Services managed by Ambari are defined in its stacks folder.

To define your own services and stacks to be managed by Ambari, follow the steps below to define your own services or stacks

A stack is a distribution of a set of services. Multiple versions of a stack can be defined, each with its own set of services. Stacks in Ambari are defined in  ambari-server/src/main/resources/stacks folder, which can be found at /var/lib/ambari-server/resources/stacks folder after install.

Services managed by a stack can be defined either in  ambari-server/src/main/resources/common-services or ambari-server/src/main/resources/stacks folders. These folders after install can be found at /var/lib/ambari-server/resources/common-services or /var/lib/ambari-server/resources/stacks folders respectively.

 Question: When do I define service in common-services vs. stacks folders?

One would define services in the common-services folder if there is possibility of the service being used in multiple stacks. For example, almost all stacks would need the HDFS service - so instead of redefining HDFS in each stack, the one defined in common-services is referenced from multiple stack-versions. Likewise, if a service is going to be contained in only one stack and never going to be shared, it can be defined in the stacks folder. Basically services defined in stacks folder are by used containment, whereas the ones defined in common-services are used by reference. 

Define Service

Components

Scripts

Command Order

Hooks

Configuration

Files

Alerts

Kerberos

Metrics

Widgets

Define Stack

Services

Repositories

Hooks

Configurations

Stack Advisor

Themes

Widgets