so I have around 10000 clients connecting to my server/website that requesting a JSON file at the same time which is around 10MB (Not getting hacked), of course, I can increase the hardware , but the problem is I can't, What can I do to solve this problem, thanks ?

Caching?

Maybe telling us something about the nature of the problem (rather than just the high bandwidth requirement) might help us think of an alternate approach.

e.g: Why do you have 10,000 clients connecting simultaneously and why do they all need a 10mb json file?

Does the file change often? Can it be compressed instead of serving raw JSON?

We'll need more information about your problem.

First: How big is the file? Is it really 10 MB? Is that compressed or uncompressed? Does your server allow pre-compressing files for gzip content-transfer-encoding?

Second: Where are you being bottlenecked here? Is it server CPU? I/O? Network throughput on host? Network throughput on ISP link?

Third: What is the mechanism that causes 10,000 users to all fetch the same file at the same time? Why can't it be cached, or pre-loaded?

Fourth: What levels of caching or content distribution networks have you already applied? How often does it change?

Fifth: Is this an actual problem you have right now, or is this a design question where you want to learn how to deal with this problem?

If you have a particular domain you can host the file on, routing it through CloudFlare Free may be enough.