I'm not clear on why this is particularly CPU heavy, though: "the authorization service that determines whether a user is allowed to, say, publish a particular package"

Lots of users. Anything will be CPU-heavy if you give it enough work.

Except the things that end up being memory-bound instead, but the NPM database isn't large enough for that.

> Anything will be CPU-heavy if you give it enough work.

Not in a relative sense. If authorization is 5% of the work, scaling it leaves it at 5% of the work, and it's never a bottleneck. Authorization was being a significant bottleneck, not a tiny percent, and that is somewhat surprising.

Obviously authorisation will be a huge overhead compared to sendfile + nginx right? Am I misunderstanding what npm does?

I mean, to use sendfile you need to open the file, and that does a permission check too...

No I'm talking about private NPM right. The perms on the file system are not equal to (or as costly as) the auth I need to have to access my private NPM repo.

Couldn't you implement the authorization logic in, say, Redis? Then the npm service is I/O-bound again, and everyone is doing the job they're optimized for.

Authorization checks aren't that expensive. The overhead of using an external service might well make it take up more hardware overall.

It's not clear either, it makes sens to use Rust for CPU heavy task, but a CRUD service that do authentication would be fine in Nodejs since every low level crypto are using C. So I'm not sure exatly what they mean, tbh the paper is very light on details.

Some CPU heavy operations like crypto are not put in a threadpool. While it may be running C code, it will block the main thread while executing. See https://github.com/nodejs/node/issues/678

Perhaps the new worker threads may alleviate this, but I'm not sure (it's still an experimental API).

My gut feeling is that the user keys are not random generated, but actually encrypted strings that contain the permission values. Decrypting them with modern encryption algorithms (like ChaCha) is pretty CPU intensive.

"Javascript did the job", but not very well apparently. They specifically say that they "were able to forget about the Rust service because it caused so few operational issues". Add to that the increased CPU- and RAM-efficiency that generally comes with a rust implementation, and that rust rewrite looks like a no-brainer.