Fix Ruler not starting and incorrect mkdir path when Thanos Store is enabled #16555
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The ruler will fail to start in "all" or "backend" startup target with message "Ruler storage is not configured; ruler will not be started" if Loki is configured to use the Thanos object store. The ruler configuration should be read from the 'ruler_storage' top level config key when thanos object store is enabled (-use-thanos-objstore=true or storage_config.use_thanos_objstore: true in the config file). A bug in the ruler-storage module startup check meant that the ruler.storage block that's supposed to be ignored in thanos storage mode was still being used to check whether the ruler was configured. So a placeholder ruler.storage block had to be provided to get the ruler to start, even though it would be ignored by ruler itself. Fix, so the ruler.storage block is completely ignored and can be entirely removed when thanos client is in use.
When the ruler-storage module starts, it tries to mkdir the local storage directory. This was not updated to use the path from the ruler_storage block when the thanos object store is enabled, and was still using the otherwise-ignored ruler.storage block instead. Fix so it properly uses ruler_storage.filesystem.dir or ruler_storage.local.directory when in thanos storage mode, ignoring the non-thanos-store ruler.storage.local.directory.
Emit a warning if ruler.storage is defined but ignored because
object_store.use_thanos_client: true causes the ruler_storage block
to be used instead. And vice versa when the ruler_storage config only
used with the thanos client is present, but the thanos client is not
enabled.
This is particularly important for ruler, because the thanos object
store client setting affects which ruler storage block is used even
when ruler is just using the local file system as a store.
The new warning looks like this:
level=warn msg="ruler.storage exists and is not empty, but will be ignored in favour of ruler_storage because storage_config.use_thanos_objstore is true."
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What this PR does / why we need it:
As discussed in #16543, loki does not completely switch from using the
ruler_storageconfiguration block when-use-thanos-objstore=trueorstorage_config.use_thanos_objstore: trueis set.It still uses the non-thanos-store config block
ruler.storageto:mkdirfor local rules storage during startup; andallandbackendtargetsFix both issues, so
ruler.storageis completely ignored when in thanos mode.Also add a warning when one of the config blocks is being overridden, but is non-empty, like:
and the inverse.
See also related docs change #16553
Fixes bug introduced in 8bca2e7 (#11713) per #16543 (comment)
This should be backported to v3.3.x and v3.4.x, possibly except the warning, since it's present in all releases containing the above commit.
Which issue(s) this PR fixes:
Fixes #16543
Special notes for your reviewer:
Checklist
CONTRIBUTING.mdguide (required)featPRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.docs/sources/setup/upgrade/_index.mddeprecated-config.yamlanddeleted-config.yamlfiles respectively in thetools/deprecated-config-checkerdirectory. Example PR