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feat(sidecar): restart the vLLM sidecar when vLLM stops serving - #17728
The vLLM sidecar now exits when vLLM stops serving after startup. Its supervisor restarts it, and it registers again once vLLM is back. Today the sidecar checks vLLM's health only at startup. After a vLLM crash or shutdown the worker stays registered, and every request fails until someone restarts the sidecar.
Health watch: after start(), the sidecar keeps a gRPC health Watch on vLLM's overall health (""). Any status other than SERVING resolvesfeat(backend-common): drain and exit the worker when its engine is lost #17727's engine_lost() hook with "vLLM engine lost: ". So does the end of the stream, a stream error, or a failure to open the Watch.
Then: the worker withdraws from discovery, drains, and exits with code 1, as on SIGTERM.
In Kubernetes the operator runs the sidecar as a native sidecar container with restartPolicy: Always, so kubelet restarts only the sidecar.
The restarted sidecar waits for vLLM within --grpc-startup-deadline-secs (default 1800 s), as at any startup.
Why "": vLLM changes it only on engine failure or shutdown, never while paused or asleep.
On vLLM v0.33.0 it changes together with vllm.Inference.
Pod deletion now takes this path. Kubernetes stops the vLLM container before the native sidecar.
Effect: vLLM reports NOT_SERVING on SIGTERM, so the worker leaves discovery as soon as vLLM starts shutting down. The sidecar logs the loss at error level and exits with code 1.
With a vLLM drain: if vLLM runs with --shutdown-timeout above the sidecar's grace period (5 s), set DYN_GRACEFUL_SHUTDOWN_GRACE_PERIOD_SECS at least as high. Otherwise cleanup ends in-flight streams after the grace period.
vLLM's default --shutdown-timeout is 0, and our manifests don't set it.
Unchanged: startup (it still waits for vllm.Control and vllm.Inference), generate(), the launchers, the manifests and the gRPC transport. In-flight requests get the grace period, then cleanup releases them, as on SIGTERM today. Request migration and KV events are out of scope.
Stack: #17727 → this PR, alongside #17972 (SGLang) and #17973 (TensorRT-LLM). All three touch separate parts of the shared testkit files, so they merge in any order once #17727 lands. Design: #17643.
Where should the reviewer start?
watch_health in lib/sidecar/vllm/src/client.rs, then the end of start() and engine_lost() in lib/sidecar/vllm/src/engine.rs.
Validation
New tests
Mocker test (sidecar_mocker_integration, vLLM Mocker over real gRPC): vllm_engine_lost_on_not_serving. engine_lost() stays pending while vLLM reports SERVING. After vLLM's overall health goes NOT_SERVING, it resolves with EngineShutdown.
Process test (router_sidecar_mocker_integration, real sidecar binary): vllm_engine_loss_withdraws_worker_and_fails_the_process. The vLLM Mocker stops after the sidecar has registered. The worker must leave discovery while the process is still running. The process must then exit with code 1 and log "vLLM engine lost". A forced shutdown (exit(911)) would read as 143.
Fixture support: the vLLM Mocker fixture gains set_overall_serving().
Local runs on 963c7fa, the previous head, which watched vllm.Inference:
cargo fmt --check and cargo clippy --all-targets -D warnings are clean for backend-common and the sidecar crates.
cargo test for backend-common, the four sidecars, sidecar-common and the testkit: 666 passed, 0 failed, 9 ignored (the existing ignored live-server tests). The testkit process tests ran with --test-threads=8. With the default 24 threads on a loaded machine, some existing process tests timed out here, on earlier heads of this branch as well.
With the health watch disabled, both new tests fail. The Mocker test's engine_lost() never resolves; in the process test, the worker is never withdrawn.
GPU checks on 963c7fa (2026-11-03, 12:08–12:29 PM PST)
Setup:
One RTX 6000 Ada.
Two vllm/vllm-openai:v0.33.0 engines (sha256:d825baf9…, no patches). Each ran vllm-rs serve Qwen/Qwen3-0.6B with --enforce-eager --max-model-len 4096 --gpu-memory-utilization 0.2. Engine 1 also had --enable-sleep-mode.
