Expire channel when its remote address not valid after remote DNS update

[russellyou]

At the moment a channel will expire when either

1 idleTimeoutExpired
2 channel closed by remote end
3 channel TTL expired

But there is one special case making channel not usable. We use AHC to connect to a service behind AWS ALB. When a new deployment happens, the DNS of service will be changed targeting new deployed vesion . But for a period of time(say 1 hour), old version and new version services co-exist. During the hour, the channel of old version service can still be used . But that's not as expected.

Could we update the DefaultChannelPool.IdleChannelDetector to add check
if channel's remoteAddess is not in list of DNS resolve result , we will mark this channel as expired.

Happy to raise a PR for this.

code in DefaultChannelPool.IdleChannelDetector

    private List<IdleChannel> expiredChannels(ConcurrentLinkedDeque<IdleChannel> partition, long now) {
      // lazy create
      List<IdleChannel> idleTimeoutChannels = null;
      for (IdleChannel idleChannel : partition) {
        boolean isIdleTimeoutExpired = isIdleTimeoutExpired(idleChannel, now);
        boolean isRemotelyClosed = !Channels.isChannelActive(idleChannel.channel);
        boolean isTtlExpired = isTtlExpired(idleChannel.channel, now);
        if (isIdleTimeoutExpired || isRemotelyClosed || isTtlExpired) {
          LOGGER.debug("Adding Candidate expired Channel {} isIdleTimeoutExpired={} isRemotelyClosed={} isTtlExpired={}", idleChannel.channel, isIdleTimeoutExpired, isRemotelyClosed, isTtlExpired);
          if (idleTimeoutChannels == null)
            idleTimeoutChannels = new ArrayList<>(1);
          idleTimeoutChannels.add(idleChannel);
        }
      }

      return idleTimeoutChannels != null ? idleTimeoutChannels : Collections.emptyList();
    }