.pem file is what you have download from AWS when you created your key-pair.
This is only a one time download and you cannot download it again.

Your software is asking for .pem file. Now you are the one who needs to locate that file. You might have downloaded it on you laptop/desktop...etc.

As I said above, .pem is not saved anywhere on EC2. It is a one time download and you have to keep it safe.

For Putty (windows ssh client), it does not support .pem format. Hence you have to convert it to .ppk format using PuTTyGen. Its essentially .pem but in a different format so that Putty can work with it.

Question #1: Whats the difference between .ppk and .pem

The .pem and .ppk files are similar because they are both private key file formats. The .pub file counterpart is the public key file format -- but that is a different story.

The differences between .pem and .ppk are the following:

System/platform compatibility .pem is kind of the de facto standard

• Linux BASH users — .pem file format
• Mac BASH users — .pem file format
• Windows/Linux/Mac PowerShell users — .pem file format
• Windows PuTTY/Cygwin users — .ppk file format

Example format of files:

.pem

-----BEGIN RSA PRIVATE KEY-----
MIIEowIBAAKCAQEAxZls7NgRS5rtDH+mCgEeqSO12BiPAY2dhZZbTkPEoDUVqG46
PHGIBBERISHFKS3xE4eMMY+uWPriviY0W12EFqYBUJDq6GmGSQPMSI8Kep7OgVGK
d2t3/Lq+I8ZqlFwAgPwS7n18mlgTV/YyA0HCCIa+kZGKqbsuylfsODUAJGQqOtUM
FKX4+O45RrJwcQGI2M+pbD4+Ow28iEsNP3flQKvamNuezm2VallhGiO/E39UITrB
27FWM1pLQo5etyE378h5q8BKMGKt1ZPxPhjiNjBefGZ1Dscw7CA5
-----END RSA PRIVATE KEY-----

.ppk

PuTTY-User-Key-File-2: ssh-rsa
Encryption: none
Comment: imported-openssh-key
Public-Lines: 3
AAAAB3NzaC1yc2EAAAADAQABAAABAQDFmWzs2BFLmu0Mf6YKAR6pI7XYGI8BjZ2F
llGIBBERISHobjo8c6DjH6iBW0UpLfETh4wxj65Y+uK+JjRbXYQWpgFQkOroaYZJ
1DxehJUvZpuZqLSUGvZrUzbYmx25oVE5+x6UBSA0NUiTpq6jWFPH
Private-Lines: 3
AAABAFLQsak2CVGhldYWLbWlsH78+3qdGFpzSuCxGoVbu63VccVMpVWutHBcVVgZ
s4GIBBERISHcVhru01cUVf8w22pOmuB0TC+qAmDZmaWTZbXslun2Dc1tGjWu4n/F
S0KOXrchN+/IeavASjBirdWT8T4Y4jYwXnxmdQ7HMOwgOQ==
Private-MAC: 5fGIBBERISHda60d2e8b049e655e4a8a78bb18dc

Question #2 : Where .pem is stored in amazons ec2 cluster?

In AWS, the .pem files are not directly stored to a single machine.

You can get the .pem file either by:

1. Starting a new instance When you create an EC2 instance, you will be given a default .pem file where you can use to access the new instance.
2. Creating a new .pem file through IAM

Credit: https://stackoverflow.com