Enhancement for adding SidecarContainers and AdditionalVolume under Spec

[DesmondH0]

Dear community,

This PR is for user able to adding any sidecar containers & additional volume to the cluster.
With this enhancement, users can easily perform tasks like exporting slow query log to ES.

Examples for both Spec Keys provided as well.
Thanks all.

[DesmondH0]

And I just signed the OCA and sent it to the email provided.

[owainlewis]

OCA approved. PR can be reviewed.

[prydie]

Hi @DesmondHoLLM, thanks for your contribution!

Whilst I think this is a useful feature I think we need to think a little on the implementation. We're adding more and more fields to allow customisation of the StatefulSet with a variable amount of consistency with existing Kubernetes API patterns.

I wonder if we would be better exposing a full PodTemplate on the Cluster CRD spec that we merge with the spec in the operator perhaps?

[DesmondH0]

Hi @prydie, thanks for the review.

About the statefulset. I think its better to be controlled by the operator with the options provided but not exposing the PodTemplate.
Which exposing the PodTemplate may lead user easily breaking the cluster and make the operator meaningless :(

[alantang888]

@prydie I worry about conflict if user can setup whole statefulset in CRD. When user make a statefulset with name mysql with some spec will conflict with operator created spec. It will have some unexpected behaviour.

So on my opinion that should only allow user modify things not direct impact to MySQL. Instead of let user can over control whole statefulset.

[DesmondH0]

Hi @prydie, may i know any update on this?

[prydie]

@DesmondHoLLM I think we need a solution that doesn't involve mounting all additional volumes under /mnt/ prior to merging (say an aditionalVolumeMounts field).

At some point I'd like to flesh out my idea of exposing a PodTemplate and merging the contents with our internal requirements, however, that needn't block this feature.