You can use the management console to create a key pair. ECS stores the public key and you store the private key.
in the upper left corner and select your region and project.The default key pair name consists of KeyPair- and four random characters in the "KeyPair-xxxx" format. Change it to an easy-to-remember one, for example, KeyPair-xxxx_ecs.
This is the only chance for you to save the private key file. Keep it secure. You'll need to provide the key pair name when you create an ECS, and the corresponding private key each time you connect to the ECS through SSH.