One sidecar per engine, built in debug.
A Dynamo frontend (round-robin) from the CI runtime image at d7aff44. This stack doesn't change frontend code.
File-backed discovery.
Timing: times are relative to the fault on worker 1.
Case
Result
Fresh start, engine first / sidecar first
Registered 0.12 s after the sidecar started / 0.28 s after the engine was ready. 4 of 4 requests succeeded each time
docker stop of vLLM, long request in flight
Loss detected at +0.11 s ("NOT_SERVING"), instance withdrawn at +0.12 s, exit code 1 at +5.1 s. Follow-up requests: 4 of 4 succeeded, all on worker 2. The in-flight request failed. A new sidecar started while vLLM was down kept waiting, and registered 0.79 s after vLLM was ready again
docker kill of vLLM
Loss detected at +0.12 s (stream failed), withdrawn at +0.17 s, exit code 1 at +5.2 s. Follow-ups: 4 of 4 succeeded. Re-registered 0.41 s after vLLM was ready
kill -9 of only vLLM's engine-core process
vLLM reported NOT_SERVING about 2.3 s later and exited. Withdrawn at +2.47 s, exit code 1 at +7.5 s. Of 54 looping requests, the one in flight on worker 1 failed. Re-registered 0.49 s after vLLM was ready
Dynamo sleep, then wake_up
The sidecar stayed up and logged no engine loss. vLLM's vllm.Inference stayed SERVING while asleep. After wake_up, requests on worker 1 succeeded
GPU re-run on f41eed4 (the "" watch; 2026-11-03, 12:39–12:44 PM PST; same setup)
Case
Result
Fresh start, engine first
Registered 0.14 s after the engine was ready; 4 of 4 requests succeeded
docker stop of vLLM, long request in flight
Loss detected at +0.09 s ("health reported NOT_SERVING"), withdrawn at +0.10 s, exit code 1 at +5.1 s. Follow-ups: 4 of 4 succeeded on worker 2. A new sidecar started while vLLM was down waited 95 s, then registered 0.73 s after vLLM was ready
Dynamo sleep, then wake_up
"" (and vllm.Inference) stayed SERVING throughout. The sidecar stayed up, and after wake_up requests on worker 1 succeeded
Add optional availability(), recover() and on_recovered() engine hooks. The worker withdraws its endpoint while the engine is NotReady, also withdraws the model card while it is Lost, calls recover(), re-registers fresh metadata with the caller's taints, and calls on_recovered() before the endpoint is routable again. Operator pause survives recovery. Pause, resume, taint, recovery and shutdown discovery writes share one lock, record an unknown state before each write so a dropped HTTP request cannot leave a stale record, and skip endpoint writes that discovery already matches. A prefill worker whose engine is lost skips the shutdown drain.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
The vLLM sidecar watches vLLM's health stream and reports engine availability to the shared worker. It uses liveness and readiness when vLLM serves them and falls back to vllm.Inference, choosing on every connect and logging the choice. NOT_SERVING readiness (or vllm.Inference in fallback) withdraws the endpoint; NOT_SERVING liveness or any end or error of the stream is an engine loss. While lost, new requests are rejected. recover() reconnects through the same path as start(), retrying refused connections, unanswered health checks and, on a reconnect, unregistered health services until the startup deadline. on_recovered() republishes LoRA adapters once the base model card is back. vLLM channels use HTTP/2 keepalive so a silent disconnect fails within about 40 s. The vLLM launchers and manifests set --shutdown-timeout 30 so running requests drain on SIGTERM, except multinode tensor parallelism, whose headless workers exit at once.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
Per the testkit README, direct native-RPC and peer-loss behavior belongs in sidecar_mocker_integration.rs. Move the health-stream availability and reconnect tests there as explicit vLLM tests on the Mocker fixture, replacing the duplicate crash server in vllm/src/tests.rs. The testkit server can now restart on its old address, the vLLM fixture can set or clear any health service, and the KV-events switch applies to every Mocker-backed fixture.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
The vLLM client now monitors health and reports engine availability. The engine supports reconnecting after loss, and test fixtures and integration tests cover health changes, recovery, and operation without KV events. vLLM serve commands now specify a 30-second shutdown timeout.
