add SSH --key-file option to docs

[array-in-a-matrix]

If ssh fails when using ssh keys using the --key-file flag may solve the issue.

[spantaleev]

A better way would be to adjust your inventory with the appropriate Ansible SSH key variable pointing to the key, so you can do it once and forget about it.

Adjusting ~/.ssh/config may be another option.

Passing --ssh-key everywhere sounds like the most annoying way to solve this problem.

[spatterIight]

To throw my 2 cents in, another way is to to add a ssh_config file, relevant ssh_keys folder, and add a line to ansible.cfg

I think this is better than adjusting ~/.ssh/config since my suggested changes are localized to the repo

matrix-docker-ansible-deploy/ssh_config:

Host *
    IdentitiesOnly yes
    ServerAliveInterval 30
    UserKnownHostsFile ssh_known_hosts
    StrictHostKeyChecking accept-new

Host matrix.<matrix-domain>
     User ubuntu
     Hostname 172.28.12.5
     IdentityFile ssh_keys/matrix-key

Host *
     User root

matrix-docker-ansible-deploy/ansible.cfg

[defaults]
retry_files_enabled = False
stdout_callback = yaml

[ssh_connection]
ssh_args = -F ssh_config -o ControlMaster=auto -o ControlPersist=600s

[connection]
pipelining = True

In this way all the relevant ansible commands are the exact same, the only difference being a prompt for the key password (if there is one)