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AWS SAM Nested Applications with single package.json

This is an example of using AWS SAM with nested applications sharing a single package.json.

We have a Rest API TypeScript application (apps/rest-api/handlers) that uses dependencies from the root package.json.

We have a DynamoDB Stream with a TypeScript lambda consumer (apps/dynamodb/handlers) that uses dependencies from the root package.json.

Any application can define its own TypeScript Lambda and use the root package.json.

The parent AWS SAM application is defined in ./template.yaml and child applications are defined in ./apps/*/template.yaml.

Benefits

This enables the developer to use a single package.json and share it across the entire application. esbuild will be packing each lambda handler bundling the correct dependencies imported by each handler.

Drawback

You need to define --base-dir for every AWS SAM CLI command that have it as an option.

When using sam sync chaging the source code of one lambda with sync all lambdas of that stack. For example, apps/rest-api is a stack with 2 lambdas. If you change the source code of one lambda, all 2 lambdas will be synced.

Conventions on how to use

We have a few conventions:

  1. The package.json is located in the root of the project
  2. The CodeUri of any lambda is always ./
  3. Definitions for lambda handlers entry points are defined using the full relative path of the project root
  4. When running sam build from the root of the project, we need to define --base-dir . to make sure that esbuild will be able to find the package.json in the root of the project and resolve all relative paths correctly

For example:

Resources:
    GetBooksFunction:
        Type: AWS::Serverless::Function
        Properties:
            CodeUri: ./
            Handler: get-books.handler
            # ...
        Metadata:
            # ...
            BuildProperties:
                # ...
                EntryPoints:
                    - apps/rest-api/handlers/get-books.ts

Important: The --base-dir must be defined for every AWS SAM CLI command that have it as an option.

Deploying to AWS

You can use any AWS SAM CLI command, make sure you include --base-dir . when running from the root of the project.

With sync:

sam sync --base-dir .

With deploy:

sam build --base-dir .
sam deploy

Running locally

You can run it locally as you would normally do with AWS SAM CLI.

With local start-api:

sam build --base-dir .
sam local start-api

With local invoke:

sam build --base-dir .
sam local invoke StackRestApi/GetCategoriesFunction