Changes
vLLM Availability and Recovery
Layer / File(s)
Summary
Keepalive and health monitoring lib/sidecar/common/src/transport.rs, lib/sidecar/vllm/src/client.rs
The transport supports optional HTTP/2 keepalive settings. The vLLM client applies per-attempt health-check deadlines and reports availability based on health streams.
Engine availability and recovery lib/sidecar/vllm/src/engine.rs, lib/sidecar/vllm/src/tests.rs
The engine uses a replaceable client, rejects generation when availability is Lost, and reconnects through shared startup checks. Recovery reconciles loaded LoRAs.
Health and connection test support lib/sidecar/testkit/src/server.rs, lib/sidecar/testkit/tests/support/*
The test server can bind to a specified address. vLLM fixtures can set health status and restart at the same address. Fixture configuration controls KV events, and Gate can hold or reset connections.
Availability and KV-event test coverage lib/sidecar/testkit/tests/sidecar_mocker_integration.rs, lib/sidecar/testkit/tests/router_sidecar_mocker_integration.rs, lib/sidecar/testkit/README.md
Tests cover health transitions, recovery, worker withdrawal and re-registration, and requests without KV events. The README records these scenarios and the SGLang changed-role startup scenario.
vLLM Shutdown Timeout Configuration
Layer / File(s)
Summary
Set shutdown timeouts in serve commands lib/sidecar/vllm/deploy/*.yaml, lib/sidecar/vllm/launch/*.sh
vLLM serve commands in deployment manifests and launch scripts now pass --shutdown-timeout 30.
A serving vLLM engine with liveness but no readiness service can be withdrawn from discovery. Handle that health-service layout before merging.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
Check name
Status
Explanation
Resolution
Docstring Coverage
Docstring coverage is 32.14% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
Check name
Status
Explanation
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Title check
The title "feat(sidecar): restart the vLLM sidecar when vLLM stops serving" matches the main change. The PR makes the sidecar watch vLLM's gRPC health stream, withdraw the worker on NOT_SERVING, strea…
Description check
The description is detailed and covers the template's core sections in substance. Overview is a clear summary of the vLLM health watch, withdrawal, and exit-with-code-1 behavior, and the 'Where should…
Full details: Title check
Explanation
The title "feat(sidecar): restart the vLLM sidecar when vLLM stops serving" matches the main change. The PR makes the sidecar watch vLLM's gRPC health stream, withdraw the worker on NOT_SERVING, stream end, stream error, or failed Watch, and exit so the supervisor restarts it. The title names the sidecar, the vLLM trigger, and the restart behavior. The changeset also includes keepalive, LoRA republish, and test-support changes, which the title does not mention, but those are supporting changes.
Full details: Description check
Explanation
The description is detailed and covers the template's core sections in substance. Overview is a clear summary of the vLLM health watch, withdrawal, and exit-with-code-1 behavior, and the 'Where should the reviewer start' section points to specific functions. Key Changes is covered in the health watch, 'Then', 'Why', and 'Pod deletion' bullets, with 'Unchanged' listing the non-changes. Validation is extensive: new tests, local runs, and GPU checks with timings. Issues and Ongoing Work is present as 'Related Issues' with 'Part of #17643' and 'Closes DIS-3175'. The template's 'Closes #XXXX' line is phrased differently (a Jira-style ID rather than a GitHub issue link). The Pull Request Checklist (including the '/pr-checklist' skill item) is absent from the description, and the template's required structure uses '### Overview' / '### Key Changes' / '### Validation' / '### Issues and Ongoing Work' headings, whereas the author used '## Summary', '## Where should the reviewer start?', '## Validation', and '## Related Issues'. The content is substantively complete, so the check passes, with minor structural and checklist gaps noted.
