Defining a DataSource in TomEE is quite easy, the most common way to do so is to define a Resource block in tomee.xml:
<Resource id="jdbc/ds" type="DataSource"> JdbcUrl = jdbc:mysql://datasourcehost:3306/tomee ... </Resource>
When you have multiple hosts you often use datasourcehost (in the previous sample) as a service host (or IP) to delegate then to real hosts. But sometimes it is not possible or too complicated. For such needs TomEE now provides a basic failover feature.
The idea is to reuse dynamic datasource feature of tomee to handle it.