feat(runtime-config): Add default tenant ID for runtime config fallback#7501
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feat(runtime-config): Add default tenant ID for runtime config fallback#7501
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Add -runtime-config.default-tenant-id flag that enables a synthetic tenant entry in the runtime config overrides to serve as the default for all tenants without per-tenant overrides. This allows changing default limits via the config pipeline (hot-reloaded) instead of requiring a Cortex restart. Resolution order: per-tenant override → default tenant → CLI flags. When the flag is empty (default), the feature is disabled and behavior is unchanged. This is an experimental feature. Signed-off-by: Ben Ye <benye@amazon.com>
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What this PR does
Adds a new experimental flag
-runtime-config.default-tenant-idthat enables a synthetic tenant entry in the runtime config overrides to serve as the default for all tenants without per-tenant overrides.Motivation
Today, changing default limits for all tenants (e.g.,
max_global_series_per_user) requires a Cortex restart because defaults are set via CLI flags read at startup. Per-tenant overrides, by contrast, are hot-reloaded from the runtime config file without restart.This feature allows operators to set default values in the runtime config file under a synthetic tenant ID, enabling default limit changes without pod restarts.
How it works
Resolution order when the flag is set:
When the flag is empty (default), the feature is disabled and behavior is unchanged.
Changes
pkg/util/validation/limits.go: AddeddefaultTenantIDfield toOverrides, newNewOverridesWithDefaultTenantIDconstructor, modifiedGetOverridesForUserto check default tenant before CLI flagspkg/util/runtimeconfig/manager.go: Added-runtime-config.default-tenant-idflagpkg/cortex/modules.go: Wired flag through to overrides initializationdocs/configuration/v1-guarantees.md: Listed as experimental featureExample usage
All tenants without their own override get the
__default__values. Tenants with overrides are unaffected.Checklist
make doc)