Node http.createServer how to buffer incoming requests

I'm building a small node server that generates PDF files (using Nightmare.js). Each request calls createPage to generate one pdf.

The incoming request tend to all come around the same time, overloading the PC this is running on.

I need to buffer the incoming requests to delay execution of some requests till some of the current requests have completed. How do I do this?

function createPage(o, final) {
    //generate pdf files
}

http.createServer(function (request, response) {
    var body = [];
    request.on('data', function (chunk) { 
        body.push(chunk);
    }).on('end', function () {
        body = Buffer.concat(body).toString();
        var json = JSON.parse(body);

        createPage(json, function (status) {
            if (status === true) {
                response.writeHead(200, { 'Content-Length': 0 });
                console.log('status good');
            } else {
                response.writeHead(500, { 'Content-Type': 'text/html' });
                response.write(' ' + status);
            }
            response.end('\nEnd of Request \n');
       });
   });
}).listen(8007);

via Jeppe