Support for High Availability on VM-Series on Azure
Traditional HA configuration is not relevant in Azure.
For HA, use cloud-native load balancers such as the Azure Application
VM-Series on Azure does not support the traditional
active/passive high availability with session synchronization, as
it is not a good fit for the public cloud architecture where you
don’t need to protect against hardware failures (CPU, memory, NIC,
HDD) like you would in a private cloud deployment. Instead, for both
small and large deployments, use a scale out architecture using
cloud-native load balancers such as the Azure Application Gateway
or Azure Load Balancer to distribute traffic across a set of healthy
instances of the firewall. For details, For details, see Deploy
the VM-Series and Azure Application Gateway Template.