I have custom co-processors that I need to make available to HBase. Do I copy my jar files into a lib directory somewhere? Use Ambari to append to a RegionServer classpath environment variable?
The book will cover what properties to set in hbase-site.xml which you can do via Ambari. However, it will depend on you copying out the necessary jar(s) to your cluster as well (/usr/hdp/current/hbase-client/lib should do the trick).
Loading jars out of HDFS, as enabled by HBASE-1936, would be an alternative to copying the jars to the local filesystem on each node running HBase.