Rename Search Replica to Read Replica

[mch2]

Is your feature request related to a problem? Please describe

Search replica was introduced as experimental to support replicas that only provide search functionality. I propose we change this to the more commonly used read_replica naming before we GA with 3.0.

Describe the solution you'd like

Settings that would need to be updated:

index.number_of_search_only_replicas
index.auto_expand_search_replicas

Related component

Search:Performance

Describe alternatives you've considered

leave as is

Additional context

No response

[mch2]

@msfroh @andrross @prudhvigodithi @vinaykpud any concerns here?

[andrross]

@mch2 Can you call out specifically what you want to rename the settings to?

[mch2]

index.number_of_read_replicas
index.auto_expand_read_replicas

And #17803 is introducing a "strict" mode for operation routing, that one would be:

cluster.routing.read_replica.strict

[msfroh]

I like the idea. "Search only replica" is cumbersome, and "read replica" is a pretty well-understood term that aligns with what these things are.

I like the proposed setting names.

[andrross]

Looks good to me

[jainankitk]

Looks good to me as well. read replica is indeed more crisp!

[jainankitk]

Okay, I was just looking at another PR with setting - cluster.routing.search_only.strict. I am wondering if we continue to use both search_only and read_replica. Can that be confusing to the users?

[mch2]

Okay, I was just looking at another PR with setting - cluster.routing.search_only.strict. I am wondering if we continue to use both search_only and read_replica. Can that be confusing to the users?

We would rename that setting as well.

I'll go ahead and make this change, thanks for the feedback!

[vinaykpud]

In #17620 PR, we introduced Search as a Node role name. So do we need to consider renaming node role as well? Can this confuse users since now we have Search nodes hosting read replicas?