0001-Don-t-send-AAAA-DNS-request-when-domain-resolved-to-.patch

From e11c45a6386cd9eba16be5b56298b2cbba0db167 Mon Sep 17 00:00:00 2001
From: Ihar Hrachyshka <ihrachys@redhat.com>
Date: Sat, 10 Jun 2017 13:07:17 -0700
Subject: [PATCH] Don't send AAAA DNS request when domain resolved to IPv4
 address

There is no need to send both A and AAAA requests when connecting to a
host since we are interested in a single address only. So if the host
resolves into IPv4 address, we can skip request for AAAA since it will
not be used anyway.

This sounds like a minor optimization, but it comes as a huge win in
case where DNS resolver is not configured for the requested host name,
but the name is listed in /etc/hosts with a IPv4 address. In this case,
resolution is very quick (the file is local, so no DNS request is sent),
except for the fact that we still ask for AAAA record for the host name.
A misconfigured DNS resolver can take time until it will time out the
request (30 seconds is a common length for Linux), which is an
unnecessary delay.

This exact situation hit OpenStack TripleO CI where DNS was not
configured, but resolution is implemented via /etc/hosts file which did
not include IPv6 entries.

OpenStack bug: https://bugs.launchpad.net/neutron/+bug/1696094
---
 amqp/transport.py | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/amqp/transport.py b/amqp/transport.py
index 981c8b6..771e00e 100644
--- a/amqp/transport.py
+++ b/amqp/transport.py
@@ -149,26 +149,28 @@ class _AbstractTransport(object):
                     sock.settimeout(prev)
 
     def _connect(self, host, port, timeout):
-        entries = socket.getaddrinfo(
-            host, port, 0, socket.SOCK_STREAM, SOL_TCP,
-        )
-        for i, res in enumerate(entries):
-            af, socktype, proto, canonname, sa = res
-            try:
-                self.sock = socket.socket(af, socktype, proto)
+        # avoid additional DNS requests for AAAA if A succeeds
+        for family in (socket.AF_INET, socket.AF_INET6):
+            entries = socket.getaddrinfo(
+                host, port, family, socket.SOCK_STREAM, SOL_TCP,
+            )
+            for i, res in enumerate(entries):
+                af, socktype, proto, canonname, sa = res
                 try:
-                    set_cloexec(self.sock, True)
-                except NotImplementedError:
-                    pass
-                self.sock.settimeout(timeout)
-                self.sock.connect(sa)
-            except socket.error:
-                self.sock.close()
-                self.sock = None
-                if i + 1 >= len(entries):
-                    raise
-            else:
-                break
+                    self.sock = socket.socket(af, socktype, proto)
+                    try:
+                        set_cloexec(self.sock, True)
+                    except NotImplementedError:
+                        pass
+                    self.sock.settimeout(timeout)
+                    self.sock.connect(sa)
+                except socket.error:
+                    self.sock.close()
+                    self.sock = None
+                    if i + 1 >= len(entries):
+                        raise
+                else:
+                    return
 
     def _init_socket(self, socket_settings, read_timeout, write_timeout):
         try:
-- 
2.9.4