Run at least 2 instances of each role within a cloud service. When we have 2 or more instances running for a role in cloud service then automatically the deployment gets distributed across different fault and upgrade domains and achieves almost or near to zero downtime.
Deep Dive:
Fault domain is a physical unit of failure. In simple form when your computer is connected to power supply and if power supply is down then your computer can not be operational. So computer itself connected to power supply is a Fault domain.
Definition - So a fault domain is set of hardware components like computers, switches that share single point of failure.
