Proposal for auto updating roles

Reflects discussion on ansible-devel.
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Will Thames 2016-02-19 10:38:27 +00:00
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# Auto Install Ansible roles
*Author*: Will Thames <@willthames>
*Date*: 19/02/2016
## Motivation
To use the latest (or even a specific) version of a playbook with the
appropriate roles, the following steps are typically required:
```
git pull upstream branch
ansible-galaxy install -r path/to/rolesfile.yml -p path/to/rolesdir -f
ansible-playbook run-the-playbook.yml
```
The most likely step in this process to be forgotten is the middle step. While
we can improve processes and documentation to try and ensure that this step is
not skipped, we can improve ansible-playbook so that the step is not required.
## Approaches
### Approach 1: Specify rolesfile and rolesdir in playbook
Provide new `rolesdir` and `rolesfile` keywords:
```
- hosts: application-env
become: True
rolesfile: path/to/rolesfile.yml
rolesdir: path/to/rolesdir
roles:
- roleA
- { role: roleB, tags: role_roleB }
```
Running ansible-playbook against such a playbook would cause the roles listed in
`rolesfile` to be installed in `rolesdir`.
Add new configuration to allow default rolesfile, default rolesdir and
whether or not to auto update roles (defaulting to False)
#### Advantages
- Existing mechanism for roles management is maintained
- Playbooks are not polluted with roles 'meta' information (version, source)
#### Disadvantage
- Adds two new keywords
- Adds three new configuration variables for defaults
### Approach 2: Allow rolesfile inclusion
Allow the `roles` section to include a roles file:
```
- hosts: application-env
become: True
roles:
- include: path/to/rolesfile.yml
```
Running this playbook would cause the roles to be updated from the included
roles file.
This would also be functionally equivalent to specifying the roles file
content within the playbook:
```
- hosts: application-env
become: True
roles:
- src: https://git.example.com/roleA.git
scm: git
version: 0.1
- src: https://git.example.com/roleB.git
scm: git
version: 0.3
tags: role_roleB
```
#### Advantages
- The existing rolesfile mechanism is maintained
- Uses familiar inclusion mechanism
#### Disadvantage
- Separate playbooks would need separate rolesfiles. For example, a provision
playbook and upgrade playbook would likely have some overlap - currently
you can use the same rolesfile with ansible-galaxy so that the same
roles are available but only a subset of roles is used by the smaller
playbook.
- The roles file would need to be able to include playbook features such
as role tagging.
- New configuration defaults would likely still be required (and possibly
an override keyword for rolesdir and role auto update)
## Conclusion
The author's preferred approach is currently Approach 1.
Feedback is requested to improve either approach, or provide further
approaches to solve this problem.