Full details: Docstring Coverage
Explanation
Docstring coverage is 32.14% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 28 functions across 22 files. (4 skipped: 4 unsupported.)
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @lib/sidecar/vllm/src/client.rs:
- Around line 290-389: Update the readiness-watch handling in follow_health so a
NotFound response does not immediately mark the engine lost; fall back to
vllm.Inference when available, or use liveness as the serving signal for
liveness-only layouts. Preserve loss reporting for other watch errors and stream
failures.
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The serve loop waited on LLMEngine::recover() without watching its
endpoint, so a runtime shutdown during recovery left the worker waiting
and could re-register the model card after shutdown started. Race
recover() against the endpoint and the shutdown token; the discovery
writes before and after it still run to completion.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
A vLLM with liveness and readiness health keeps vllm.Inference
NOT_SERVING while it is paused or asleep, so a sidecar that started or
reconnected then waited for the startup deadline, and Dynamo's wake
route never opened. Wait for liveness on such a vLLM and start from its
readiness; keep waiting for vllm.Inference on vLLM without liveness.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
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Reviewed e929de3..e180795 (26 files) with three independent reviewers.
Blockers: 0. Two findings were first ranked P1 (the readiness recovery loop and the Unimplemented Watch). A three-way cross-check found both mechanisms real but kept neither as a blocker: native vllm-rs registers liveness/readiness together and its tonic-health server implements Watch. Both are listed below as P2.
10 findings: 9 × P2 and 1 × P3, mostly about health monitoring and recovery robustness in lib/sidecar/vllm.
Not checked: no reviewer built or ran anything (cargo check/clippy/fmt, unit tests, sidecar_mocker_integration, router_sidecar_mocker_integration, GPU/Kubernetes scenarios: not run). Every changed file was read.
Engine recovery now records the new model card on the admission gate
created at startup (`WorkerAdmissionGate::get`), since #17481 made
`get_or_create` fallible.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
A discovery write that failed when the engine's availability changed was
only logged, so one transient error could leave a healthy worker out of
discovery until its next change. The serve loop now retries the sync
every second until it succeeds.
Also correct the registration docs, which said these writes are never
cancelled, and the comment on skipping the drain for a lost engine.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
Its only caller is the bootstrap probe, which never reconnects; startup and recovery use wait_for_engine.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
Replace the availability, recover and on_recovered hooks with one optional
LLMEngine hook, engine_lost(). When it resolves, the Worker shuts down as on
SIGTERM (withdraw from discovery, grace period, drain, cleanup) under the
same shutdown deadline, and returns the engine's error so the process exits
and its supervisor restarts it. Engines that don't implement it never
resolve it, so their behavior is unchanged.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
Replace the in-process reconnect with #17727's engine_lost() hook. After
start(), the vLLM sidecar watches vllm.Inference health; NOT_SERVING, the end
of the stream, a stream error, or failing to open the watch resolves the hook,
so the worker withdraws, drains and exits with an error, and its supervisor
restarts it. On vLLM v0.33.0, vllm.Inference changes only on engine failure
or shutdown, so a pause or sleep does not restart the sidecar.
The previous launcher, manifest, keepalive and testkit changes are removed;
the vLLM Mocker fixture only gains a way to set vllm.Inference NOT_SERVING.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
JulienDarve
changed the title
feat(sidecar): withdraw and reconnect vLLM workers on engine loss
feat(sidecar): restart the vLLM sidecar when vLLM stops serving
Nov 3, 2026
vLLM reports its overall gRPC health ("") NOT_SERVING only on engine failure
or shutdown. On vLLM v0.33.0 it changes together with vllm.Inference, and
vLLM releases that make vllm.Inference follow readiness leave "" unchanged
while paused or asleep, so a Dynamo sleep never restarts the sidecar.
Drop the watch task's own warning, since the Worker already logs the loss,
and the disconnect half of the Mocker test, which the process test covers.
