AWS - Decouple configuration from code

Requirement

• Separate configuration from application code.
• Application code has to pickup any changes to configuration data immediately.

AWS AppConfig

• Feature of AWS Systems Manager service.
• AppConfig allows to quickly deploy configurations.
• Allows configuration formats like text / json / file from s3 etc.
• Applications that was using Tridion and migrating to AWS can make use of AWS AppConfig which is powerful than Tridion.
• AWS AppConfig can be used with applications hosted on Amazon EC2 instances, AWS Lambda, containers etc.

Creating configuration data in AWS AppConfig
This link walks through step by step creation and deployment of Configuration using AWS AppConfig.
To follow along this blog - use below settings while setup.

• Use Freeform Configuration profile type
• Application Name: BlogConfig
• Environment Name: prod
• Configuration Name: productRollout

Configuration data
Follow above link to deploy below JSON configuration data to AppConfig.

{
  "newProductRolloutFlag": true,  
  "newProductRolloutStates": ["IL","CA"]
}

How to access configuration data from AppConfig
Two ways - API from AWS SDK and Lambda Extension

AWS SDK
It's a two step process:
Without diving into extensive details, on a high level...

1. Establish configuration session using StartConfigurationSession API - this returns InitialConfigurationToken to be passed to the below API for first time.
2. GetLatestConfiguration API - this returns the latest configuration data from AppConfig along with NextPollConfigurationToken to be passed in subsequent call.

My personal choice is using AppConfig Lambda Extension - this is a performant and developer friendly way.

AppConfig Lambda extension
AWS has built a lambda extension for AppConfig - Below are the steps to add AppConfig Lambda Extension as a lambda layer in AWS console UI.
Goto AWS Lambda Service -> Add Lambda layer -> Choose a Layer -> AWS layers -> AWS-AppConfig-Extension -> Add the latest version shown.

Sample Code

//index.js (NodeJS runtime)
const http = require('http');
const params = process.env.APPCONFIG_PROFILE.split('/')
//Sample APPCONFIG_PROFILE value: "BlogConfig/prod/productRollout"
const AppConfigApplication = params [0]; //BlogConfig
const AppConfigEnvironment = params [1]; //prod
const AppConfigConfiguration = params [2] //productRollout

function getConfiguration(application, environment, configuration) {
    return new Promise((resolve, reject) => {
        const req = http.get(`http://localhost:2772/applications/${application}/environments/${environment}/configurations/${configuration}`, (res) => {
            if (res.statusCode < 200 || res.statusCode >= 300) {
                return reject(new Error('statusCode=' + res.statusCode));
            }
            var body = [];
            res.on('data', function(chunk) {
                body.push(chunk);
            });
            res.on('end', function() {
                resolve(Buffer.concat(body).toString());
            });
        });
        req.on('error', (e) => {
            reject(e.message);
        });
        req.end();
    });
}

exports.handler = async (event) => {
  try {
    const configData = await getConfiguration(AppConfigApplication, AppConfigEnvironment, AppConfigConfiguration);    
    const parsedConfigData = JSON.parse(configData);
    console.log(parsedConfigData);

    if(parsedConfigData.newProductRolloutFlag && parsedConfigData.newProductRolloutStates.includes("IL")) {
        console.log("Running newProduct feature");
        /*
        NEW PRODUCT ROLLOUT IMPLEMENTATION
        */
    }
  } catch (err) {
      console.error(err);
      return err;
  } 
}; 

Above example show cased the Seperation of Configuration data from source code as well as how Lambda immediately picks up changes to configuration data from AWS AppConfig.

Image by Gino Crescoli from Pixabay