There are four main types of agents used in AppDynamics.

1. **End User Agents** - for web and mobile
(android and iOS) that measure
business transactions for end user
experience
2. **Application Server Agents** - that reside in your business logic tier
and see the code executed

3. **Machine Agents** - Monitor your infrastructure and power integration
with other software and/or support
run book automation.

4. **Database Agents** - Provide visibility into the database in the
context of business transactions, but is not meant to replace database
tools.

The agents that are available for your application are:

1. Java
2. .NET
3. PHP
4. Node JS

You cant monitor the agents without the key piece of software....the Controller. You will want to install one agent on each node in your environment. Once that is done the agents automatically discover all the nodes and Tiers within your application and displays it to the Controller via the flow map, giving you an accurate representation of your application.