vllm: set VLLM_NIXL_SIDE_CHANNEL_HOST to node's routable IP#158
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vLLM defaults VLLM_NIXL_SIDE_CHANNEL_HOST to 0.0.0.0/localhost, which breaks the NIXL side-channel handshake across multiple nodes — workers advertise an unreachable address and KV transfer setup fails. Stamp the per-process host to the node's routable IP (same resolution already used for distributed-init leader IPs) whenever the process has a nixl_port allocated. Originally landed on the sa-submission-q2-2026 branch via NVIDIA#11 but never forward-ported to main; cherry-picking the minimal one-line behavior change here with an updated test.
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Summary
vLLM defaults
VLLM_NIXL_SIDE_CHANNEL_HOSTto0.0.0.0/localhost, which breaks the NIXL side-channel handshake when prefill and decode workers live on different nodes — the advertised host is unreachable and KV-transfer setup fails.Set the per-process host to the node's routable IP (the same resolution
build_worker_commandalready uses for the distributed-init leader) whenever a process has anixl_portallocated.Background
This fix originally landed in #11 ("Add Kimi-K2.5 vLLM recipes and fix NIXL side channel host"), but PR #11 was merged into the
sa-submission-q2-2026branch and never forward-ported tomain. Multi-node vLLM disaggregated runs againstmainstill hit the handshake failure today.Changes
src/srtctl/backends/vllm.py— whenprocess.nixl_port is not None, also stampVLLM_NIXL_SIDE_CHANNEL_HOST = get_hostname_ip(process.node)inget_process_environment().tests/test_configs.py— extendtest_vllm_get_process_environmentto assert the new env var (patchesget_hostname_ip) and add the negative assertion totest_vllm_get_process_environment_none_ports.make checkclean (718 passed, 2 skipped).Test plan
make checkpassesWORKERS_READY(no NIXL handshake errors in worker logs)