there were few posts related to AWS in another post related to FPGA mining and one person told that he does mine via AWS FPGA but someone also mentioned that actually amazon does not allow it and bans immediately once you get caught.
Exactly this. In the unlikely chance that you even get to use these FPGAs for crypto, AWS has automated monitoring bots that will find out you are mining. They will of course terminate your miner and your entire AWS account. I wouldn't want to go through all the hassle. If you're going to learn how to FPGA anyway just buy and invest in real machines instead.
This is false information being circulated.