Java outgoing TCP connection failover based on multiple DNS results

Question

If I make a connection using new Socket("unit.domain.com", 100) and the unit.domain.com DNS record has multiple IP addresses in the A record.. In the event of a failed connection, Does Java automatically connect to one of the other addresses in the list like the browser does? or does that have to be implemented manually?

Answer 1

No! Creating a socket via new Socket(String, int) results in a resolving like that

addr = InetAddress.getByName(hostname);

which is a shortcut for

return InetAddress.getAllByName(host)[0];

The address resolution is performed in the Socket c-tor.

If you have to reconnect (failover) use the result returned by InetAddress.getAllByName(host), randomize (or use round-robin) and connect to the necessary addresses.

Edit: also if you are going to need to connect with some likely failure, you'd be better off using connect method of the Socket class with a timeout. Also make sure you close even failed sockets (and esp. channels) since they may leak a FD on *Nix.