, @http_opt, &block)
+      end
+    end
 
     def send_request(uri, req)
-      res = if @proxy_uri
-              Net::HTTP.start(uri.host, uri.port, @proxy_uri.host, @proxy_uri.port, @proxy_uri.user, @proxy_uri.password, @http_opt) { |http|
-                http.request(req)
-              }
+      res = if @reuse_connections
+              make_request_cached(uri, req)
             else
-              Net::HTTP.start(uri.host, uri.port, @http_opt) { |http|
-                http.request(req)
-              }
+              make_request(uri, req) { |http| http.request(req) }
             end
 
       if res.is_a?(Net::HTTPSuccess)

test/plugin/test_out_http.rb

@@ -518,4 +518,40 @@ def test_write_with_https
       assert_not_empty result.headers
     end
   end
+
+  sub_test_case 'connection_reuse' do
+    def server_port
+      19883
+    end
+
+    def test_connection_recreation
+      d = create_driver(%[
+        endpoint http://127.0.0.1:#{server_port}/test
+        reuse_connections true
+      ])
+
+      d.run(default_tag: 'test.http', shutdown: false) do
+        d.feed(test_events[0])
+      end
+
+      data = @@result.data
+
+      # Restart server to simulate connection loss
+      @@http_server_thread.kill
+      @@http_server_thread.join
+      @@http_server_thread = Thread.new do
+        run_http_server
+      end
+
+      d.run(default_tag: 'test.http') do
+        d.feed(test_events[1])
+      end
+
+      result = @@result
+      assert_equal 'POST', result.method
+      assert_equal 'application/x-ndjson', result.content_type
+      assert_equal test_events, data.concat(result.data)
+      assert_not_empty result.headers
+    end
+  end
 end