Fix active_shards_percent_as_number NaN when state not recovered

[guluo2016]

Adjusts the cluster health computation to treat indices with no routing table as unassigned.

Relates #33888
Closes #134806

[cla-checker-service]

💚 CLA has been signed

[guluo2016]

I have already signed the CLA. If I missed anything, please let me know.

Please review, thanks a lot!

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[dakrone]

I think that perhaps we should represent this as 100%, rather than 0%, since the cluster would be totally healthy if there were no shards. 0% would indicate otherwise to me.

[DaveCTurner]

I don't think we should do this. If there are indices in the metadata but no routing table then the index is totally unassigned. The only way we can get here is if we skip over those indices here:

elasticsearch/server/src/main/java/org/elasticsearch/cluster/health/ClusterStateHealth.java

Lines 89 to 91 in ffe911b

	if (indexRoutingTable == null) {
	continue;
	}

That probably made sense prior to #33888 but these days it doesn't, the only time you can get here is in a freshly-started cluster, and for that we should be saying the health is red and the assigned percentage is 0.

I think we should drop that null check and instead make the constructor of org.elasticsearch.cluster.health.ClusterIndexHealth handle a null routing table by treating it as if all the shards are unassigned.

[guluo2016]

Thanks for the review @dakrone @DaveCTurner
I’ll update the code according to the review comments.

[guluo2016]

Please review, thanks!

[DaveCTurner]

LGTM thanks for the change in approach @guluo2016

[DaveCTurner]

@elasticmachine test this please

[DaveCTurner]

This doesn't pass ./gradlew :server:test - could you take another look @guluo2016 ?

Failing tests

[guluo2016]

The update has been made.
I manually ran the test cases, and everything passed successfully.

> Task :server:test
WARNING: module-info.class ignored in patch: ...
...
BUILD SUCCESSFUL in 7m
91 actionable tasks: 2 executed, 89 up-to-date
Consider enabling configuration cache to speed up this build: https://docs.gradle.org/9.1.0/userguide/configuration_cache_enabling.html

Please take a look when you have time. Thanks! @DaveCTurner

[DaveCTurner]

@elasticmachine test this please

[DaveCTurner]

@elasticmachine test this please

[DaveCTurner]

@elasticmachine test this please

[DaveCTurner]

LGTM