What is Lambda@Edge & How to detect a simple Crawler BOT using AWS Lambda@Edge in Node JS
About Lamda@Edge
Lambda@Edge provides a way to run the Lambda functions to customize content that CloudFront delivers. Currently, it supports only two languages (Node.js & Python).
It executes the functions in AWS locations closer to the viewer. The functions run in response to CloudFront events.
You can use Lambda functions to change CloudFront requests and responses at the following points:
- viewer request: We can change the request before CloudFront receives a request from a viewer
- origin request: We can change the request after CloudFront forwards the request to the origin
- origin response: We can change the response after CloudFront receives the response from the origin
- viewer response: We can change the response before CloudFront forwards the response to the viewer
View the full AWS article here
Difference between Lambda and Lambda@Edge
- Lambda Function executes based on certain triggers
- Lambda@Edge is a Lambda function that is executed in response to CloudFront events.
How to create the Lambda@Edge and associate with CDN
Note: Lambda@Edge should be created in the us-east-1 (N. Virginia) region only. It will automatically replicate to all the edge locations.
Step 1: Go to the Lambda service and select the region to us-east-1 and create a Lambda function and put the below code into the lambda event handler.
'use strict';const regex = /aolbuild|baidu|bingbot|bingpreview|msnbot|duckduckgo|adsbot-google|googlebot|mediapartners-google|teoma|slurp|yandex|bot|crawl|spider/g;exports.handler = (event, context, callback) => {
console.log('Event: ' + JSON.stringify(event));
const request = event.Records[0].cf.request;
const user_agent = request['headers']['user-agent'][0]['value'].toLowerCase();
if(user_agent !== undefined) {
const found = user_agent.match(regex);
request['headers']['is-crawler'] = [
{
key: 'is-crawler',
value: `${found !== null}`
}
]
}console.log('Request: ' + JSON.stringify(request));
callback(null, request);
};
Step 2: Go to the “configuration” tab of the lambda function and select the “Permissions” tab at the left. Please click on the role.
Step3: Once you redirected to the IAM after clicking the Lambda role, Please select the “trust relationship” tab and then edit the “trust relationship”.
Paste the below statement and update the trust policy.
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"Service": [
"lambda.amazonaws.com",
"edgelambda.amazonaws.com"
]
},
"Action": "sts:AssumeRole"
}
]
}Step 4: You can not add the CDN trigger with the $LATEST version of the lambda function, for adding the trigger we need to create the version. To create a version you need to click on the “version” tab in the Lambda and click on the “Publish new version”
Step 5: once created the version please add now the CDN as a trigger. I assume that you have already created the CloudFront. Select the CloudFront into distribution and confirm deploy to Lambda@Edge.
Step 6: Validate the Lambda@Edge is correctly associated with your CDN. Go to Cloudfront service > behavior tab > Select the checkbox and click edit > and scroll to the bottom.
We are done with all settings. Let wait for some time to replicate your function to all the edge locations.
How to check the Lambda@Edge Logs
When you check for the log files, be aware that log files are stored in the Region closest to the location where the function is executed. This means, if you visit a website from, for example, India, you must change the Region to view the CloudWatch Logs for the Mumbai(ap-south-1) Region.
Please read the AWS article for it.
How to delete the Lamda@Edge function
You can not delete the Lambda@Edge directly from the lambda functions page because it is already replicated into all edge locations. If you try to delete it, you will face the below issue.
To delete the Lambda@Edge, you need to remove the association from Cloudfront first using the “cross” button available in front of the association . Please wait for some time till CloudFront deletes associations from all Edge Locations.
