I just reinstalled my machine and forgot to backup my ec2 .pem file... Is there any way to download this again from amazon? I can't find it anywhere.
It is my belief that for security reasons you are not allowed to do that. My guess is they probably don't keep the private key on their side either they just generate it, get the public key and save it and then allow you to download the private key.
So... bottom line is... No, you cannot download it again. Your only option is to create a new key-pair and start your instances again using this new one instead.
Hope this helps.