High availability increases resiliency to failure by creating two project instances that run simultaneously.
When a project is deployed in HA (active-active) mode, two instances are created: primary and secondary. Whether the project is in HA mode or not, you can set affinity and cold failover options for each instance, including failover intervals and failure per interval options. Non-HA projects have one instance, numbered 0 (zero). HA project instances are numbered 0 and 1. Some commands require instance numbers to identify instances of a project.