feat(llm-request-router): dynamic routing config - #2115
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📝 WalkthroughWalkthroughThe proxy accepts parameterized routing expressions, applies supported settings to configured load-balancer algorithms, and caches compiled definitions. Routing rejections produce structured HTTP 400 JSON responses. Tests and documentation cover expression parsing, cache behavior, and request handling. ChangesRouting expressions and dynamic configuration
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~60 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant Client
participant HTTPProxy
participant DynamicConfigCache
participant RoutingExpression
participant LoadBalancerRouter
Client->>HTTPProxy: Send request with routing-method header
HTTPProxy->>DynamicConfigCache: Resolve target and expression
DynamicConfigCache->>RoutingExpression: Parse and compile expression
RoutingExpression->>LoadBalancerRouter: Resolve configured algorithm
LoadBalancerRouter-->>RoutingExpression: Return resolved algorithm configuration
RoutingExpression-->>DynamicConfigCache: Return compiled definition or rejection
DynamicConfigCache-->>HTTPProxy: Return definition and cache outcome
HTTPProxy-->>Client: Return proxy response or routing error
Merge Risk: 🟡 Moderate · up to Expression routing can use more cache memory than specified and repeatedly rebuild definitions under capacity pressure or for equivalent headers. Align the cache limit, eviction policy, and expression identity with the stated requirements before merging. 🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
Full details: Linked Issues checkExplanation
Resolution Canonicalize each valid expression before cache lookup. Normalize the algorithm and equivalent parameter values, and sort parameters for identity. Share definitions by canonical configuration while counting all per-target instances against one process-wide budget. Enforce a 1,024-definition limit with LRU eviction and 15-minute idle expiry. Add tests for quoting and parameter-order identity, algorithm normalization, target-cardinality bounds, LRU eviction, updates without reload, and in-flight state isolation. Full details: Docstring CoverageExplanation Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 80 functions across 15 files. (1 skipped: 1 unsupported.) ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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Review comments at
@src/libraries/rust/stargate/crates/stargate/src/load_balancer/dynamic_config.rs:
- Around line 46-47: Add a per-process capacity of 1024 to the
`Cache::builder()` used for dynamic definitions, retaining the existing
time-to-idle and eviction-listener behavior. Add a test that inserts more than
1024 definitions and verifies definitions evicted for capacity no longer have
load-balancer instances.
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🛡️ CodeQL Analysis🚨 Found 5 issue(s) Severity Breakdown:
📋 Top Issues🔗 View full details in Security tab 🕐 Last updated: 2026-09-28 05:39:01 UTC | Commit: 51176cc |
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Inline comments:
Review comments at
@src/libraries/rust/stargate/crates/stargate/src/load_balancer/dynamic_config.rs:
- Around line 67-97: Update DynamicConfigCache::resolve to derive the cache
identity from the parsed routing expression, and use that identity for both the
existing-entry comparison and the stored DynamicConfigEntry expression instead
of the raw header. Preserve the existing definition build and outcome behavior.
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Review comments at
@src/libraries/rust/stargate/crates/stargate/src/load_balancer/dynamic_config.rs:
- Line 49: Set the cache builder’s eviction policy to LRU alongside max_capacity
so a newly built entry can displace the least recently used definition when the
cache is full. Locate the builder in the dynamic configuration cache setup and
use Moka’s EvictionPolicy::lru().
- Line 39: Set DYNAMIC_CONFIG_MAX_ENTRIES to the specified 1,024-definition
limit instead of 16,384.
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Review summary: 1 P1, 4 P2, all inline.
The parser, overlay, and cache are careful. The retire flag closes the eviction versus insert race, and the tests cover the concurrency cases well. The P1 is a trust-boundary problem: before this PR, operators alone set load-balancer tuning fields. Now function owners can set them, and cache_affinity_virtual_nodes has no upper bound, so one owner's saved expression can abort a shared router process. Please add bounds before merge. The P2s cover rebuild churn during config propagation, missing metrics, the policy fields owners can now override, and stale user docs.
| "comparator" => settings.comparator = Some(parameter.comparator()?), | ||
| "cache_affinity_virtual_nodes" => { | ||
| settings.cache_affinity_virtual_nodes = | ||
| Some(parameter.positive_unsigned()?) |
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P1: cache_affinity_virtual_nodes has no upper bound, and function owners now control it.
positive_unsigned::<usize>() accepts values up to 999999999999999. The control-plane validator (LlmRoutingMethodValidator) checks syntax only, and LoadBalancerDefinition::new accepts the value. I confirmed locally that wait-and-widen;cache_affinity_virtual_nodes=999999999999999 parses and compiles against permissive_default().
build_ring in wait_and_widen/cache_affinity.rs then runs Vec::with_capacity(candidates.len() * config.cache_affinity_virtual_nodes) on the first request that carries x-cache-affinity-key. The same expression can set cache_affinity_backend_selection_count, so the owner controls that precondition too. With two candidates the request asks for about 32 PB, and Rust aborts the process when an allocation fails. One owner's saved config can therefore abort a shared router process. Gateway retries carry the same header to the other replicas. Smaller values still cause trouble: 10,000,000 nodes with 20 backends is a multi-GB allocation, and the sort runs on a Tokio worker.
Suggest a hard cap here that rejects large values with invalid_value, plus a test. Putting the cap in WaitAndWidenConfig::from_algorithm_config would cover static config too. The other owner-settable counts look safe: n and cache_affinity_backend_selection_count are clamped to the candidate count where they are used.
