{"record":{"id":"abbc49af01d37066","repo":"vllm-project/vllm","slug":"eplb-communicator-nixl-requested-but-nixl-is-una","errorCode":null,"errorMessage":"EPLB communicator 'nixl' requested but NIXL is unavailable.","messagePattern":"EPLB communicator 'nixl' requested but NIXL is unavailable\\.","errorType":"exception","errorClass":"RuntimeError","httpStatus":null,"severity":"error","filePath":"vllm/distributed/eplb/eplb_communicator.py","lineNumber":749,"sourceCode":"        if backend == \"nixl\":\n            pass  # handled below with defer_remote_setup=True\n        elif backend not in (\"torch_nccl\", \"pynccl\"):\n            raise ValueError(\n                f\"Elastic EP requires 'torch_nccl', 'pynccl', or 'nixl' \"\n                f\"EPLB communicator (got '{backend}').\"\n            )\n        else:\n            if backend == \"torch_nccl\":\n                logger.warning(\n                    \"Stateless elastic EP requires PyNCCL backend. \"\n                    \"Forcing EPLB communicator to 'pynccl'.\"\n                )\n                backend = \"pynccl\"\n            return _create_pynccl()\n\n    if backend == \"nixl\":\n        if not has_nixl():\n            raise RuntimeError(\n                \"EPLB communicator 'nixl' requested but NIXL is unavailable.\"\n            )\n        if not (current_platform.is_cuda_alike() and tensor_device_type != \"cpu\"):\n            raise RuntimeError(\n                \"EPLB communicator 'nixl' supports only cuda-like devices \"\n                f\"(got {tensor_device_type}).\"\n            )\n        try:\n            return NixlEplbCommunicator(\n                cpu_group=group_coordinator.cpu_group,\n                all_expert_weights=expert_weights,\n                expert_buffer=expert_buffer,\n                defer_remote_setup=is_stateless,\n            )\n        except Exception as exc:\n            raise RuntimeError(\n                f\"Failed to initialize NixlEplbCommunicator ({exc}).\"\n            ) from exc","sourceCodeStart":731,"sourceCodeEnd":767,"githubUrl":"https://github.com/vllm-project/vllm/blob/c794754062d49a8fdb63ab3c5215b488b865030c/vllm/distributed/eplb/eplb_communicator.py#L731-L767","documentation":"Error \"EPLB communicator 'nixl' requested but NIXL is unavailable.\" thrown in vllm-project/vllm.","triggerScenarios":"Raised at vllm/distributed/eplb/eplb_communicator.py:749 when validation fails: EPLB communicator 'nixl' requested but NIXL is unavailable.. Typically triggered by an incompatible or incomplete vLLM configuration, an unsupported platform/backend combination, or a runtime resource/dependency that is missing.","commonSituations":"Commonly encountered at vllm/distributed/eplb/eplb_communicator.py:749 during vLLM startup/config validation or runtime setup when: (1) conflicting CLI flags or config fields are combined, (2) the current platform (CUDA/ROCm/CPU/XPU) or installed optional packages do not support the requested feature, or (3) a required value is absent or out of range. Resolve by correcting the configuration as described in the message, or by selecting a supported alternative.","solutions":["Install the NIXL package, or select a different EPLB communicator backend."],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"c794754062d49a8fdb63ab3c5215b488b865030c","analyzedAt":"2026-08-14T21:17:39.825Z","schemaVersion":2},"datasetVersion":"2026-08-15T17:31:12.345Z"}