Tolerate incompatible versions with different build hash

[mosche]

Tolerate incompatible versions with different build hash.
I'm keeping the serverless feature flag to not create warnings there.

Relates to ES-11869

[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[ldematte]

I think you need to update TransportServiceHandshakeTests accordingly

[ldematte]

LGTM

[DaveCTurner]

Hang on, I don't think we can safely remove this without adding more testing of the new upgrade paths that it enables.

[mosche]

We're working on adding these tests at the moment. Though, we can definitely use the serverless flag initially for these tests and only remove the check once all tests are in place 👍

[ldematte]

++
We can hold off this change off ATM, but rest assured that we are actively working on adding these tests.

[DaveCTurner]

I see ok, yes I'd prefer we held off on merging this until we have that test coverage in place. Either that'll be quick (in which case nbd) or it'll take a while (in which case this change will cause a mess with 9.1.0 BCs)

tests are WIP elsewhere

[mark-vieira]

I see ok, yes I'd prefer we held off on merging this until we have that test coverage in place. Either that'll be quick (in which case nbd) or it'll take a while (in which case this change will cause a mess with 9.1.0 BCs)

There's a little bit of a chicken/egg though, we can't merge the testing w/o this change (as the tests would fail). But we can potentially hold off on merging this until the tests are ready and then merge both together.

[DaveCTurner]

hold off on merging this until the tests are ready and then merge both together

That would be my preference. Really I just want to avoid creating any 9.1.0 BCs without this check until there's sufficient test coverage. If we can't get the test coverage in place for 9.1.0-BC1 then maybe it'd be better to delay this until after 9.1.0 is fully released.

[ldematte]

Now that we have same-version upgrade tests on every PR and intake build, this is safe to merge.
I will let the intake/PR builds run for today, and if there are no problems I'll merge this.