if those servers are started from the very beginning, you can specify the server list in the following format:
The servers are simply separated by semicolon.
However, this is not necessary. The Hot Rod client will be aware of all server forming the cluster. All you need to do is to use "distribution" mode with numOwners=2. Then both of your servers will hold a copy of the data and when one of them crashes, the other one will be the backup.
Example configuration can be found at https://github.com/infinispan/infinispan/blob/master/core/src/main/resources/config-samples/sample.xml#L513