Lambda function to dynamically route traffic if user-agent is crawler

seo_routing.js

// Credit: https://github.com/jinty/prerender-cloudfront
// Credit: https://aws.amazon.com/blogs/networking-and-content-delivery/dynamically-route-viewer-requests-to-any-origin-using-lambdaedge/

exports.handler = (event, context, callback) => {
    const request = event.Records[0].cf.request;
    const headers = request.headers;
    const user_agent = headers['user-agent'];
    if (user_agent) {
        var prerender = /googlebot|bingbot|yandex|baiduspider|Facebot|facebookexternalhit|twitterbot|rogerbot|linkedinbot|embedly|quora link preview|showyoubot|outbrain|pinterest|slackbot|vkShare|W3C_Validator/i.test(user_agent[0].value);
        prerender = prerender || /_escaped_fragment_/.test(request.querystring);
        prerender = prerender && ! /\.(css|xml|less|png|jpg|jpeg|gif|pdf|doc|txt|ico|rss|zip|mp3|rar|exe|wmv|doc|avi|ppt|mpg|mpeg|tif|wav|mov|psd|ai|xls|mp4|m4a|swf|dat|dmg|iso|flv|m4v|torrent|ttf|woff|svg|eot)$/i.test(request.uri);
        if (prerender) {
            // if a query string provided remove the query string and replace the ? with a + (translated to space with S3)
            if (request.querystring) {
                request.uri += `+${request.querystring}`;
                request.querystring = ''
            }

            // Return the prerendering bucket to S3
            const s3DomainName = process.env.s3DomainName;
            request.origin = {
                s3: {
                    domainName: s3DomainName,
                    region: '',
                    authMethod: 'none',
                    path: '',
                    customHeaders: {}
                }
            };
            request.headers['host'] = [{ key: 'host', value: s3DomainName }];
            console.log(user_agent[0].value, "requesting", request.uri);
        }
    }
    callback(null, request);
};