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docs(routing): document sticky sessions and routing headers - #42
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Add a concept page for sticky sessions and routing keys: rid lineage keys (smg-project/smg#2206), header names (smg-project/smg#2209), rid precedence (smg-project/smg#2517), and model-scoped pins (smg-project/smg#2576). Rewrite the Manual and Routing Headers parts of both load-balancing pages and list the headers SMG reads and adds, including routing hints (smg-project/smg#2199) and x-smg-routed-worker-id (smg-project/smg#2183). Signed-off-by: Simo Lin <25425177+slin1237@users.noreply.github.com>
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WalkthroughThe documentation now describes sticky routing, routing-key precedence and validation, Manual policy assignment and failover, and applicable request and response headers. Navigation links expose the sticky-session guide and related routing concepts. ChangesSticky Routing Documentation
Priority: ⬇️ Low Estimated code review effort: 2 (Simple) | ~10 minutes Change: Other Merge Risk: 🔵 Low · up to The guide may lead operators to expect a hard per-worker concurrency cap that is not described by its own placement rules. Clarify the wording; this is a bounded documentation risk. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@src/lib/content/concepts/routing/sticky-sessions.md`:
- Line 213: Update the “Under the override” paragraph and the summary to
describe two in-flight requests as a trigger to reconsider placement, not a hard
limit: requests may still be placed on the pinned worker, so do not claim the
worker is protected from receiving more than two requests for the key.
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src/lib/config/concepts-nav.tssrc/lib/content/concepts/index.mdsrc/lib/content/concepts/routing/load-balancing.mdsrc/lib/content/concepts/routing/sticky-sessions.mdsrc/lib/content/getting-started/load-balancing.mdsrc/lib/content/reference/api/openai.md
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This was referenced Sep 24, 2026
- Describe the per-key in-flight threshold (2) as a re-placement trigger, not a hard cap: the new placement can pick the pinned worker again, so a key can exceed 2 in flight on it. - Limit promote-to-primary failover to delegate mode under the override; --policy manual always appends behind the candidate. - --eviction-interval 0 is rejected at startup under cache_aware. - manual reads X-SMG-Routing-Key without the 128-byte cap and ignores empty or non-ASCII values. - X-SMG-Target-Worker indexes the currently available workers, so indices shift; a non-numeric value also fails with 503. - A manual pin also moves after --max-idle-secs of disuse. - x-smg-routed-worker-id is set on inference responses; for a PD pair it names the decode worker. - X-SMG-Error-Code is absent from request-validation 400s. - x-api-key/x-goog-api-key apply to /v1/responses, /v1/interactions and /v1/messages; /v1/chat/completions uses only Authorization. - cache_aware matches routing-token hints in its placement index under --cache-index hash. - smg_routing_key_source_total counts every keyed request the override routes; replicas agree under consistent_hashing only when they see the same workers as available. - Use smg launch in the sticky-session and manual-policy examples. Signed-off-by: Simo Lin <25425177+slin1237@users.noreply.github.com>
Resolve the manual-policy parameter table: keep this branch's rows and the Python launcher's eviction interval default from main. Signed-off-by: Simo Lin <25425177+slin1237@users.noreply.github.com>
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Sticky routing has grown well beyond the
manualpolicy, and almost none of it was documented.--routing-key-override(alias--sticky-sessions) pins conversations on top of any policy. The key comes from the request body'sridwith turn and retry suffixes stripped (smg-project/smg#2206), with header fallbacks configurable through--routing-key-headers(#2209). A bodyridwins over a header (#2517), and pins are scoped by model (#2576). Two headers also went undocumented:x-smg-routing-tokens, a routing hint for body-free selection (#2199, #2202), andx-smg-routed-worker-idon responses (#2183). The old docs also saidmanual"requires"X-SMG-Routing-Key, which is wrong: requests without a key are served, just not pinned.Changes
concepts/routing/sticky-sessions.md:ridsuffix grammar with examples, and header validation rules.manualversus the override.delegate, failover and return, the per-key in-flight cap, and idle eviction.X-SMG-Target-Workersemantics, the priority order with the bodyrid,delegate, and the--sticky-key-idle-secsalias. No other part of those pages is touched; the routing-policies PR (docs(routing): document least_load, passthrough, and current policy behavior #40) owns them.reference/api/openai.md, Request Headers:x-request-id,x-smg-routed-worker-id,X-SMG-Error-Code,X-SMG-Preempted,Retry-After.Verification
v1.11.0(3be823a7):policies/registry.rs(key derivation, sticky map, in-flight cap)policies/manual.rs,policies/consistent_hashing.rs,policies/prefix_hash.rsrouters/common/body_policy.rscrates/external_router/src/header_utils.rs(hint limits, forward allowlist, routed-worker header)main.rsflag docs,observability/metrics.rspnpm lint,pnpm check(0 errors), andpnpm buildpass.request-streaming.md,overload-protection.md, andconfiguration.md#manual-policy-and-sticky-sessions.wrangler pages dev.This is one of a series of docs PRs that bring the site up to smg v1.11.0, one per area.
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