updated README.md

Author: Jacky Fan

typescript/api-gateway-async-lambda-invocation/README.md

@@ -1,14 +1,33 @@
-# Welcome to your CDK TypeScript project
+# API Gateway Asynchronous Lambda Invocation
 
-This is a blank project for CDK development with TypeScript.
+Sample architecture to process events asynchronously using API Gateway and Lambda and store result in DynamoDB.
 
-The `cdk.json` file tells the CDK Toolkit how to execute your app.
+## Architecture
+![architecture](./images/architecture.png)
 
-## Useful commands
+## Test:
+- `POST` curl command:
+```shell
+curl -X POST https://<API-ID>.execute-api.<REGION>.amazonaws.com/<stage>/job \
+    -H "X-Amz-Invocation-Type: Event" \
+    -H "Content-Type: application/json" \
+    -d '{}'
+```
 
-* `npm run build`   compile typescript to js
-* `npm run watch`   watch for changes and compile
-* `npm run test`    perform the jest unit tests
-* `npx cdk deploy`  deploy this stack to your default AWS account/region
-* `npx cdk diff`    compare deployed stack with current state
-* `npx cdk synth`   emits the synthesized CloudFormation template
+- `GET` curl command to get job details:
+```shell
+# jobId refers the output of the POST curl command.
+curl https://<API-ID>.execute-api.<REGION>.amazonaws.com/<stage>/job/<jobId>
+```
+
+
+```
+In Lambda non-proxy (custom) integration, the backend Lambda function is invoked synchronously by default.  
+This is the desired behavior for most REST API operations.  
+Some applications, however, require work to be performed asynchronously (as a batch operation or a long-latency operation), typically by a separate backend component.  
+In this case, the backend Lambda function is invoked asynchronously, and the front-end REST API method doesn't return the result.
+```
+
+### Reference:
+[1] Set up asynchronous invocation of the backend Lambda function  
+https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-integration-async.html