Support setting etcd server configuration as a generic key-value map in the `Etcd` spec

[shreyas-s-rao]

How to categorize this issue?

/area usability
/kind enhancement api-change

What would you like to be added:

Support setting etcd fserver configuration fields/flags as a generic key-value map in the Etcd spec.

Why is this needed:

Currently, the Etcd spec exposes specific fields from the etcd configuration that we (druid maintainers) feel are necessary. While this is sufficient for now, time and again we see the need to support additional etcd config fields in the Etcd spec, so that users can configure their etcd cluster as they wish. In such a context, adding a field to the API every time is cumbersome and a waste of time and effort.

I would propose that we provide a key-value map in a new spec.etcd.config section, so that users can set any config flags they want, and this can be directly translated into the configmap that druid creates for the etcd server.

Of course, we should have etcd-version based validation of the config, so that users are prevented from setting invalid config fields/values. This validation can be done wither by druid (in which case druid needs to know etcd-specific config semantics), or can be done by etcd-wrapper, since that is the best actor to know the etcd version and its specific valid configuration.

Note:

This is just a proposal at this time. Please feel free to discuss/debate it on this issue thread.