{"record":{"id":"c39ae653c3fae37b","repo":"vllm-project/vllm","slug":"unknown-eplb-communicator-backend-backend","errorCode":null,"errorMessage":"Unknown EPLB communicator backend: {backend}","messagePattern":"Unknown EPLB communicator backend: (.+?)","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"vllm/distributed/eplb/eplb_communicator.py","lineNumber":776,"sourceCode":"            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\n    elif backend == \"torch_gloo\":\n        return TorchDistGlooStagedEplbCommunicator(\n            cpu_group=group_coordinator.cpu_group,\n        )\n    elif backend == \"torch_nccl\":\n        return TorchDistNcclEplbCommunicator(ep_group=torch_group)\n    elif backend == \"pynccl\":\n        return _create_pynccl()\n    raise ValueError(f\"Unknown EPLB communicator backend: {backend}\")\n","sourceCodeStart":758,"sourceCodeEnd":777,"githubUrl":"https://github.com/vllm-project/vllm/blob/c794754062d49a8fdb63ab3c5215b488b865030c/vllm/distributed/eplb/eplb_communicator.py#L758-L777","documentation":"Error \"Unknown EPLB communicator backend: {backend}\" thrown in vllm-project/vllm.","triggerScenarios":"Raised at vllm/distributed/eplb/eplb_communicator.py:776 when validation fails: Unknown EPLB communicator backend. 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:776 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":["Set a known EPLB communicator backend (e.g. 'torch_nccl', 'pynccl', or 'nixl')."],"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":"2026-08-15T22:17:37.221Z"}