allow custom RollingUpdate configs for worker StatefulSet

[c-thiel]

What is your feature request?

Currently the Update Strategy is fixed to RollingUpdate (which is reasonable I think). What is missing is the specification of the rollingUpdate:

strategy:
  type: RollingUpdate
  # This bit is missing:
  rollingUpdate:
     maxUnavailable: 25%
     maxSurge: 1

I am running a very large Airflow Deployment with hundreds of worker pods in production. As I currently have no option to specify the rolling Update behaviour, one pod is updated at a time. This takes a very long time.

It would be great if we could add to values.yaml:

updateStrategy:
  type: RollingUpdate
  ## Optionally specify rolling update strategy
  # rollingUpdate:
  #   maxUnavailable: 25%
  #   maxSurge: 1

In the templates we could then just use a toYaml of the user specified block.

[thesuperzapper]

@c-thiel what deployment are you wanting to set the update strategy on?

For example, are you talking about the webserver?

[thesuperzapper]

@c-thiel I agree this is a good idea for workers (the other deployments arent likely to have enough Pods to worry). Plus, we are already setting specific maxSurge/maxUnavailable values for webserver/scheduler/flower Deployments.