Late-bind DNS resolutions

[kevinballard]

Change the internal host information from SocketAddress to an internal
HostPort class. Only resolve the HostPort into an InetSocketAddress right
before a connection (or reconnection) is made. This allows changes in DNS
mappings to be detected (e.g. when using AWS Elastic IPs).

[kevinballard]

This addresses Issue 245.

[daschl]

Hi @kevinballard oh wow that is a large fix. Do you know if this late binding has performance impact?

[kevinballard]

It looks like a large change, but the majority of it is just swapping one type for another.

The late binding does have a slight performance impact, but no more than it should for the desired behavior. The initial connection setup and any reconnections can cause a DNS lookup, if the JVM or the OS don't have it cached. With default configurations the JVM will cache DNS lookups for 30 seconds, and I believe that most OS'es will respect the TTLs on the DNS records themselves.