# Configurable SSH options

## Context
Projects which are using pytest-ansible are directly SSHing to the provisioned
hosts. They can be using the ansible inventory generated by Mrack as an inventory
and thus a connection information.

In testing environments where hosts changes and the tools are not expecting
actions from users, there might be some common options which users want to configure.

Such as:
- `-o 'StrictHostKeyChecking=no'` for accepting unknown hosts
- `-o 'UserKnownHostsFile=/dev/null'` for not remembering the hosts and thus
  being able to destroy them, recreate new with same hostname and still work.
- `-o 'ServerAliveInterval=60'`, `-o 'ServerAliveCountMax=5'` for more resilient
  SSH connection


Mrack is already using `StrictHostKeyChecking` and `UserKnownHostsFile` in its
ssh connection check, but they are not part of inventory and thus an SSH connection
from Ansible, if similar options are not provided by other means, will fail.

## Design

Proposal is to extend provisioning config file to be able to define additional
SSH options.

Example provisioning config snippet:

```yaml
ssh:
    options:
        StrictHostKeyChecking: 'no'
        UserKnownHostsFile: /dev/null
        ForwardX11: 'no'
        ServerAliveInterval: 60
        ServerAliveCountMax: 5
```

These values will be then used by mrack's SSH connections check and will be
added to generated Ansible inventory.

The design also allows the following future enhancements:

- possible to configure similar overrides per provider and merge them
- having it defined per-host or as global override in job metadata file
- using these values by `te` for `command` step
- extending the `ssh` dict by args (not only options)
- having common method for loading the attrs makes it usable also for other
  outputs


### Default value

If provisioning config doesn't have defined the `ssh.options` key then mrack
will use the following default values:

```yaml
StrictHostKeyChecking: 'no'
UserKnownHostsFile: /dev/null
```

This also means that having empty `ssh.options` will effectively clean the
defaults and mrack will not use any options.

### Ansible inventory output

The generated ansible inventory will be extended the the following way.

Each host dictionary will be extended with `ansible_ssh_common_args` key with
the content of the options formatted in CLI way.

E.g.:

```yaml
ansible_ssh_common_args: -o 'StrictHostKeyChecking=no' -o 'UserKnownHostsFile=/dev/null'
```

`ansible_ssh_common_args` was chosen instead of `ansible_ssh_extra_args` as
these options can be potentially useful also for `scp` and `sftp` case.

Reference:
- https://docs.ansible.com/ansible/latest/inventory_guide/intro_inventory.html#connecting-to-hosts-behavioral-inventory-parameters