Signed-off-by: Julien Darve <jdarve@NVIDIA.com>
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Summary
The vLLM sidecar now exits when vLLM stops serving after startup. Its supervisor restarts it, and it registers again once vLLM is back. Today the sidecar checks vLLM's health only at startup. After a vLLM crash or shutdown the worker stays registered, and every request fails until someone restarts the sidecar.
start(), the sidecar keeps a gRPC health Watch on vLLM's overall health (""). Any status other than SERVING resolves feat(backend-common): drain and exit the worker when its engine is lost #17727'sengine_lost()hook with "vLLM engine lost: ". So does the end of the stream, a stream error, or a failure to open the Watch.restartPolicy: Always, so kubelet restarts only the sidecar.--grpc-startup-deadline-secs(default 1800 s), as at any startup."": vLLM changes it only on engine failure or shutdown, never while paused or asleep.vllm.Inference.vllm.Inferencefollow readiness, but they leave""alone. A sleep through Dynamo's engine-control route therefore never restarts the sidecar.--shutdown-timeoutabove the sidecar's grace period (5 s), setDYN_GRACEFUL_SHUTDOWN_GRACE_PERIOD_SECSat least as high. Otherwise cleanup ends in-flight streams after the grace period.--shutdown-timeoutis 0, and our manifests don't set it.vllm.Controlandvllm.Inference),generate(), the launchers, the manifests and the gRPC transport. In-flight requests get the grace period, then cleanup releases them, as on SIGTERM today. Request migration and KV events are out of scope.Stack: #17727 → this PR, alongside #17972 (SGLang) and #17973 (TensorRT-LLM). All three touch separate parts of the shared testkit files, so they merge in any order once #17727 lands. Design: #17643.
Where should the reviewer start?
watch_healthinlib/sidecar/vllm/src/client.rs, then the end ofstart()andengine_lost()inlib/sidecar/vllm/src/engine.rs.Validation
New tests
sidecar_mocker_integration, vLLM Mocker over real gRPC):vllm_engine_lost_on_not_serving.engine_lost()stays pending while vLLM reports SERVING. After vLLM's overall health goes NOT_SERVING, it resolves withEngineShutdown.router_sidecar_mocker_integration, real sidecar binary):vllm_engine_loss_withdraws_worker_and_fails_the_process. The vLLM Mocker stops after the sidecar has registered. The worker must leave discovery while the process is still running. The process must then exit with code 1 and log "vLLM engine lost". A forced shutdown (exit(911)) would read as 143.set_overall_serving().Local runs on 963c7fa, the previous head, which watched
vllm.Inference:cargo fmt --checkandcargo clippy --all-targets -D warningsare clean forbackend-commonand the sidecar crates.cargo testforbackend-common, the four sidecars, sidecar-common and the testkit: 666 passed, 0 failed, 9 ignored (the existing ignored live-server tests). The testkit process tests ran with--test-threads=8. With the default 24 threads on a loaded machine, some existing process tests timed out here, on earlier heads of this branch as well.engine_lost()never resolves; in the process test, the worker is never withdrawn.vllm.Inference.GPU checks on 963c7fa (2026-11-03, 12:08–12:29 PM PST)
vllm/vllm-openai:v0.33.0engines (sha256:d825baf9…, no patches). Each ranvllm-rs serve Qwen/Qwen3-0.6Bwith--enforce-eager --max-model-len 4096 --gpu-memory-utilization 0.2. Engine 1 also had--enable-sleep-mode.docker stopof vLLM, long request in flightdocker killof vLLMkill -9of only vLLM's engine-core processsleep, thenwake_upvllm.Inferencestayed SERVING while asleep. Afterwake_up, requests on worker 1 succeededGPU re-run on f41eed4 (the
""watch; 2026-11-03, 12:39–12:44 PM PST; same setup)docker stopof vLLM, long request in flightsleep, thenwake_up""(andvllm.Inference) stayed SERVING throughout. The sidecar stayed up, and afterwake_uprequests on worker 1 succeededRelated Issues
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