[tripleo][ansible] the current action plugins use patterns are suboptimal?

Bogdan Dobrelya bdobreli at redhat.com
Tue Aug 4 09:35:06 UTC 2020

On 8/3/20 9:28 PM, Alex Schultz wrote:
> On Mon, Aug 3, 2020 at 6:34 AM Bogdan Dobrelya <bdobreli at redhat.com> wrote:
>> On 8/3/20 12:36 PM, Sagi Shnaidman wrote:
>>> Hi, Bogdan
>>> thanks for raising this up, although I'm not sure I understand what it
>>> is the problem with using action plugins.
>>> Action plugins are well known official extensions for Ansible, as any
>>> other plugins - callback, strategy, inventory etc [1]. It is not any
>>> hack or unsupported workaround, it's a known and official feature of
>>> Ansible. Why can't we use it? What makes it different from filter,
>> I believe the cases that require the use of those should be justified.
>> For the given example, that manages containers in a loop via calling a
>> module, what the written custom callback plugin buys for us? That brings
>> code to maintain, extra complexity, like handling possible corner cases
>> in async mode, dry-run mode etc. But what is justification aside of
>> looks handy?
> I disagree that we shouldn't use action plugins or modules.  Tasks
> themselves are expensive at scale.  We saw that when we switched away
> from paunch to container management in pure ansible tasks.  This
> exposed that looping tasks are even more expensive and complex error
> handling and workflows are better suited for modules or action plugins
> than a series of tasks.  This is not something to be "fixed in
> ansible".  This is the nature of the executor and strategy related
> interactions.  Should everything be converted to modules and plugins?
> no.  Should everything be tasks only? no.  It's a balance that must be
> struck between when a specific set of complex tasks need extra data
> processing or error handling.  Switching to modules or action plugins
> allows us to unit test our logic. Using tasks do not have such a

I can understand that ansible should not be fixed for some composition 
tasks what require iterations and have complex logic for its "unit of 
work". And such ones also should be unit tested indeed. What I do not 
fully understand though is then what abandoning paunch for its action 
plugin had bought for us in the end?

Paunch was self-contained and had no external dependencies on 
fast-changing ansible frameworks. There was also no need for paunch to 
handle the ansible-specific execution strategies and nuances, like "what 
if that action plugin is called in async or in the check-mode?" Unit 
tests exited in paunch as well. It was easy to backport changes within a 
single code base.

So, looking back retrospectively, was rewriting paunch as an action 
plugin a simplification of the deployment framework? Please reply to 
yourself honestly. It does pretty same things but differently and added 
external framework. It is now also self-contained action plugin, since 
traditional tasks cannot be used in loops for this goal because of 
performance reasons.

To summarize, action plugins may be a good solution indeed, but perhaps 
we should go back and use paunch instead of ansible? Same applies for 
*some* other tasks? That would also provide a balance, for action 
plugins, tasks and common sense.

> concept outside of writing complex molecule testing.   IMHO it's safer
> to switch to modules/action plugins than writing task logic.
> IMHO the issue that I see with the switch to Action plugins is the
> increased load on the ansible "controller" node during execution.
> Modules may be better depending on the task being managed. But I
> believe with unit testing, action plugins or modules provide a cleaner
> and more testable solution than writing roles consisting only of
> tasks.
>>> lookup, inventory or any other plugin we already use?
>>> Action plugins are also used wide in Ansible itself, for example
>>> templates plugin is implemented with action plugin [2]. If Ansible can
>>> use it, why can't we? I don't think there is something with "fixing"
>>> Ansible, it's not a bug, this is a useful extension.
>>> What regards the mentioned action plugin for podman containers, it
>>> allows to spawn containers remotely while skipping the connection part
>>> for every cycle. I'm not sure you can "fix" Ansible not to do that, it's
>>> not a bug. We may not see the difference in a few hosts in CI, but it
>>> might be very efficient when we deploy on 100+ hosts oro even 1000+
>>> hosts. In order to evaluate this on bigger setups to understand its
>>> value we configured both options - to use action plugin or usual module.
>>> If better performance of action plugin will be proven, we can switch to
>>> use it, if it doesn't make a difference on bigger setups - then I think
>>> we can easily switch back to using an usual module.
>>> Thanks
>>> [1] https://docs.ansible.com/ansible/latest/plugins/plugins.html
>>> [2]
>>> https://github.com/ansible/ansible/blob/devel/lib/ansible/plugins/action/template.py
>>> On Mon, Aug 3, 2020 at 11:19 AM Bogdan Dobrelya <bdobreli at redhat.com
>>> <mailto:bdobreli at redhat.com>> wrote:
>>>      There is a trend of writing action plugins, see [0], for simple things,
>>>      like just calling a module in a loop. I'm not sure that is the
>>>      direction
>>>      TripleO should go. If ansible is inefficient in this sort of tasks
>>>      without custom python code written, we should fix ansible. Otherwise,
>>>      what is the ultimate goal of that trend? Is that having only action
>>>      plugins in roles and playbooks?
>>>      Please kindly asking the community to stop that, make a step back and
>>>      reiterate with the taken approach. Thank you.
>>>      [0] https://review.opendev.org/716108
>>>      --
>>>      Best regards,
>>>      Bogdan Dobrelya,
>>>      Irc #bogdando
>>> --
>>> Best regards
>>> Sagi Shnaidman
>> --
>> Best regards,
>> Bogdan Dobrelya,
>> Irc #bogdando

Best regards,
Bogdan Dobrelya,
Irc #bogdando

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