Reuse code and resources using nested applications in AWS SAM

A serverless application can include one or more nested applications. A nested application is a part of a larger application and can be packaged and deployed either as a stand-alone artifact or as a component of the larger application. Nested applications allow you to turn frequently used code and into its own application that can then be reused across a larger serverless application or multiple serverless applications.

As your serverless architectures grows, common patterns typically emerge in which the same components are defined in multiple application templates. Nested applications allow you to reuse common code, functionality, resources, and configurations in separate AWS SAM templates, allowing you to only maintain code from a single source. This reduces duplicated code and configurations. Additionally, this modular approach streamlines development, enhances code organization, and facilitates consistency across serverless applications. With nested applications, you can stay more focused on the business logic that's unique to your application.

To define a nested application in your serverless application, use the AWS::Serverless::Application resource type.

You can define nested applications from the following two sources:

See the following sections for details on how to use AWS SAM to define both of these types of nested applications in your serverless application.

Defining a nested application from the AWS Serverless Application Repository

You can define nested applications by using applications that are available in the AWS Serverless Application Repository. You can also store and distribute applications that contain nested applications using the AWS Serverless Application Repository. To review details of a nested application in the AWS Serverless Application Repository, you can use the AWS SDK, the AWS CLI, or the Lambda console.

To define an application that's hosted in the AWS Serverless Application Repository in your serverless application's AWS SAM template, use the Copy as SAM Resource button on the detail page of every AWS Serverless Application Repository application. To do this, follow these steps:

The following is an example SAM template section for a nested application that's hosted in the AWS Serverless Application Repository:

Transform: AWS::Serverless-2016-10-31

Resources:
  applicationaliasname:
    Type: AWS::Serverless::Application
    Properties:
      Location:
        ApplicationId: arn:aws:serverlessrepo:us-east-1:123456789012:applications/application-alias-name
        SemanticVersion: 1.0.0
      Parameters:
        # Optional parameter that can have default value overridden
        # ParameterName1: 15 # Uncomment to override default value
        # Required parameter that needs value to be provided
        ParameterName2: YOUR_VALUE

If there are no required parameter settings, you can omit the Parameters: section of the template.

Defining a nested application from the local file system

You can define nested applications by using applications that are stored on your local file system. You do this by specifying the path to the AWS SAM template file that's stored on your local file system.

The following is an example SAM template section for a nested local application:

Transform: AWS::Serverless-2016-10-31

Resources:
  applicationaliasname:
    Type: AWS::Serverless::Application
    Properties:
      Location: ../my-other-app/template.yaml
      Parameters:
        # Optional parameter that can have default value overridden
        # ParameterName1: 15 # Uncomment to override default value
        # Required parameter that needs value to be provided
        ParameterName2: YOUR_VALUE

If there are no parameter settings, you can omit the Parameters: section of the template.

Deploying nested applications

You can deploy your nested application by using the AWS SAM CLI command sam deploy. For more details, see Deploy your application and resources with AWS SAM.