>>362 (OP)
There are many aspects to this, but the a chan is a very simple website you can write in PHP or Python. Your main concern is programmatic abuse, so you need to rate-limit users and make them pass tests that only a human can. This used to be a pain in the ass but today you have things like Cloudflare Turnstile and it's very easy. Cloudflare in general is nice because it's free and when you put it in front of your website it serves all of the images, which means your server does less work. It also allows you to block shitholes like India from posting garbage and different forms of bots. There are web crawlers, and AI scrapers and other garbage that is literally 60% of traffic on the internet. You can cut out all this shit using the AI labyrinth and other built-in tools. At very least CF obscures your server's real IP making it harder to attack.