Any applications, patches, and updates that we would like to apply to our instances within a layer of a stack are represented as apps. An app needs to be delivered from a repository such as an S3 bucket or Git. Once we have published an app in the repository, it can be applied to a layer. Once an app has been assigned to a layer, each instance that becomes a member of a layer will have all of the layers apps automatically installed.

Each app is composed of the following sections:

• Settings: This represents the name of the app and its document structure.
• Application Source: This represents the sources for the installation of applications, such as repositories and bundles that need to be made accessible to the instances that are managed by OpsWorks.
• Data Sources: These represent databases that need to be attached to the application if required.
• Environment Variables: These represent application-specific variables that can be passed into the instance upon deployment of the application.
• Domain and SSL Settings: These represent domain and SSL certificates that are being configured on the instance.