According to the Cisco AppDynamics Professional Implementer (CAPI) documents, the correct method to perform a NET Agent upgrade is to perform the agent upgrade on the application server host by running the MSI Installer Package12. This method will install updated agent files and maintain legacy configurations. You do not need to uninstall the old agent first when you upgrade from the NET Agent >= 3.9, except for patch releases. You need to stop IIS, instrumented Windows services, and instrumented standalone applications before running the MSI Installer Package. You also need to launch an elevated command prompt with full administrator privileges and specify youraccount access key for single-tenant Controller accounts. After the installation, you need to restart Windows services and standalone applications.

The incorrect options are:

Perform the agent upgrade on a remote server host by using the AppDynamics Controller REST API. (B) This is not a valid method for upgrading the NET Agent, because the AppDynamics Controller REST API does not provide any endpoint for agent installation or upgrade. The REST API is mainly used for retrieving or updating configuration data, metrics, events, snapshots, and other information from the Controller3.

Perform the agent upgrade on the application server host by running the Agent Configuration Utility. © This is not a valid method for upgrading the NET Agent, because the Agent Configuration Utility is a tool for modifying the agent configuration after installation, not for installing or upgrading the agent. The Agent Configuration Utility allows you to change the Controller connection settings, the agent logging level, the proxy settings, and other advanced options4.

Perform the agent upgrade via the AppDynamics Controller UI. (D) This is not a valid method for upgrading the NET Agent, because the AppDynamics Controller UI does not provide any feature for agent installation or upgrade. The Controller UI is mainly used for monitoring, analyzing, and troubleshooting the performance of the applications, business transactions, tiers, nodes, and other entities that are instrumented by the agents5.

References:

1: Upgrade the .NET Agent for Windows - AppDynamics

2: Release Upgrade Checklist for .NET Agents - AppDynamics

3: REST API - AppDynamics

4: Configure the .NET Agent - AppDynamics

5: AppDynamics Application Performance Monitoring Platform - AppDynamics