vllm

vLLM JSON output malformed after CUDA upgrade to 12.4

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Problem Description Symptoms and Impact After upgrading the Docker image to CUDA 12.4, vLLM v0.6.3 started emitting malformed JSON for function‑calling prompts. The downstream FastAPI gateway receives a truncated or syntactically invalid JSON payload, which triggers json.JSONDecodeError exceptions and causes request drops. Log snippet from a worker thread: INFO vllm.engine.output_parser – Received partial JSON: {“name”: “search”, “parameters”: … Read more

vLLM JSON deserialization errors during high concurrency testing

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Problem: JSON Deserialization Errors in vLLM Function‑Calling under High Concurrency During sustained load testing of the /v1/chat/completions endpoint with function calling enabled, engineers observed intermittent failures such as: JSONDecodeError: Expecting value: line 1 column 1 (char 0) Tool call response schema validation failed: missing required field ‘name’ vLLM request dropped: JSON parsing error RuntimeError: Failed … Read more

vLLM inference failure after model weights update

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vLLM Inference Failure After Model Weights Update Problem Description After a scheduled model checkpoint rollout, a fleet of vLLM workers began returning errors during request handling. Typical symptoms observed across the cluster were: Log excerpt: [2024-08-07 10:12:03] ERROR vllm.engine.engine: Failed to load model: weight shape mismatch Traceback (most recent call last): File “…/vllm/engine/engine.py”, line 312, … Read more

vLLM citation formatting errors after RAG prompt augmentation

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Problem Description – Inconsistent Citation Formatting in vLLM RAG Pipelines In a production Kubernetes deployment that serves high‑throughput GPU‑accelerated inference, the vLLM engine is used to generate responses augmented with retrieved documents (RAG). The downstream reference validator expects a strict JSON payload that contains a citations array, each citation delimited by the marker syntax defined … Read more

vLLM token refresh fails after cluster restoration from snapshot

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Problem: vLLM token refresh fails after cluster restoration from snapshot During disaster‑recovery drills and production failovers, a vLLM cluster restored from a persistent snapshot repeatedly logs errors such as: TokenRefreshError: token expired Invalid token in session state Failed to refresh token: authentication failed Session token mismatch after restore Token cache not found or corrupted All … Read more

StatefulSet update fails with incompatible node configs in Kubernetes

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Problem – StatefulSet update fails with incompatible node configurations in a vLLM deployment A hybrid‑cloud environment runs a vllm StatefulSet that stores model files on Persistent Volume Claims (PVCs) and is front‑ended by an Ingress controller. After introducing a new node pool (AWS EKS) and applying a Helm upgrade that adds a nodeSelector for GPU accelerators, … Read more

vLLM model loading timeout during real-time streaming inference

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Problem: vLLM Model Loading Timeout During Real‑Time Streaming Inference In a high‑throughput, GPU‑accelerated streaming deployment, the vLLM engine aborts during start‑up with a timeout error. The failure prevents any inference requests from being served, causing a complete outage for the real‑time data pipeline. Typical error messages observed in container logs: TimeoutError: Model loading exceeded 300 … Read more

vLLM multimodal inference mismatch between image and text

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Problem Description During multimodal inference on an on‑premises server, a custom‑trained vision‑language model integrated with vLLM produces captions and answers that do not correspond to the supplied image. The generated text is either generic (e.g., “a person standing in a room”) or completely unrelated to the visual content. The failure is reproducible across different images … Read more

RAG answer extraction fails during canary deployment in vLLM

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Problem: RAG Answer Extraction Fails During Canary Deployment in vLLM During a canary rollout of a new vLLM pod (10 % of traffic) the downstream RAG post‑processor intermittently returns an empty string or raises RAGExtractorError. The symptom is observed as incomplete or incorrect answers returned to the client, while the baseline version continues to work. Typical … Read more

RAG retrieval empty results with vLLM in hybrid cloud

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Problem Description In a hybrid‑cloud deployment of a Retrieval‑Augmented Generation (RAG) pipeline that uses vLLM for inference, the retrieval step consistently returns an empty list or null despite: Valid user queries arriving at the API endpoint. Document embeddings successfully indexed in the vector store (e.g., Milvus or Pinecone). No errors reported by the vLLM server … Read more