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Fixed. An expression may set cache_affinity_virtual_nodes to at most 1024 (the default is 150);
Parse x-routing-method as an RFC 8941 item with parameters, overlay the parameters on the resolved load-balancer configuration, cache the effective definition per routing target, and reject invalid expressions with a 400 JSON body and error-code header. Method-only header values behave as before. Dependencies: sfv 0.15.0 with the parsed-types feature (MIT/Apache-2.0) and moka 0.12.15 with the sync feature only ((MIT OR Apache-2.0) AND Apache-2.0); both pinned with = in the stargate workspace. The lockfile also gains moka's transitive crossbeam-channel 0.5.17 and tagptr 0.2.0. The @stargate_crates Bazel hub is repinned (MODULE.bazel.lock). Relates to #536 Signed-off-by: along <along@nvidia.com>
Close the gaps between the router expression commit and the design: - Rejection messages name the offending input: an unknown method names the method, and an unknown parameter names the key and the algorithm. - A cache hit reads the entry before the per-key compute, so hits never wait behind a rebuild of the same target. - Method-only requests keep today's trimmed requested_algorithm value. - The per-target instance map stays private behind forget methods, and the idle window is one named constant. - dependencies.md lists sfv and the pinned moka version. Tests cover hit-during-rebuild, idle refresh on hits, and an expression update taking effect on the next request without a reload. Relates to #536 Signed-off-by: along <along@nvidia.com>
The dynamic-config cache now takes the definition and outcome from the compute result instead of a captured Option. The old fallback could only fire on a bug, and it would have reported that bug to the caller as a 400 invalid_value. Add a direct test of the forget-instance callback: an unknown target or definition is a no-op, and only the named definition's instance is removed. Relates to #536 Signed-off-by: along <along@nvidia.com>
Native SFV booleans (?1 and ?0) broke profile rule P4 but were reported as P2. They now get their own P4 message that points to true or false. Rename Parameter::positive to require_positive, since it checks a value rather than returning one. Relates to #536 Signed-off-by: along <along@nvidia.com>
The test that proves hits keep a cache entry alive used a 200 ms idle window with 80 ms gaps, so a stall of about 120 ms on a busy CI runner would expire the entry and fail the test. Use a 1 s window with 300 ms gaps: the hits still span longer than the window, and each gap has 700 ms of margin. Relates to #536 Signed-off-by: along <along@nvidia.com>
A test added on main builds ProxyRequestInputs without the routing_expression field this branch adds, so after the rebase the stargate test build failed. Set the field to None. Relates to #536 Signed-off-by: along <along@nvidia.com>
Limit the per-target dynamic-config cache to 16384 entries per router process as a memory backstop. The router trusts its callers, so the design bound (deployed models with an expression) holds only while the gateway is the sole caller; the cap holds regardless. The limit sits far above the expected number of deployed (function, model) pairs. moka evicts by frequency, so rare keys are dropped before busy targets. A target whose entry is not kept still routes, but its definition is rebuilt per request. The eviction listener retires and forgets evicted definitions as before, so no instances are left behind. Relates to #536 Signed-off-by: along <along@nvidia.com>
Keep the syntax, limits, error shape, and cache bounds. Drop the rule-by-rule detail; rejection messages name the rule. Relates to #1403 Signed-off-by: along <along@nvidia.com>
The cache-affinity ring allocates candidates times cache_affinity_virtual_nodes, so an unbounded owner value can exhaust memory and abort the router. Expressions may now set at most 1024 (default 150); larger values are rejected as invalid_value. Static configuration is unchanged. Relates to #1403 Signed-off-by: along <along@nvidia.com>
A quoted max_queued can reach u64::MAX, and max_engine_concurrency plus that value overflowed: a panic in debug builds and a wrapped, too-small limit in release. Saturating keeps a huge value meaning an effectively unlimited queue. Relates to #1403 Signed-off-by: along <along@nvidia.com>
Gateway replicas cache model metadata separately, so after an owner update they send the old and new expressions alternately for up to the auth cache TTL. With one slot per target every switch rebuilt the definition, reset the load-balancer state, and logged a build line. Each entry now holds its current and previous expression; either one is a hit. A third expression moves current to previous and retires only the older definition. Expiry and size eviction retire both. Relates to #1404 Signed-off-by: along <along@nvidia.com>
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TL;DR
The llm-request-router now accepts a routing expression in
x-routing-method, for examplepulsar;seed=stable-a;consider_kv_free_tokens=true. The parameters overlay the static configuration for that algorithm, and each routing target reuses one definition while its expression is unchanged. Method-only values such aspulsarroute as before.Additional Details
cache_affinity_virtual_nodesto at most 1024, since it sizes the affinity ring allocation; other ceilings are a follow-up.x-routing-methodrejection returns 400 before provider selection with the router's JSON error body andx-stargate-error-codeheader. Method-only rejections used to return a bare 400.sfv0.15.0 andmoka0.12.15 (syncfeature, the version other crates already use), both MIT or Apache-2.0. Bazel crates repinned,dependencies.mdregenerated, NOTICE unchanged.For the Reviewer
load_balancer/expression.rs(parse, overlay, rules), thenload_balancer/dynamic_config.rs(cache), thenprepare_proxy_requestinhttp_proxy.rs.forget_load_balancer_instance, called by the cache's eviction listener. A removed definition is marked retired so an in-flight request cannot re-insert its instance.For QA
cargo clippy -p stargate --all-targets -- -D warningspasses.cargo test -p stargatepasses 407 library and 149 integration tests; the bin testoccupied_metrics_port_fails_before_runtime_constructionfails the same way on main locally.Issues
Closes #1403
Closes #1404
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