fix(server): return overload response for IORails admission shedding - #2334
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Greptile SummaryThe PR gives IORails non-streaming and streaming overload conditions distinct exception types and maps them to retryable OpenAI-shaped HTTP 503 responses.
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| Filename | Overview |
|---|---|
| nemoguardrails/exceptions.py | Adds distinct exception classes for non-streaming queue saturation and streaming concurrency exhaustion. |
| nemoguardrails/guardrails/iorails.py | Translates admission failures into path-specific overload exceptions while preserving rejection metrics. |
| nemoguardrails/server/api.py | Registers overload exception handlers at the shared FastAPI exception boundary. |
| nemoguardrails/server/exception_handlers.py | Produces retryable HTTP 503 envelopes with distinct overload codes and retry headers. |
| tests/server/test_error_envelope_e2e.py | Exercises both real saturation paths and verifies their HTTP status, envelope, and retry metadata. |
| tests/guardrails/test_iorails_telemetry.py | Updates request-error metric expectations to distinguish the two overload conditions. |
Flowchart
%%{init: {'theme': 'neutral'}}%%
flowchart TD
A[IORails request] --> B{Request mode}
B -->|Non-streaming| C{Admission queue full?}
C -->|Yes| D[NonStreamingWorkQueueFullError]
B -->|Streaming| E{Semaphore exhausted?}
E -->|Yes| F[StreamingCapacityExceededError]
D --> G[HTTP 503 queue_full]
F --> H[HTTP 503 streaming_capacity]
G --> I[OpenAI error envelope and Retry-After]
H --> I
Reviews (8): Last reviewed commit: "docs(iorails): name the overload excepti..." | Re-trigger Greptile
📝 WalkthroughWalkthroughThe server now maps IORails ChangesIORails queue saturation handling
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🔵 Low · up to The change improves retryable overload responses for non-streaming requests, but streaming overloads may still receive an incorrect error message from the shared handler. This is a bounded issue and the PR is mergeable with explicit owner awareness or follow-up. Suggested reviewers: 🚥 Pre-merge checks | ✅ 5 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (5 passed)
Full details: Linked Issues checkExplanation The changes satisfy issue Full details: Test Results For Major ChangesExplanation PASS. The pull request is a localized server exception-handler change: 34 added lines across two server files and one regression test. The description documents targeted test commands and results, including 43 passed tests and pre-commit checks. The changed code does not affect numerics, convergence, or performance measurements.
✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
In `@nemoguardrails/server/api.py`:
- Line 195: Update the exception handling around IORails.stream_async so
asyncio.QueueFull uses a dedicated streaming-overload exception type or handler
instead of queue_full_error_handler, while preserving the existing
admission-queue handling for non-streaming requests and returning an appropriate
streaming overload message.
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nemoguardrails/server/api.pynemoguardrails/server/exception_handlers.pytests/server/test_error_envelope_e2e.py
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Signed-off-by: Yixin Huang <yixinh@nvidia.com>
…rload Two different overload conditions both raised bare `asyncio.QueueFull`: the non-streaming admission work queue filling up (`iorails.py` submit paths) and the streaming semaphore having no free slot. The single server handler therefore told a streaming caller that the "IORails admission queue is full", which is not the queue that rejected them. The codebase already treats these as separate conditions in its metrics, via `record_stream_rejected` and `record_nonstream_rejected`. Add `StreamingCapacityExceededError` and raise it at the streaming semaphore. It subclasses `asyncio.QueueFull`, so callers already catching admission shedding are unaffected, and Starlette resolves handlers by walking the exception's MRO, so the more specific handler is selected. Both conditions still answer 503 with `retry-after`; only the message and `code` differ. Note one observable consequence: the telemetry label `error.type` is the exception class name, so a rejected stream now reports `StreamingCapacityExceededError` where it previously reported `QueueFull`. The non-streaming path is unchanged. This is inherent to using a distinct type, and it makes the two conditions separable in metrics as well as in responses. Signed-off-by: Yixin Huang <yixinh@nvidia.com>
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Please take a look at the comments. We need a separate Exception for streaming and non-streaming paths. The streaming path uses an asyncio.Semaphore and non-streaming path uses asyncio.WorkQueue.
Can you add tests which test the behaviour at the FastAPI HTTP service ? The current ones are only at the library level. The test_error_envelope_e2e.py is a good template to start from
Review feedback. `StreamingCapacityExceededError` subclassed `asyncio.QueueFull`, but the streaming path is bounded by an `asyncio.Semaphore`: nothing is queued and nothing is full, so that inheritance described the wrong mechanism. It is now a plain exception with its own handler. Add `NonStreamingWorkQueueFull` for the admission queue, which does subclass `asyncio.QueueFull` because that is what the work queue raises, and pair it with `queue_full_error_handler`. Bare `asyncio.QueueFull` stays registered so a rejection raised outside these two paths still reads as overload rather than an internal error. The non-streaming message is unchanged; only the type is more specific. Name the limit that was hit: "Streaming concurrency limit of 256 reached" rather than leaving the reader to find `STREAM_MAX_CONCURRENCY`. Replace the one-second `retry-after` with `NONSTREAMING_RETRY_AFTER_SECONDS` and `STREAMING_RETRY_AFTER_SECONDS`, both 30. A one-second hint invites a rejected client to return while the server is still shedding. The telemetry label `error.type` follows the exception class, so a rejected stream now reports `StreamingCapacityExceededError` and a rejected non-streaming request reports `NonStreamingWorkQueueFull`. Signed-off-by: Yixin Huang <yixinh@nvidia.com>
Review feedback: the existing coverage was library-level, or raised the exceptions directly at the server, which only proves the handlers are registered. Add cases that drive the real limits instead. Each puts the actual `asyncio.Semaphore` or `asyncio.Queue` into the state a saturated server reaches, then leaves the rest untouched: the limit trips inside IORails, IORails picks the exception, the server maps it, and the assertions are made on the HTTP response a client would receive. Neither path reaches a model, so no upstream is mocked. Covered: a saturated streaming semaphore returns 503 with the streaming code and retry-after; a full work queue returns 503 with the queue code and retry-after; the two are distinguishable by a client; and neither is reported as an internal error, which is the regression this PR exists for. Removing the handlers fails all four. Sharing one exception type between the paths fails the two that check a client can tell the conditions apart. Signed-off-by: Yixin Huang <yixinh@nvidia.com>
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Thanks for the review @tgasser-nv. I addressed the issues mentioned above. Here is a quick overview: Separate exceptions (fa943ed): HTTP-level tests (17d0def): added Full suite: 6271 passed, 197 skipped. |
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Looks good! Just documentation and nits to fix before merging.
