Specifying ssh key in ansible playbook file

The variable name you’re looking for is ansible_ssh_private_key_file.

You should set it at ‘vars’ level:

• in the inventory file:

  myHost ansible_ssh_private_key_file=~/.ssh/mykey1.pem
  myOtherHost ansible_ssh_private_key_file=~/.ssh/mykey2.pem
  

• in the host_vars:

  # host_vars/myHost.yml
  ansible_ssh_private_key_file: ~/.ssh/mykey1.pem
  
  # host_vars/myOtherHost.yml
  ansible_ssh_private_key_file: ~/.ssh/mykey2.pem
  

• in a group_vars file if you use the same key for a group of hosts

• in the vars section of an entry in a play:

  - hosts: myHost
     remote_user: ubuntu
     vars_files:
       - vars.yml
     vars:
       ansible_ssh_private_key_file: "{{ key1 }}"
     tasks:
       - name: Echo a hello message
         command: echo hello
  

• in setting a fact in a play entry (task):

  - name: 'you name it'
     ansible.builtin.set_fact:
       ansible_ssh_private_key_file: "{{ key1 }}"
  

Inventory documentation