Open Stack

Hi Everyone,

I'd like to discuss the usefulness of optional parameters in JJB. We've
been hit by a behaviour that is in my opinion indeterministic and causes
confusion as well as inconvenience as a user. I was reminded by this in
discussions in this patch [1] but then again this weekend while we were
trying to move to a Zuul setup.

It appears that if you update Jenkins with missing XML, it's behaviour will
be to leave the field untouched as in whatever was configured last will
remain the setting in Jenkins.

So a simple step-by-step example:

1. Create a simple job in JJB with just job name and the setting "disabled"

- job:
    name: job-name
    disabled: false

2. Look at Jenkins UI for the job. It should be in "disabled" state
3. Delete the line "disabled: false" from your YAML and update the job again
4. Look at Jenkins UI for the job. It is still in "disabled" state.
5. In the Jenkins UI enable the job
6. Update the job again with JJB and notice the Job is now still "enabled"
this time

So this means if we don't pass an XML setting to Jenkins it will always
leave the job configuration in the last state that was configured. I feel
like this result with JJB is indeterministic with this behaviour and
affects any code that does not create XML for a configuration setting if it
is not configured in YAML.

We were hit again by this issue over the weekend while trying to migrate
our jobs over to Zuul by removing the Gerrit Trigger configurations in JJB.

I feel like there shouldn't be optional settings in JJB but instead if a
user does not pass a configuration step then JJB should always set a
default for said setting so that the result is more deterministic. When I
remove a job configuration from YAML my expectation is that Jenkins will
revert the setting back to whatever the default state is rather than
Jenkins leaving the previous state.

We could potentially resolve this via work on patch [1] if there's
agreement that the behaviour on the behaviour of JJB when a setting is not
provided in YAML. My opinion is that instead of optional all parameters
should have a default setting.

Thoughts?

Thanh

[1] https://review.openstack.org/261620/
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