handelling 10M requests per day

We have a service that revises over 10 million requests per day. the first image is the structure of the current situation:

We have some problems now. The main part that contains PHP, Mysql is not scalable and we can not change that part at all. But we want to add a new layer before that.

In the next picture, you see a new model that contains Nodejs and Redis and MongoDB as a new layer here. Every query that has been done on MySQL also has been done on MongoDB. I mean now we have a MongoDB that has synced data by MySQL completely. We want to bring an auth layer before Mysql in MongoDB and Nodejs because this layer is scalable for us.

Nodejs will forward only valid requests to next part.

Is Nodejs a good choice here? Or it`s better to use Go Lang instead. Or Scala or Elixir or Rust? Is this model efficente in general? Will it work? What is your suggestion?