What are two reasons that would require an administrator to install the Events Service cluster...

According to the Cisco AppDynamics Professional Implementer (CAPI) documents, the two reasons that would require an administrator to install the Events Service cluster manually are:

Security concerns with passwordless SSH (B): This is a valid reason because the automated installation of the Events Service cluster requires passwordless SSH access to the target hosts. Passwordless SSH allows the Enterprise Console to execute commands on the remote hosts without prompting for a password. However, some organizations may have security policies that prohibit passwordless SSH access, as it may pose a risk of unauthorized access or malicious attacks. In such cases, the administrator can install the Events Service cluster manually, by following the steps described in the Manual Installation of the Events Service Cluster document1.

Security requirements to install using a non-root user account ©: This is a valid reason because the automated installation of the Events Service cluster requires root privileges on the target hosts. Root privileges allow the Enterprise Console to create directories, change permissions, and install packages on the remote hosts. However, some organizations may have security policies that restrict root access, as it may pose a risk of accidental or intentional damage to the system. In such cases, the administrator can install the Events Service cluster manually, by following the steps described in the Manual Installation of the Events Service Cluster document1. The administrator can use a non-root user account that has sudo privileges to perform the manual installation.

The incorrect options are:

Installation on SUSE Linux (A): This is not a valid reason for manual installation, because the automated installation of the Events Service cluster supports SUSE Linux as one of the compatible operating systems. The Enterprise Console can install the Events Service cluster on SUSE Linux hosts using the automated installation process, as long as the hosts meet the prerequisites described in the Events Service Requirements document2.

Installation on Windows (D): This is not a valid reason for manual installation, because the Events Service cluster does not support Windows as an operating system. The Events Service cluster can only run on Linux hosts, as it is based on Apache Cassandra, which is a Linux-based distributed database. The Events Service cluster cannot be installed on Windows hosts, either manually or automatically2.

References:

1: Manual Installation of the Events Service Cluster - AppDynamics

2: Events Service Requirements - AppDynamics