Explanation
According to the Cisco AppDynamics Professional Implementer (CAPI) documents, the minimum recommended number of nodes for a redundant Events Service is three ©. The Events Service is a distributed database that stores and processes the analytics data collected by the AppDynamics platform. The Events Service cluster consists of multiple nodes that share the data load and provide fault tolerance and high availability. The minimum number of nodes for a functional Events Service cluster is one, but this is not recommended for production environments, as it does not provide any redundancy or resilience. The minimum number of nodes for a redundant Events Service cluster is three, as this allows the cluster to tolerate the failure of one node without losing any data or availability. The recommended number of nodes for a redundant Events Service cluster is five or more, as this provides better performance and scalability12.
The incorrect options are:
1 (A): This is not a valid option because a single-node Events Service cluster does not provide any redundancy or resilience. If the node fails, the cluster becomes unavailable and the data is lost. A single-node Events Service cluster is only suitable for testing or development purposes, not for production environments12.
2 (B): This is not a valid option because a two-node Events Service cluster does not provide sufficient redundancy or resilience. If one node fails, the cluster becomes unstable and may lose data or availability. A two-node Events Service cluster is not recommended for production environments12.
4 (D): This is not a valid option because a four-node Events Service cluster is not optimal for redundancy or resilience. A four-node Events Service cluster has an even number of nodes, which may cause a split-brain scenario, where the cluster is divided into two equal partitions that cannot communicate with each other. This may result in data inconsistency or unavailability. A four-node Events Service cluster can be improved by adding a fifth node to avoid the split-brain scenario12.
References:
1: Events Service Deployment - AppDynamics
2: Events Service Requirements - AppDynamics