ilkerandClaude Opus 5
1d1a6aebb0
CI / test (push) Failing after 53s
Placement and environment generation had landed early, which made multi-node look further along than it was. A replica spanning nodes could not come up at all, and all three reasons came down to assumptions that only hold on one node. Not every rank serves HTTP. The agent health-checked every shard at its own port, but only the leader answers; workers timed out, reported Failed and took the replica with them. Engine.ServesHTTP now says which ranks serve, and a worker is judged by staying alive. That is deliberately weaker evidence: the replica's real readiness is the leader answering, which only happens once every worker has joined. A shard is not always one process. Engine.Commands returns a sequence — every command but the last is a sidecar kept alive for the shard's lifetime and torn down with it, and the last one's exit is the shard's. vLLM under Ray is why: the leader runs a Ray head and then the server against it, while a worker runs only the join and no vLLM process at all. RayCommand had been written and tested but never called, so launch_mode: ray would have run vllm serve against a cluster that did not exist. Sidecars are killed with the shard, because a Ray head left behind holds the port the next replica needs. Start order was backwards. Workers went first, on the theory that the head should wait for them. Both engines put the rendezvous point on rank 0, so a worker started first has nothing to connect to. vLLM's server blocks until the Ray cluster has the GPUs it needs, so the leader can start immediately and waits on its own. A command can now also require that rendezvous point to be listening before the next starts, bounded by a timeout so a head that never appears fails the shard instead of hanging it. Stop was also killing only the engine, leaving sidecars behind. None of this is verified against real engines — it is tested with stub processes. The Ray sequencing, and which launch mode a given vLLM version wants, can only be confirmed on hardware. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>