Now I have written a program like the following:

// NodeJs version: v20.16.0

async function fetchFile(url: string, timeout: number): Promise<Response> {
    const controller = new AbortController()
    const id = setTimeout(() => controller.abort('timeout: ' + url), timeout)
    return fetch(url, {signal: controller.signal})
        .finally(() => clearTimeout(id))
}

const testUrl = 'https://lf3-cdn-tos.bytecdntp.com/cdn/expire-1-M/KaTeX/0.15.2/contrib/copy-tex.min.js'
const count = 100
const timeout = 5000

async function test() {
    for (let i = 0; i < count; i++) {
        try {
            await Promise.all(
                new Array(count).fill(testUrl).map(it => fetchFile(it, timeout))
            )
            console.log('success: ' + i)
        } catch (e: any) {
            console.error(`error[${i}]: ${e}`)
        }
    }
}

test()

When I run this code, frequent access timeout issues often occur, as shown in the image below.

console output

The probability of timeouts increases with the rise in concurrency, and I encountered similar issues when using node-fetch.

In this code, the same resource is being repeatedly accessed. In my actual project, I am accessing different resources concurrently, but I wrote it this way here for testing convenience. In actual testing, the resources that time out seem to be fixed; it’s always a few specific links that time out. However, when I test these links individually, they all successfully fetch within 200 milliseconds (I set the timeout to 5 seconds). The timeout issue only occurs when multiple links are fetched simultaneously.

I want to know what causes this issue and if there is a way to ensure that timeouts do not occur due to high concurrency while maximizing the level of concurrency.