Serverless Application Using AWS S3, AWS APIGateway and AWS Lambda — A CLI Method

There are so many GUI examples on the net, here is the CLI way!

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Above diagram is what we will be building. AWS S3 bucket will be configured to work as a static website. The web page will have an AJAX call to the Lambda function via the APIGateway endpoint.

Let us get started

Create A Lambda Function

Policy for the role to be used by the Lambda function

"Version": "2012-10-17",
"Statement": [
"Effect": "Allow",
"Principal": {
"Service": ""
"Action": "sts:AssumeRole"

Create a role

aws iam create-role --role-name sree-lambda --assume-role-policy-document file://policy.json

Python function

print "Starting..\n"
def sree_handler(event, context):
ans = str(kg) + " Kgs is " + str(round(lb, 2)) + " lbs\n"
print ans
return ans

Zip the function


Create the Lambda Function

aws lambda create-function --function-name sree-py1 --zip-file fileb:// --handler sree_fn.sree_handler --runtime python2.7 --role arn:aws:iam::111111111:role/sree-lambda

Test the function

aws lambda invoke --function-name sree-py1 --payload '{"Kg":"100"}' results
"StatusCode": 200,
"ExecutedVersion": "$LATEST"
cat results
"100 Kgs is 220.46 lbs\n"

Create APIGateway Endpoint


api_id=$(aws apigateway create-rest-api --name 'SreeDemo' --description 'My CLI Demo' --query id --output text);echo $api_idroot_id=$(aws apigateway get-resources --rest-api-id $api_id --query items[0].id --output text)

Create Resource

id=$(aws apigateway create-resource --rest-api-id $api_id  --path-part kg-to-lb \
--parent-id $root_id --query id --output text)

Create a GET method with Query String Parameter

aws apigateway put-method --rest-api-id $api_id --resource-id $root_id \
--http-method GET --authorization-type NONE \
--no-api-key-required \
--request-parameters "{ \"\": false }"

Add Method Response

aws apigateway put-method-response --rest-api-id $api_id \
--resource-id $root_id --http-method GET \
--status-code 200 --response-models "{\"application/json\": \"Empty\"}"

Get the Lambda Function ARN and Assemble the URI

fn_arn=$(aws lambda get-function --function-name sree-py1 --query Configuration.FunctionArn --output text)uri=arn:aws:apigateway:us-west-2:lambda:path/2015-03-31/functions/$fn_arn/invocations

Add Integration to connect APIGateway and Lambda

Here we also pass the mapping from our query string to JSON needed for Lambda function.

aws apigateway put-integration --rest-api-id $api_id --resource-id $root_id \
--type AWS \
--http-method GET \
--integration-http-method POST \
--uri $uri \
--request-templates "{ \"application/json\": \"{\\n\\\"Kg\\\": \\\"\$input.params('kg')\\\"\\n}\" }"

Add Permission to Lambda to Allow APIGateway Calls

aws lambda add-permission --function-name sree-py1 \
--statement-id apigateway-test-3 --action lambda:InvokeFunction \
--principal \
--source-arn "arn:aws:execute-api:us-west-2:111111111:$api_id/*/GET/"

Add Integration response.

Notice the CORS header being added here. This is required for this endpoint to allow being called by other websites.

aws apigateway put-integration-response --rest-api-id $api_id \
--resource-id $root_id --http-method GET \
--status-code 200 \
--content-handling CONVERT_TO_TEXT \
--response-parameters "{\"method.response.header.Access-Control-Allow-Origin\": \"'*'\"}"
"statusCode": "200",
"responseParameters": {
"method.response.header.Access-Control-Allow-Origin": "'*'"
"contentHandling": "CONVERT_TO_TEXT"

Create a Deployment / Stage

aws apigateway get-stages --rest-api-id $api_id
"item": []
aws apigateway get-deployments --rest-api-id $api_id
"items": []
aws apigateway create-deployment --rest-api-id $api_id --stage-name stage1
"id": "snks4p",
"createdDate": 1542957908
aws apigateway get-stages --rest-api-id $api_id
"item": [
"deploymentId": "snks4p",
"stageName": "stage1",
"cacheClusterEnabled": false,
"cacheClusterStatus": "NOT_AVAILABLE",
"methodSettings": {},
"createdDate": 1542957908,
"lastUpdatedDate": 1542957908
aws apigateway get-deployments --rest-api-id $api_id
"items": [
"id": "snks4p",
"createdDate": 1542957908

Test the APIGateway endpoint

curl https://$
"22 Kgs is 48.5 lbs\n"

Create a Serverless Web Application

Make the S3 Bucket

aws s3 mb --region $sree_BUCKET_REGION s3://$sree_BUCKET_NAME

Public Read Bucket Policy

cat > s3-www-policy.json <<EOT
"Principal": "*",
aws s3api put-bucket-policy --bucket $sree_BUCKET_NAME --policy file://s3-www-policy.json

Website Options

cat > s3.www.json <<EOT
"IndexDocument": {
"Suffix": "index.html"
"ErrorDocument": {
"Key": "404.html"
"RoutingRules": [
"Redirect": {
"ReplaceKeyWith": "index.html"
"Condition": {
"KeyPrefixEquals": "/"
aws s3api put-bucket-website --bucket $sree_BUCKET_NAME --website-configuration file://s3.www.json

Index page

<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8">
<title>Serverless Website</title>
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="" rel="stylesheet">
<script src=""></script>
<!--[if lt IE 9]>
<script src=""></script>
<script src=""></script>
<div class="container">
<h1>Serverless Website</h1>
<h2>Kgs to Lbs Converter Using AWS APIGateway and Lambda</h2>
<form class="form-inline">
<div class="form-group mx-sm-3 mb-2">
<label for="inputPassword2" class="sr-only">Password</label>
<input type="text" class="form-control" id="kg" placeholder="1" value="1">
<button type="submit" onClick="conv();return false;" class="btn btn-primary mb-2">Convert to Lbs</button>
<div id="res"><h1>
<script src=""></script>
<script type="text/javascript">
function conv(){
$("#res").load(""+$("#kg").val(),function() {

var s=$("#res").html();
s=s.replace('"', "")
s=s.replace('"', "")
s=s.replace('\\n', "")
alert( "Lambda function executed succesfully!" );

After uploading the above index we are ready to test the S3 website!

Final Test

Thanks for your time. Do follow for more such end to end demos.

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