If your services (eg: HDFS, HBase) are marked as dependent on that
ZooKeeper service, then the ensemble will a part of their config
(hdfs-site.xml, hbase-site.xml). If your application uses HBase for
example, then mark the node as a gateway which will deploy the config in
/etc/hbase, then let your app use those.
If you're running a custom app that has its own set of config files, then
you should provide all ZooKeeper servers. Pointing to only one would mean
you might face an outage if it is down. The ZooKeeper client libraries know
how to deal with multiple servers and switch connections if one goes down.
Regards,
Gautam Gopalakrishnan