What is the minimum recommended number of controllers for a Cisco APIC cluster?

The recommended minimum number of controllers for a Cisco Application Policy Infrastructure Controller (APIC) cluster is three. This configuration is essential for ensuring high availability and fault tolerance within the cluster.

Having three controllers allows the cluster to maintain a quorum, which is crucial for making decisions and continuing operations even if one controller fails. In a distributed system, a quorum is the minimum number of members required to be operational and agree on decisions, effectively ensuring that the cluster remains functional and consistent.

By utilizing three controllers, the cluster can withstand the loss of one controller without disrupting service or compromising the integrity of the management system. This setup supports increased reliability and resilience, which are critical for maintaining an efficient and stable data center environment. While having two controllers might seem sufficient for redundancy, it does not provide the necessary quorum needed in the event of a failure, making three the ideal number for optimal performance and availability.