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Comment by Szpadel | Hacker News Reader

The product they tried to buy what not in stock anyways, but their strategy was to constantly try anyways, so in case it would become in stock they would be the first to get it. It was all for guest checkout, so no address yet to validate nor credit card. Because they used API endpoints used by the frontend we could not use any captcha at this place because of technical requirements.

As stated before the main reason we needed to block it was volume of the traffic, you migh imagine identical scenario for dealing with DDoS attack.

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Disabling guest checkout would have been my weapon of choice or at least requiring the user to enter an email address to so that they are notified when the product becomes available.

> Because they used API endpoints used by the frontend we could not use any captcha at this place because of technical requirements

A time sensitive hash validating each request makes it a bit harder for them without significant extra work on your part. Address sensitive is much more effective but can result in issues for users that switch between networks (using your site on the move and passing between workers networks, for instance).

> Because they used API endpoints used by the frontend we could not use any captcha at this place because of technical requirements.

That doesn't compute... Captcha is almost always used in such setups.

It also looks like you could just offer an API endpoint which would return if the article is in stock or not, or even provide a webhook. Why fight them? Just make the resource usage lighter.

I'm curious now though what the articles were, if you are at liberty to share?

We had captcha, but it was at later stage of the checkout process. This API endpoint needed to work from cached pages, so it could not contain any dynamic state in request.

Some bots checked product page where we had info if product is in stock (although they tried heavenly to bypass any caches by putting garbage in URL). This kind of bots also scaled instantly to thousands checkout requests when product become available with gave no time for auto scaling to react (this was another challenge here)

This was easy to mitigate so it didn't generate almost any load on the system.

I believe we had email notification available, but it could be too high latency way for them.

I'm not sure how much I can share about articles here, but I can say that those were fairly expensive (and limited series) wardrobe products.

Hm, is probably too late, but you could have implemented in your API calls some kind of proof of work. Something that's not too onerous for a casual user but it is hard for someone trying multiple requests.

This was actually one of my ideas how to solve it, observed behaviour strongly suggested that all those thousands of IP addresses where used by single server. Even small PoW with this volume should heavly influence their capacity. But we decided that we did not want to affect performance of mobile users. We later learned that such strategy is also used by cloudflare js check

> Why fight them? Just make the resource usage lighter.

Because you presumably want real, returning customers, and that means those customers need to get a chance at buying those products, instead of them being scooped up by a scalper the millisecond they appear on the website.

Sounds like a dream having customers scooping up your products the millisecond the appear on the website. They should increase their prices.

No matter what the price, they would still have the "As stated before the main reason we needed to block it was volume of the traffic" problem that was stated above, for a popular item. In fact increasing the base price might attract even more scalpers and such.

maybe offer the item for preorder ?

I remember people doing this with PS5 when they were in short supply after release.

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