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Lab 1: Foundational API & Synchronous Lambda

Goal: Create the root REST API, deploy a simple Python Lambda function, and connect them using a Proxy Integration.

# 1. Create a basic Lambda function
cat <<EOF > api_handler.py
import json
def lambda_handler(event, context):
    return {"statusCode": 200, "body": json.dumps({"message": "Synchronous response from Lambda!"})}
EOF
zip function.zip api_handler.py

# 2. Create the IAM Execution Role and Lambda Function
ROLE_ARN=$(awslocal iam create-role --role-name APILambdaRole --assume-role-policy-document '{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Principal":{"Service":"lambda.amazonaws.com"},"Action":"sts:AssumeRole"}]}' --query 'Role.Arn' --output text)
ROLE_ARN=$(aws iam create-role --role-name APILambdaRole --assume-role-policy-document '{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Principal":{"Service":"lambda.amazonaws.com"},"Action":"sts:AssumeRole"}]}' --query 'Role.Arn' --output text)
LAMBDA_ARN=$(awslocal lambda create-function --function-name ApiCompute --runtime python3.9 --role $ROLE_ARN --handler api_handler.lambda_handler --zip-file fileb://function.zip --query 'FunctionArn' --output text)
LAMBDA_ARN=$(aws lambda create-function --function-name ApiCompute --runtime python3.9 --role $ROLE_ARN --handler api_handler.lambda_handler --zip-file fileb://function.zip --query 'FunctionArn' --output text)

# 3. Create the REST API and capture the Root Resource ID
API_ID=$(awslocal apigateway create-rest-api --name "EnterpriseAPI" --query 'id' --output text)
API_ID=$(aws apigateway create-rest-api --name "EnterpriseAPI" --query 'id' --output text)
PARENT_ID=$(awslocal apigateway get-resources --rest-api-id $API_ID --query 'items[0].id' --output text)
PARENT_ID=$(aws apigateway get-resources --rest-api-id $API_ID --query 'items[0].id' --output text)

# 4. Create a /sync resource and GET method
SYNC_ID=$(awslocal apigateway create-resource --rest-api-id $API_ID --parent-id $PARENT_ID --path-part "sync" --query 'id' --output text)
SYNC_ID=$(aws apigateway create-resource --rest-api-id $API_ID --parent-id $PARENT_ID --path-part "sync" --query 'id' --output text)
awslocal apigateway put-method --rest-api-id $API_ID --resource-id $SYNC_ID --http-method GET --authorization-type NONE
aws apigateway put-method --rest-api-id $API_ID --resource-id $SYNC_ID --http-method GET --authorization-type NONE

# 5. Connect the GET method to the Lambda function
awslocal apigateway put-integration \
  --rest-api-id $API_ID \
  --resource-id $SYNC_ID \
  --http-method GET \
  --type AWS_PROXY \
  --integration-http-method POST \
  --uri arn:aws:apigateway:us-east-1:lambda:path/2015-03-31/functions/$LAMBDA_ARN/invocations
aws apigateway put-integration \
  --rest-api-id $API_ID \
  --resource-id $SYNC_ID \
  --http-method GET \
  --type AWS_PROXY \
  --integration-http-method POST \
  --uri arn:aws:apigateway:us-east-1:lambda:path/2015-03-31/functions/$LAMBDA_ARN/invocations

🧠 Key Concepts & Importance

  • REST API: A collection of HTTP resources and methods that are integrated with backend HTTP endpoints, Lambda functions, or other AWS services.
  • Lambda Proxy Integration: The simplest way to integrate API Gateway with Lambda. API Gateway passes the entire incoming request to the Lambda function as-is, and the Lambda function must return a response in a specific format.
  • Resources & Methods: Resources represent paths (e.g., /sync), and methods represent HTTP verbs (e.g., GET, POST).
  • Integrations: Define how API Gateway communicates with the backend. For Lambda, the integration-http-method is always POST.

🛠️ Command Reference

  • iam create-role: Creates an IAM execution role for the Lambda function.
  • lambda create-function: Provisions the serverless compute resource.
  • apigateway create-rest-api: Initializes a new REST API container.
    • --name: The display name of the API.
  • apigateway get-resources: Retrieves the resources of an API (used here to find the root /).
  • apigateway create-resource: Creates a new path segment.
    • --path-part: The URL slug (e.g., sync).
  • apigateway put-method: Defines an HTTP method for a resource.
    • --http-method: The verb (e.g., GET).
    • --authorization-type: Security setting (e.g., NONE).
  • apigateway put-integration: Maps the API method to the backend.
    • --type: Integration type (e.g., AWS_PROXY).
    • --uri: The ARN of the backend service to trigger.

💡 Pro Tip: Using aws instead of awslocal

If you prefer using the standard aws CLI without the awslocal wrapper or repeating the --endpoint-url flag, you can configure a dedicated profile in your AWS config files.

1. Configure your Profile

Add the following to your ~/.aws/config file:

[profile localstack]
region = us-east-1
output = json
# This line redirects all commands for this profile to LocalStack
endpoint_url = http://localhost:4566

Add matching dummy credentials to your ~/.aws/credentials file:

[localstack]
aws_access_key_id = test
aws_secret_access_key = test

2. Use it in your Terminal

You can now run commands in two ways:

Option A: Pass the profile flag

aws iam create-user --user-name DevUser --profile localstack

Option B: Set an environment variable (Recommended) Set your profile once in your session, and all subsequent aws commands will automatically target LocalStack:

export AWS_PROFILE=localstack
aws iam create-user --user-name DevUser

Why this works

  • Precedence: The AWS CLI (v2) supports a global endpoint_url setting within a profile. When this is set, the CLI automatically redirects all API calls for that profile to your local container instead of the real AWS cloud.
  • Convenience: This allows you to use the standard documentation commands exactly as written, which is helpful if you are copy-pasting examples from AWS labs or tutorials.