Testing AWS SAM Local App Config for Python Lambda with Local Development Mode

AWS Serverless Application Model (SAM) allows developers to build and test serverless applications locally. When working with AWS App Config and Python Lambda functions, it is crucial to understand how to test the setup locally. This article will explain the process of testing an AWS SAM local App Config Python Lambda in local development mode.

Prerequisites

To get started, ensure you have the following tools installed:

• Python 3.8 or later
• AWS CLI
• AWS SAM CLI
• Docker

Setting up an AWS App Config Environment

The first step is to set up an AWS App Config environment in your AWS Management Console. Follow the steps in the documentation to create an application and environment:

AWS AppConfig Getting Started Guide

Creating a Python Lambda Function

Next, create a Python Lambda function that will receive configuration data from App Config. Here's an example of a simple Lambda function:

 import json

 def lambda_handler(event, context):
 configuration = event['configuration']
 monitored_data = configuration['monitoredData']
 print('Received monitored data:', monitored_data)
 return {
 'statusCode': 200,
 'body': json.dumps('Configuration applied successfully!')
 }
 

Configuring the AWS SAM Template

To integrate your Lambda function with App Config, you need to update your AWS SAM template. Here's an example of a template.yaml file:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: AWS Serverless Application
Resources:
 MyFunction:
 Type: AWS::Serverless::Function
 Properties:
 Handler: app.lambda_handler
 Runtime: python3.8
 Events:
 AppConfigEvent:
 Type: AWS::AppConfig::Configuration
 Properties:
 ApplicationName: !Ref MyApplication
 ConfigurationName: !Ref MyConfiguration
 

Replace MyApplication and MyConfiguration with the names of your AWS AppConfig application and configuration.

Testing the Lambda Function Locally

Use the following command to test your Lambda function locally. Replace MyApplication and MyConfiguration with the names of your AWS AppConfig application and configuration.

 sam local invoke MyFunction --event event.json
 

Here's an example event.json file:

 {
 "configuration": {
 "monitoredData": {
 "exampleKey": "exampleValue"
 }
 }
 }
 

Setting up the AppConfig Agent and Lambda Extension

To enable local development mode for App Config, follow these steps:

1. Create the AppConfig agent manifest file with the following content:

 {
 "name": "appconfig-deploy",
 "version": "1.0.0",
 "config": {
 "aws": {
 "region": <your-region>
 }
 }
 }
 

Replace <your-region> with your AWS region.

2. Add the following to your .aws/sam/config.toml file:

 [dev.appconfig]
 agent_manifest = "appconfig-agent-manifest.json"
 extension_config = "appconfig-extension-config.json"
 

Create an empty appconfig-extension-config.json file.

Testing the Agent and Extension in Local Development Mode

After setting up the agent and extension for local development mode, use the following command to test the Lambda function:

 sam local start-api
 

You can now update and monitor the Lambda function using the AppConfig application. The changes will be reflected in your local development environment.

In this article, we have discussed how to test an AWS SAM local App Config Python Lambda in local development mode. By following the steps outlined, you can test and iterate on your serverless applications locally with App Config.

References

• AWS AppConfig Retrieving Configuration Values

• AWS SAM AWS AppConfig Integration

• AWS AppConfig Working with Agents

• SAM CLI Local API Reference