fix(irc-puppet): pick a random IPv6 address to connect to IRC hosts

dibridge/irc_puppet.py

@@ -1,6 +1,7 @@
 import asyncio
 import irc.client_aio
 import logging
+import random
 import socket
 
 
@@ -135,14 +136,28 @@ async def reclaim_nick(self):
         self._client.nick(self._nickname)
 
     async def connect(self):
-        self._log.info("Connecting to IRC from %s ...", self._ipv6_address)
-
         local_addr = (str(self._ipv6_address), 0)
 
         while self._reconnect:
+            # As per RFC, libc sorts IPv6 results in some complicated way. In result,
+            # even if the IRC host has multiple IPv6 addresses listed, we will pick
+            # almost always the same one. This gives unneeded pressure on a single
+            # host, instead of distributing the load. So instead, we do the lookup
+            # ourselves, and pick a random one.
+            ipv6s = await self.loop.getaddrinfo(self._irc_host, None, socket.AF_INET6, socket.SOCK_STREAM, socket.IPPROTO_TCP)
+            if not ipv6s:
+                self._log.warning("Failed DNS lookup, retrying in 5 seconds")
+                # When we can't connect, try again in 5 seconds.
+                await asyncio.sleep(5)
+                continue
+
+            irc_host_ipv6 = random.choice(ipv6s)[4][0]
+
+            self._log.info("Connecting to IRC from %s to %s (%s) ...", self._ipv6_address, self._irc_host, irc_host_ipv6)
+
             try:
                 await self.connection.connect(
-                    self._irc_host,
+                    irc_host_ipv6,
                     self._irc_port,
                     self._nickname,
                     username=self._username,