This topic describes the basic elements of the AppDynamics model.
Before deploying AppDynamics, also see Mapping Application Services to the AppDynamics Model.
An AppDynamics business application models all components or modules in an application environment that provide a complete set of functionality. Think of it as all the web applications, databases, and services that interact or "talk" to each other or to a shared component. When web applications, databases, and services interact, AppDynamics can correlate their activities to provide useful and interesting performance data.
AppDynamics lets you monitor multiple business applications, though it does not correlate events between them.
Because a single node belongs to a single business application, you can also think of a business application as a kind of namespace for all your nodes. See Nodes.
Business applications contain tiers, and tiers contain nodes.
A tier represents a key module in an application environment, such as a website or processing application or a virtual machine. Tiers help you logically organize and manage your business application so that you can scale multiple nodes, partition metrics, define performance thresholds, and respond to anomalies. The metrics from one tier tell a different story than those from another tier; AppDynamics helps you define different policies and processes for each tier. A tier can belong to only one business application.
A tier is composed of one node or a group of nodes. For example, in the Acme sample application the Inventory tier has one node whereas the E-Commerce tier has 2 nodes.
Nodes grouped into a tier may have redundant functionality or may not. An example of a multi-node tier with redundant nodes is when you have a set of clustered application servers or services. An example of a multi-node tier with different nodes is when you have a set of services that do not interact with each other though you want to roll up their performance metrics together.
Keep in mind that an environment can have similar nodes that are used by different applications, so similar nodes should not always belong to the same tier. An example is a complex environment that has two HTTP web servers that serve two separate applications.
Business applications contain tiers. The traffic in a business application flows between tiers. This flow is represented in AppDynamics flow maps along with performance data for the traffic. There is always a tier that is the starting point for a Business Transaction, indicated by a Start label on the flow map.
A node is the basic unit of processing that AppDynamics monitors. By definition a node is instrumented by an AppDynamics agent, either an app agent or machine agent or both. App agents are installed on:
- Windows .NET applications (IIS, executables, or services)
- PHP Runtime Instances
- Node.js processes
Machine agents are installed on virtual or physical machine operating systems.
Nodes belong to tiers. An app agent node cannot belong to more than one tier. A machine agent cannot belong to more than one tier; however you can install more than one machine agent on a machine.