Add proposals for client-identity rate limiting (write and query paths)#7681
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krunaljain wants to merge 4 commits into
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Add proposals for client-identity rate limiting (write and query paths)#7681krunaljain wants to merge 4 commits into
krunaljain wants to merge 4 commits into
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July 10, 2026 11:10
Cortex's ingestion and query rate limits are enforced at the tenant level only. When multiple independent services or teams share a tenant, one noisy or misbehaving client can exhaust the whole tenant's budget for everyone else, and there is no way to distinguish who, within a tenant, is responsible. Adds two companion design proposals: - client-identity-rate-limiting.md: write-path (distributor) enforcement, keyed on a new trusted X-User-ID header, following the same trust model Cortex already uses for X-Scope-OrgID. - client-identity-query-rate-limiting.md: the read-path (query-frontend) follow-on, reusing the same header and identity approach. Both are opt-in, additive to existing limits, and covered as experimental features on the proposed rollout plan. Signed-off-by: Krunal Jain <kjain25@apple.com>
Both proposals now specify global enforcement (dividing the per-client limit across healthy replicas via the existing ring/distributor-count mechanism) rather than local-only with global as a follow-up. - Write path: rename section 'Local enforcement is less precise' -> 'Global enforcement'; update enforcement description and rollout plan - Query path: rename section 'Local enforcement precision...' -> 'Global enforcement and interaction with the results cache'; update frontend/scheduler-split section, rate-limiter description, rollout plan, and open-questions cross-reference Signed-off-by: Krunal Jain <kjain25@apple.com>
The previous commit said 'global enforcement' but implied Cortex's existing divide-by-replica-count approximation. This updates both proposals to describe the intended gossip-based mechanism: - Each replica tracks a local per-client counter - Counters are gossiped to peers via the existing memberlist transport - Enforcement is against the cluster-wide sum, not a per-replica share This is more accurate than divide-by-N: it handles uneven load distribution and replica count changes without reconfiguration. The gossip convergence lag (order of memberlist gossip interval) is noted as an acceptable property of this best-effort limit. Signed-off-by: Krunal Jain <kjain25@apple.com>
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Thanks!. I have a couple of suggestions/questions
| denial-of-service vector: a caller able to set arbitrary `X-User-ID` values could grow that map | ||
| without limit simply by rotating identities. | ||
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| Cortex already solves an analogous problem elsewhere: the tenant-federation regex resolver bounds |
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The resolver in tenant federation improves latency, when the cache is full, we just follow back to being slow.
This we are talking about limiting traffic. My main question is what happens when the cache is full, do we just accept everything. I am not sure that is what we want.
Maybe there is something I am missing. can you clarify?
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When the cache is full, we intend to implement an LRU strategy to evict the earliest cache entry. This implies we might miss enforcing rate limiting for some long running users as an edge case. That said, the cache size is configurable for users.
…enforcement design - Replace 'global enforcement via gossip' with ring-based distributed enforcement: shard (tenant, client) onto the existing ring so one replica owns the authoritative counter per key; works on any ring backend (Consul/Etcd/memberlist), not memberlist-only. - Rename 'global' counter language throughout both proposals to 'distributed per-tenant' to avoid confusion with cross-tenant scope. - Move tracked_clients_limit from a process-wide cap to a per-tenant override, consistent with every other Cortex limit. - Clarify LRU eviction semantics under rate limiting: eviction resets a client's counter (allowing a brief burst), which is the intentional tradeoff over refusing new clients when the cap is full. Signed-off-by: Krunal Jain <kjain25@apple.com>
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What this PR does
Adds two companion design proposals to
docs/proposals/:client-identity-rate-limiting.md: proposes a second, optional rate-limiting dimension below the tenant on the write (ingestion) path, keyed on a new trustedX-User-IDheader, following the same trust model Cortex already uses forX-Scope-OrgID.client-identity-query-rate-limiting.md: a companion follow-on applying the same identity mechanism to query-frontend rate limiting on the read path.Motivation
Cortex enforces ingestion and query limits at the tenant level only. In practice a single tenant is often shared by multiple independent services or teams, and today's limiters cannot distinguish a well-behaved writer/querier from a noisy or misbehaving one sharing the same
X-Scope-OrgID. These proposals add an opt-in, additive mechanism to throttle by client identity below the tenant, without changing existing tenant-level behavior for anyone who doesn't configure it.Both proposals are:
Design highlights
X-User-IDheader, trusted the same way Cortex already trustsX-Scope-OrgID(i.e. no new authentication mechanism is introduced).Status
Both are filed as proposals for discussion (
Status: Proposed). No code changes are included in this PR; implementation would follow as separate PRs once the design is reviewed.Checklist