Node.js 中的阻塞事件循环仍然存在问题吗？

Question

I was thinking about this for a long time.

You have NGINX load balancer, which assigns web requests to particular node.js instance (you can have many of them). If one of those blocks for long time, there are web requests who are assigned to it, and are waiting inside to be run and they are stuck. This happens with round-robin load balancer. But you can choose "least-connections" option for NGINX, it means that NGINX will assign incoming web request to node.js instance, which has the lowest number of connections inside it, so web request will not go to node.js instance, where there are more of them waiting inside, it will go to one, which processes them quickly and has because of that less of them waiting inside.

So, no need to care about blocking event loop in your code.

Am I right?

Answer 1

But you can choose "least-connections" option for NGINX

Suppose Process A has a single client connected, and Process B has 100 clients.

Process A could do something to block it from accepting new connections. Nginx routes traffic to it anyway. All Nginx knows in this case is that it has 100 open connections to Process B, which is more than Process A.

The least-connections balancing option is of no practical use in this case.

So, no need to care about blocking event loop in your code.

You should at least somewhat care about this at all times. It's likely that you have things in your code that need to run periodically. If you block, they won't be able to run.

Generally , if you're actually blocking, there's probably something broken or designed poorly in your application. (Of course there is no problem with blocking if that's what you intend to do, for some particular reason. These reasons are rare.)