Node.js Express server: running res.render() / ejs.render() using Node.js threadpool

Question

We have an app that uses server-side rendering for SEO purposes using EJS templating.

I am well-versed with Node.js and know that it's probably possible to tap into the Node.js threadpool for asynchronous I/O for whatever purpose you want, whether it's a good idea or a bad idea. Currently I am wondering if it is possible to run ejs.render() or res.render() with a thread in the threadpool instead of the main thread in Node.js?

We are doing a lot of heavy computational lifting in the render functions and we definitely want that off the main thread, otherwise we will be paying $$$ for more servers.

Answer 1

Is it just the rendering that is concerning you? There are other template engines which should produce better results; being that template rendering should be an idempotent operation, you could additionally distribute across a cluster.

V8 will compile your code to assembly and, if your not hitting any deoptimizations or getting stalled by the garbage collector, I believe you should be in the neighborhood of your network I/O limits. I would definitely recommend you try other template engines, adding a caching HTTP reverse proxy at the front and running some benchmarks first.

Answer 2

EJS is known to be synchronous, and that's not going to change, so basically it's an inefficient rendering engine for Node.js since it blocks the JS thread whenever it renders a view, which degrades your overall throughput, especially if your rendering is CPU heavy.

You should definitely think about some other options. E.g. https://github.com/ericf/express-handlebars

If you really have CPU-heavy computation in your webserver, then Node.js is definitely not the right tool for the job anyway. There are much better servers to handle multi-threading and parallel processing. You could just setup Node to be a controller and forward your CPU-heavy requests to a backend service/server that can do the heavy-lifting.

It would be helpful to see what kind of computation you are doing during render to provide a better answer.

Tapping into the thread-pool (which is handled by libuv) would probably be a bad idea, but it is possible of course.. you just need some C++ skills and the uv_queue_work() method of the libuv library to schedule stuff on a worker thread.