Lab: Automating Deployment Testing with AWS CI/CD and SAM

In this lab, you will learn how to automate the testing of serverless applications. You will use the AWS Serverless Application Model (SAM) to define your infrastructure and AWS CodeBuild to execute automated unit and integration tests as part of a continuous delivery pipeline.

Prerequisites

Before starting this lab, ensure you have the following:

An AWS Account with administrative access.
AWS CLI installed and configured with your credentials.
AWS SAM CLI installed on your local machine.
Basic knowledge of Python (for the Lambda function) and YAML (for configuration).
Git installed locally.

Learning Objectives

By the end of this lab, you will be able to:

Create application test events and JSON payloads for AWS Lambda.
Implement and deploy Infrastructure as Code (IaC) templates using AWS SAM.
Configure AWS CodeBuild to run automated tests during the build phase.
Differentiate between deployment environments (stages) in Amazon API Gateway.

Architecture Overview

The following diagram illustrates the automated testing and deployment workflow you will build:

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The Testing Lifecycle

The cost of fixing bugs increases exponentially as they move toward production. This lab focuses on catching bugs in the "Build" and "Staging" phases.

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Step-by-Step Instructions

Step 1: Initialize the SAM Project

We will start with a basic "Hello World" application using the AWS SAM CLI.

bash

sam init --name brainybee-testing-lab --runtime python3.9 --app-template hello-world --package-type Zip
cd brainybee-testing-lab

[!TIP] This command creates a directory structure containing a template.yaml file (IaC) and a hello_world folder for your Lambda code.

Step 2: Create an Automated Unit Test

Navigate to the tests/unit folder. We will ensure the Lambda function returns a 200 OK status code.

bash

# Edit tests/unit/test_handler.py to include a basic assertion
cat <<EOF > tests/unit/test_handler.py
import json
from hello_world import app

def test_lambda_handler():
    event = {"body": "test"}
    ret = app.lambda_handler(event, "")
    assert ret["statusCode"] == 200
    assert "message" in ret["body"]
EOF

Step 3: Configure the Buildspec for Testing

CodeBuild requires a buildspec.yml file to know how to run your tests. Create this file in the root directory.

bash

cat <<EOF > buildspec.yml
version: 0.2
phases:
  install:
    runtime-versions:
      python: 3.9
    commands:
      - pip install -r hello_world/requirements.txt
      - pip install pytest
  pre_build:
    commands:
      - echo Running unit tests...
      - pytest tests/unit/test_handler.py
  build:
    commands:
      - echo Packaging SAM application...
      - sam package --output-template-file packaged.yaml --s3-bucket <YOUR_S3_BUCKET_NAME>
artifacts:
  files:
    - packaged.yaml
EOF

▶Console alternative

Navigate to

CodeBuild

in the AWS Console. 2. Create a

Build Project

. 3. Under

Buildspec

, select "Insert build commands" or point it to the file in your repository.

Step 4: Define Environments in SAM

Update your template.yaml to include a Stage parameter. This allows you to differentiate between dev, test, and prod stages in API Gateway.

yaml

Parameters:
  Stage:
    Type: String
    Default: dev

Resources:
  HelloWorldFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: hello_world/
      Handler: app.lambda_handler
      Runtime: python3.9
      Events:
        HelloWorld:
          Type: Api
          Properties:
            Path: /hello
            Method: get
            RestApiId: !Ref MyApi

  MyApi:
    Type: AWS::Serverless::Api
    Properties:
      StageName: !Ref Stage

Checkpoints

Checkpoint 1: Local Test Execution

Run your tests locally to ensure the logic is sound before committing to the cloud.

bash

pytest tests/unit/test_handler.py

Expected Result: 1 passed in 0.01s.

Checkpoint 2: Validate SAM Template

bash

sam validate

Expected Result: template.yaml is a valid SAM Template.

Clean-Up / Teardown

[!WARNING] Failure to delete these resources may result in unexpected charges to your AWS account.

Delete the SAM Stack:
bash
sam delete --stack-name brainybee-testing-lab
Delete the S3 Bucket (if created for artifacts):
bash
aws s3 rb s3://<YOUR_S3_BUCKET_NAME> --force
Delete CodeBuild/CodePipeline projects via the console or CLI if you created them manually.

Troubleshooting

Error	Possible Cause	Fix
`sam package` fails	Missing S3 bucket or permissions	Ensure bucket exists and CLI has `s3:PutObject` permissions
`pytest` not found	Buildspec install phase failed	Check python version and pip installation steps in `buildspec.yml`
Deployment fails	IAM role for CloudFormation lacks permissions	Ensure the execution role has permissions to create Lambda and API Gateway

Stretch Challenge

Implement a Lambda Alias for Traffic Shifting: Modify your template.yaml to include an AutoPublishAlias: live and a DeploymentPreference type like Canary10Percent5Minutes. This automates the "test in production" phase by slowly shifting traffic and rolling back if CloudWatch Alarms trigger.

Cost Estimate

Service	Estimated Cost (Free Tier)	Estimated Cost (Beyond Free Tier)
AWS Lambda	First 1M requests free	$0.20 per 1M requests
AWS CodeBuild	100 build minutes/mo free	~$0.005 per minute
Amazon S3	5GB Standard storage free	$0.023 per GB
Total	$0.00	< $0.10 for this lab

Concept Review

Concept	Description	Real-World Example
Unit Test	Testing a single function in isolation.	Mocking a DB call to see if your Lambda processes the JSON correctly.
Integration Test	Testing the interaction between services.	Deploying to a `staging` endpoint and sending a real HTTP request to verify API Gateway + Lambda.
SAM Template	An extension of CloudFormation for serverless.	Defining your entire backend (API, DB, Auth) in one 100-line YAML file.
Buildspec	Instructions for the build server.	Compiling code and running `npm test` before deployment.