When you use the Elastic template found here to Azure, does it use the Azure Discovery Plugin or is it using unicast ? If using unicast, how do you handle when a machine dies and a new one is brought up with a new IP ?
The ARM template does not use the Azure Discovery plugin at this current time. It uses a list of unicast hosts where the hostnames of the machines are used. For example, if using dedicated master nodes it will use the following in configuration
discovery.zen.ping.unicast.hosts: [${PREFIX}master-0:9300",${PREFIX}master-1:9300",${PREFIX}master-2:9300"]
where ${PREFIX} is the value for vmHostNamePrefix specified in the template (labelled as "Hostname prefix" in the portal). The default prefix is empty, but must be used if deploying more than one cluster to the same VNet.
In using hostnames, it doesn't matter what IP addresses are assigned to VMs in the cluster; if a VM goes down, a new one will come up with the same hostname.