DnsServerList.java

import com.netflix.loadbalancer.Server;
import com.netflix.loadbalancer.ServerList;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.Security;
import java.util.ArrayList;
import java.util.List;

/**
 * Creates a list of servers based on resolving the IP addresses of a hostname through DNS.
 * Useful when the DNS A-record holds multiple IP addresses that you want to load-balance over.
 */
public class DnsServerList implements ServerList<Server> {

    private Logger logger = LoggerFactory.getLogger(getClass());
    private String hostname;

    public DnsServerList(String hostname) {
        this.hostname = hostname;
        try {
            Security.setProperty("networkaddress.cache.ttl", "0");
        } catch (SecurityException e) {
            logger.warn("Can't disable DNS cache", e);
        }
    }

    @Override
    public List<Server> getInitialListOfServers() {
        return getUpdatedListOfServers();
    }

    @Override
    public List<Server> getUpdatedListOfServers() {
        List<Server> servers = new ArrayList<>();
        try {
            for (InetAddress address : InetAddress.getAllByName(hostname)) {
                servers.add(new Server(address.getHostAddress()));
            }
        } catch (UnknownHostException e) {
            logger.error("Can't resolve {}: {}", hostname, e.getMessage());
        }
        logger.debug("Resolved {} to {} Servers", hostname, servers.size());
        return servers;
    }
}