vLLM's mp launch gave workers no rank and the leader's address as their
own VLLM_HOST_IP; every node now runs serve with --nnodes, --node-rank,
--master-addr and --master-port, and the workers --headless, as vLLM
documents it.
NCCL_SOCKET_IFNAME and GLOO_SOCKET_IFNAME were the control plane's one
interface name for every node; the agent already worked out its own -
the one holding its management address - and now uses it.
On RoCE, NCCL's default GID index is a v1 link-local entry on most hosts,
which does not route. The agent finds the RoCE v2 entry holding an IPv4
address and passes it as NCCL_IB_GID_INDEX; InfiniBand gets none.
A worker whose only process needs the leader - a Ray join - started
without waiting for it, since the wait was honoured for sidecars alone;
it found no head, exited and failed the replica. It now waits.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
