[centos@ip-192-168-1-100 ~]$ ssh 192.168.1.100
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
1- By default AWS's EC2 Instance ( Virtual Machine ) use a key pair to log into it ( no password)
2- the default key pair use to log into another machine from the EC2 instance is id_rsa
3- password option is disable for SHHS Demon: ( etc/ssh/sshd_config , PasswordAuthentication yes , service sshd restart )
The easier is to use the same EC2 key pair as id_rsa:
cp EC2keypair .ssh/id_rsa
chmod 0600 .ssh/id_rsa
Other option would be to create an password for the centos user ( AWS centos EC2 instance ) + allow password in SSHD config + restart the process
then ...