Specify different ssh key for each domain

1. Edit SSH config file

vi ~/.ssh/config

1. Assign different SSH key for different Domain

Host github.com
 AddKeysToAgent yes
 UseKeychain yes
 IdentityFile ~/.ssh/id_rsa

Host bitbucket.org
 AddKeysToAgent yes
 UseKeychain yes
 IdentityFile ~/.ssh/bitbucket_id_rsa