Using nested applications

A serverless application can include one or more nested applications. You can deploy a nested application as a stand-alone artifact or as a component of a larger application.

As serverless architectures grow, common patterns emerge in which the same components are defined in multiple application templates. You can now separate out common patterns as dedicated applications, and then nest them as part of new or existing application templates. 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:

• An AWS Serverless Application Repository application – You can define nested applications by using applications that are available to your account in the AWS Serverless Application Repository. These can be private applications in your account, applications that are privately shared with your account, or applications that are publicly shared in the AWS Serverless Application Repository. For more information about the different deployment permissions levels, see Application Deployment Permissions and Publishing Applications in the AWS Serverless Application Repository Developer Guide.

• A local application – You can define nested applications by using applications that are stored on your local file system.

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.

Note

The maximum number of applications that can be nested in a serverless application is 200.

The maximum number of parameters a nested application can have is 60.

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:

1. Make sure that you're signed in to the AWS Management Console.

2. Find the application that you want to nest in the AWS Serverless Application Repository by using the steps in the Browsing, Searching, and Deploying Applications section of the AWS Serverless Application Repository Developer Guide.

3. Choose the Copy as SAM Resource button. The SAM template section for the application that you're viewing is now in your clipboard.

4. Paste the SAM template section into the Resources: section of the SAM template file for the application that you want to nest in this application.

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.

Important

Applications that contain nested applications hosted in the AWS Serverless Application Repository inherit the nested applications' sharing restrictions.

For example, suppose an application is publicly shared, but it contains a nested application that's only privately shared with the AWS account that created the parent application. In this case, if your AWS account doesn't have permission to deploy the nested application, you aren't able to deploy the parent application. For more information about permissions to deploy applications, see Application Deployment Permissions and Publishing Applications in the AWS Serverless Application Repository Developer Guide.

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 Deploying serverless applications.

Note

When you deploy an application that contains nested applications, you must acknowledge that. You do this by passing CAPABILITY_AUTO_EXPAND to the CreateCloudFormationChangeSet API,or using the aws serverlessrepo create-cloud-formation-change-set AWS CLI command.

For more information about acknowledging nested applications, see Acknowledging IAM Roles, Resource Policies, and Nested Applications when Deploying Applications in the AWS Serverless Application Repository Developer Guide.