Support IP changes of statsd hostname

lib/datadog/statsd/udp_connection.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative 'connection'
+require "resolv"
 
 module Datadog
   class Statsd
@@ -35,12 +36,30 @@ def connect
         @socket.connect(host, port)
       end
 
+      def check_dns_resolution
+        unless @current_host_ip && @last_dns_check
+          @current_host_ip = Resolv.getaddress(@host)
+          @last_dns_check = Time.now
+        end
+
+        return if Time.now - @last_dns_check < 60
+
+        @last_dns_check = Time.now
+        fresh_resolved_ip = Resolv.getaddress(@host)
+        return if @current_host_ip == fresh_resolved_ip
+
+        @current_host_ip = fresh_resolved_ip
+        close
+        connect
+      end
+
       # send_message is writing the message in the socket, it may create the socket if nil
       # It is not thread-safe but since it is called by either the Sender bg thread or the
       # SingleThreadSender (which is using a mutex while Flushing), only one thread must call
       # it at a time.
       def send_message(message)
         connect unless @socket
+        check_dns_resolution
         @socket.send(message, 0)
       end
     end

spec/integrations/connection_edge_case_spec.rb

@@ -21,6 +21,7 @@
 
     let(:fake_socket) do
       instance_double(UDPSocket,
+        close: true,
         connect: true,
         send: true)
     end
@@ -31,6 +32,63 @@
         send: true)
     end
 
+    context 'when hostname resolves to a different ip address after connecting' do
+      it 'reconnects socket after 60 seconds if the ip changes' do
+        allow(Resolv).to receive(:getaddress)
+          .and_return("192.168.0.1", "192.168.0.2")
+
+        subject.write('foobar')
+        expect(fake_socket)
+          .to have_received(:send)
+          .with('foobar', anything)
+
+        subject.write('foobar')
+        expect(fake_socket)
+          .to have_received(:send)
+          .with('foobar', anything)
+          .twice
+
+        Timecop.travel(Time.now + 61) do
+          subject.write('foobar')
+          expect(fake_socket_retry)
+            .to have_received(:send)
+            .with('foobar', anything)
+        end
+
+        Timecop.travel(Time.now + 360) do
+          subject.write('foobar')
+          expect(fake_socket_retry)
+            .to have_received(:send)
+            .with('foobar', anything)
+            .twice
+        end
+      end
+
+      it 'does not reconnect socket after 60 seconds if the ip does not change' do
+        allow(Resolv).to receive(:getaddress)
+          .and_return("192.168.0.1")
+
+        subject.write('foobar')
+        expect(fake_socket)
+          .to have_received(:send)
+          .with('foobar', anything)
+
+        subject.write('foobar')
+        expect(fake_socket)
+          .to have_received(:send)
+          .with('foobar', anything)
+          .twice
+
+        Timecop.travel(Time.now + 61) do
+          subject.write('foobar')
+          expect(fake_socket)
+            .to have_received(:send)
+            .with('foobar', anything)
+            .exactly(3).times
+        end
+      end
+    end
+
     context 'when having unknown SocketError (drop strategy)'do
       before do
         allow(fake_socket)