Summary

This example uses tracer, metrics,and logger features, includes all environment variables that can be used, and demonstrates how to explicitly disable tracing while running unit tests - That is not necessary when running within SAM CLI as it detects the local env automatically.

Quick commands

Build: sam build --use-container
Invoke locally: sam local invoke HelloWorldFunction --event events/event.json
Deploy: sam deploy --guided
Unit Tests: We recommend proceeding with the following commands in a virtual environment
- Install deps: pip install -r hello_world/requirements.txt && pip install -r requirements-dev.txt
- Run tests with namespace and service set, and tracing disabled
  - POWERTOOLS_METRICS_NAMESPACE="Example" POWERTOOLS_SERVICE_NAME="Example" POWERTOOLS_TRACE_DISABLED=1 python -m pytest
  - These are necessary because app.py initializes them in the global scope, since both Tracer and Metrics will be initialized and configured during import time. For unit tests, we could always patch and explicitly config but env vars do just fine for this example.

Example code

This project contains source code and supporting files for a serverless application that you can deploy with the SAM CLI. It includes the following files and folders.

hello_world - Code for the application's Lambda function.
events - Invocation events that you can use to invoke the function.
tests - Unit tests for the application code.
template.yaml - A template that defines the application's AWS resources.
requirements-dev.txt - Dev dependencies to run unit tests successfully

The application uses several AWS resources, including Lambda functions and an API Gateway API. These resources are defined in the template.yaml file in this project. You can update the template to add AWS resources through the same deployment process that updates your application code.

If you prefer to use an integrated development environment (IDE) to build and test your application, you can use the AWS Toolkit. The AWS Toolkit is an open source plug-in for popular IDEs that uses the SAM CLI to build and deploy serverless applications on AWS. The AWS Toolkit also adds a simplified step-through debugging experience for Lambda function code. See the following links to get started.

Deploy the sample application

The Serverless Application Model Command Line Interface (SAM CLI) is an extension of the AWS CLI that adds functionality for building and testing Lambda applications. It uses Docker to run your functions in an Amazon Linux environment that matches Lambda. It can also emulate your application's build environment and API.

To use the SAM CLI, you need the following tools.

SAM CLI - Install the SAM CLI
Python 3 installed
Docker - Install Docker community edition

To build and deploy your application for the first time, run the following in your shell:

sam build --use-container
sam deploy --guided

The first command will build the source of your application. The second command will package and deploy your application to AWS, with a series of prompts:

Stack Name: The name of the stack to deploy to CloudFormation. This should be unique to your account and region, and a good starting point would be something matching your project name.
AWS Region: The AWS region you want to deploy your app to.
Confirm changes before deploy: If set to yes, any change sets will be shown to you before execution for manual review. If set to no, the AWS SAM CLI will automatically deploy application changes.
Allow SAM CLI IAM role creation: Many AWS SAM templates, including this example, create AWS IAM roles required for the AWS Lambda function(s) included to access AWS services. By default, these are scoped down to minimum required permissions. To deploy an AWS CloudFormation stack which creates or modified IAM roles, the CAPABILITY_IAM value for capabilities must be provided. If permission isn't provided through this prompt, to deploy this example you must explicitly pass --capabilities CAPABILITY_IAM to the sam deploy command.
Save arguments to samconfig.toml: If set to yes, your choices will be saved to a configuration file inside the project, so that in the future you can just re-run sam deploy without parameters to deploy changes to your application.

You can find your API Gateway Endpoint URL in the output values displayed after deployment.

Use the SAM CLI to build and test locally

Build your application with the sam build --use-container command.

example$ sam build --use-container

The SAM CLI installs dependencies defined in hello_world/requirements.txt, creates a deployment package, and saves it in the .aws-sam/build folder.

Test a single function by invoking it directly with a test event. An event is a JSON document that represents the input that the function receives from the event source. Test events are included in the events folder in this project.

Run functions locally and invoke them with the sam local invoke command.

example$ sam local invoke HelloWorldFunction --event events/event.json

The SAM CLI can also emulate your application's API. Use the sam local start-api to run the API locally on port 3000.

example$ sam local start-api
example$ curl http://localhost:3000/

The SAM CLI reads the application template to determine the API's routes and the functions that they invoke. The Events property on each function's definition includes the route and method for each path.

      Events:
        HelloWorld:
          Type: Api
          Properties:
            Path: /hello
            Method: get

Add a resource to your application

The application template uses AWS Serverless Application Model (AWS SAM) to define application resources. AWS SAM is an extension of AWS CloudFormation with a simpler syntax for configuring common serverless application resources such as functions, triggers, and APIs. For resources not included in the SAM specification, you can use standard AWS CloudFormation resource types.

Fetch, tail, and filter Lambda function logs

To simplify troubleshooting, SAM CLI has a command called sam logs. sam logs lets you fetch logs generated by your deployed Lambda function from the command line. In addition to printing the logs on the terminal, this command has several nifty features to help you quickly find the bug.

NOTE: This command works for all AWS Lambda functions; not just the ones you deploy using SAM.

example$ sam logs -n HelloWorldFunction --stack-name example --tail

You can find more information and examples about filtering Lambda function logs in the SAM CLI Documentation.

Unit tests

Tests are defined in the tests folder in this project. Use PIP to install the deps and run unit tests.

example$ pip install -r hello_world/requirements.txt
example$ pip install -r requirements-dev.txt
example$ pytest -v

Cleanup

To delete the sample application that you created, use the AWS CLI. Assuming you used your project name for the stack name, you can run the following:

aws cloudformation delete-stack --stack-name example

Resources

See the AWS SAM developer guide for an introduction to SAM specification, the SAM CLI, and serverless application concepts.

Next, you can use AWS Serverless Application Repository to deploy ready to use Apps that go beyond hello world samples and learn how authors developed their applications: AWS Serverless Application Repository main page