[ansible] how to define ssh private key for servers fetched by dynamic inventory in files

The best solution I could find for this problem is to specify private key file in ansible.cfg (I usually keep it in the same folder as a playbook):

[defaults]
inventory=ec2.py
vault_password_file = ~/.vault_pass.txt
host_key_checking = False
private_key_file = /Users/eric/.ssh/secret_key_rsa

Though, it still sets private key globally for all hosts in playbook.

Note: You have to specify full path to the key file - ~user/.ssh/some_key_rsa silently ignored.