[tools] Updating jenkins jobs through JJB can lead to unexpected results

[Igor Belikov]

Due to the way Jenkins handles updating job configuration from xml files (see https://issues.jenkins-ci.org/browse/JENKINS-21017) changes made to job yaml configuration may not be applied on Jenkins master. E.g. when 'triggers' section is completely removed from yaml configuration, it still will be in place on Jenkins master.

There is a number of ways to handle this till the issue is fixed in upstream Jenkins builds:

1. This behaviour needs to be documented in README.rst file of jenkins-jobs repo. Something like: "You need to manually apply changes to the existing job through Jenkins web-UI after completely removing one of the sections from yaml file."
2. This can be handled on jenkins-jobs level, through empty stubs for sections, using macros or some other way.
3. Upstream JJB could be patched to generate empty xml stubs for sections not mentioned in yaml config.

[Ivan (iremizov)]

Probably we could avoid such issues if we update our guidelines with such info...