Allow to override global variables per-subchart

[sheerun]

In my usecase I'd like to enable persistence for all subcharts, except redis. Ideally I'd be able to write:

title: "My Awesome App"

global:
  persistence: true # received by all subcharts

redis:
  global:
    persistence: false # override global.persistence of redis subchart
  port: 9090

what do you think? sorry if it's already possible, I cannot find documentation..

[technosophos]

I know that the Kolla Kubernetes team solved this problem with a template function. I think @kfox1111 might be able to explain.

I'm not sure if there is an existing pattern for Kubernetes Charts charts. Perhaps @prydonius knows.

[kfox1111]

Yeah, kolla-kubernetes solves this case in our shared library. Documentation is here:
https://raw.githubusercontent.com/openstack/kolla-kubernetes/master/helm/kolla-common/templates/_common_val_get.rst
The code is here:
https://github.com/openstack/kolla-kubernetes/blob/master/helm/kolla-common/templates/_common_val_get.yaml

It might be nice to merge some of is functionality into a common helm shared library of helpers? There really isn't anything kolla-kubernetes specific in the code.

[technosophos]

@kfox1111 I am trying to make it much easier to do this in Helm 2.3.0. I added a few new Sprig functions that might help:

• pluck
• first
• coalesce

I think that what you are doing above might in the future be handled by pluck "mykey" .Values .Values.globals | first. If you have a second to sanity check my thinking, here are the new docs:

https://github.com/Masterminds/sprig#lists-functions

Unit tests for pluck: https://github.com/Masterminds/sprig/blob/master/functions_test.go#L683-L696

[kfox1111]

Ah. interesting. Yeah, I think those constructs could make it much easier to implement the stuff kolla-kubernetes is doing.

If there is a canary build, it should be possible to replace the three macro's here:
https://github.com/openstack/kolla-kubernetes/blob/master/helm/kolla-common/templates/_common_val_get.yaml
with implementations that use those new functions and a ps to test in the kolla-kubernetes gate to see if it works.

Should be pretty easy I think to try.

[jascott1]

@sheerun Im closing this due to inactivity but please re-open if you need further assistance.

[tculp]

I believe this behavior would be intuitive and still have use even with the newer sprig functions. Especially with regards to boolean values, since issues like that described in Masterminds/sprig#111 still exist