This project contains Python source code and supporting files for a serverless application that you can deploy with the SAM CLI and that uses CodeDeploy and Lambda traffic shifting for deployment. This is a demo for my immutable infrastructure talk.
AWS Lambda and AWS CodeDeploy make it possible to automatically shift incoming traffic between two AWS Lambda function versions based on a preconfigured rollout strategy. This feature allows you to gradually shift traffic to the new version of your AWS Lambda function. If there are any issues with the new code, it can quickly rollback without affecting your application and your customers.
This project includes the following files and folders.
- hello_world - Code for the application's Lambda function.
- pre-traffic-hook - Code for the pretraffic hook used by CodeDeploy to monitor the deployment of new Lambda functions.
- 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.
The application uses several AWS resources, including Lambda functions, an API Gateway API, AWS CloudWatch alarms, and AWS CodeDeploy. 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.
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.
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
capabilitiesmust be provided. If permission isn't provided through this prompt, to deploy this example you must explicitly pass
--capabilities CAPABILITY_IAMto the
- 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 deploywithout 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.
sam-app1$ sam build --use-container
The SAM CLI installs dependencies defined in
hello_world/requirements.txt, creates a deployment package, and saves it in the
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.
sam-app1$ 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.
sam-app1$ sam local start-api sam-app1$ 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 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.
sam-app1$ sam logs -n HelloWorldFunction --stack-name sam-app1 --tail
You can find more information and examples about filtering Lambda function logs in the SAM CLI Documentation.
Tests are defined in the
tests folder in this project. Use PIP to install the pytest and run unit tests.
sam-app1$ pip install pytest pytest-mock --user sam-app1$ python -m pytest tests/ -v
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 sam-app1
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