PR title
- Can you change the PR name to be breaking since the streaming path now no-longer raises the
asyncio.QueueFullexception, and operational dashboards need to make the change toStreamingCapacityExceededError?
Docs
Could you update comments/docstrings/docs to reflect the new Exceptions:
QueueFull no longer exists
- docs/observability/metrics/reference.mdx:80 —
guardrails.requests.errors{error.type=QueueFull}→ {error.type=NonStreamingWorkQueueFull} (the published one; was correct at rev 1) - nemoguardrails/guardrails/iorails.py:938 —
requests.errors{error.type=QueueFull}→ {error.type=NonStreamingWorkQueueFull} - nemoguardrails/guardrails/iorails.py:1675 —
requests.errors{error.type=QueueFull}→ {error.type=StreamingCapacityExceededError} - tests/guardrails/test_iorails_telemetry.py:1169 —
requests.errors{error.type=QueueFull}→ {error.type=NonStreamingWorkQueueFull} (contradicts its own assertion 14 lines below at :1183)
Non Streaming updates
- reference.mdx:77 — "A QueueFull rejection on the non-streaming path" → NonStreamingWorkQueueFull
- iorails.py:937 — "A QueueFull rejection shows up in BOTH" → NonStreamingWorkQueueFull
- test_iorails_telemetry.py:1167 — "a QueueFull rejection is BOTH" → NonStreamingWorkQueueFull
- test_iorails_telemetry.py:1351 — "which still reports QueueFull" → NonStreamingWorkQueueFull
Streaming updates (StreamingCapacityExceededError is not a QueueFull exception)
- iorails.py:1673 — "so a QueueFull on the semaphore check bumps BOTH"
- test_iorails_telemetry.py:1322 — "rejected with asyncio.QueueFull and the stream.rejections counter increments"
- tests/guardrails/async_helpers.py:92 — "rejected with asyncio.QueueFull" (shared helper, not touched by the PR but falsified by it)
Stale examples — not false, but point readers at a label that no longer occurs
- reference.mdx:28 — "the exception class name (for example QueueFull, TimeoutError)"
- reference.mdx:156 — "For example QueueFull, TimeoutError, HTTPConnectionError, or 503"
…ngWorkQueueFullError Review nit: every other exception in `nemoguardrails/exceptions.py` ends in `Error`, so the admission-queue exception should too. Pure rename, no behavior change. It does move the non-streaming rejection's `error.type` telemetry label to `NonStreamingWorkQueueFullError`, which the following commit reflects in the metrics docs. Signed-off-by: Yixin Huang <yixinh@nvidia.com>
Review feedback: the PR split the single `asyncio.QueueFull` overload into `NonStreamingWorkQueueFullError` and `StreamingCapacityExceededError`, but the surrounding prose still said `QueueFull` — false for the streaming path, which no longer raises a `QueueFull` at all, and stale for the non-streaming one, whose `error.type` label is now the specific class. - `stream_async`'s `Raises:` now documents `StreamingCapacityExceededError`. - The IORails dual-signal comments, the metrics reference, and the `check_async` comparison table name the exception each path raises, so an operator reading them can build the right `error.type` filter. - The streaming dual-count is documented alongside the non-streaming one; it was already implemented but never written down. - Test docstrings and the `saturate_stream_semaphore` helper stop claiming a saturated semaphore raises `asyncio.QueueFull`. Comments only; no behavior change. Signed-off-by: Yixin Huang <yixinh@nvidia.com>
yixinh-nv
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Thanks @tgasser-nv — all of the above is addressed. PR title — now Rename (33bc826) — Docs (d701b23) — every line on your list, with the renamed class: Full suite: 6925 passed, 211 skipped. |
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Note on the red The workflow already knows about this: Locally, |
yixinh-nv
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Description
Map non-streaming IORails
asyncio.QueueFulladmission shedding to a retryable, OpenAI-shaped HTTP 503 response. The response carriescode: "queue_full"andRetry-After: 1, so callers can distinguish deliberate overload shedding from an internal server failure.The change is limited to the server exception boundary and includes an ASGI regression test for the status, envelope, and retry header.
Related Issue(s)
Fixes #2332
Issue assignee: @yixinh-nv
Verification
make test TEST=tests/server/test_error_envelope_e2e.py::TestIORailsAdmissionErrors WORKERS=1make test TEST=tests/server/test_error_envelope_e2e.py WORKERS=1(43 passed)uv run --locked pre-commit run --files nemoguardrails/server/api.py nemoguardrails/server/exception_handlers.py tests/server/test_error_envelope_e2e.pyNo live-provider calls or documentation changes were needed.
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Summary by CodeRabbit
queue_fullerror code.Retry-Afterheader to indicate when clients should retry.