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Every instance can reach a metadata server at http://169.254.169.254. From inside the instance, you can read its ID and name and a topology file for the NVIDIA Collective Communications Library (NCCL). The server requires no authentication, and only the instance itself can reach it.

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Endpoints

All endpoints use GET on port 80.

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Read the instance ID and name

/v1/instance/id returns the same inst_... ID that sf instances list and the API show. /v1/instance/name returns the instance’s name, or 404 Not Found with an empty body if the instance has no name. When you rename a running instance, the endpoint returns the new name.

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Get the NCCL topology

Instances with GPUs and InfiniBand need an NCCL topology file so NCCL detects the PCIe layout correctly. /v1/nccl_xml returns this file. Save it and point NCCL_TOPO_FILE at it before you start your job.
You can also save the file to /var/run/nvidia-topologyd/virtualTopology.xml, where NCCL finds it without NCCL_TOPO_FILE. Unless the instance has both GPUs and InfiniBand, the endpoint returns 410 Gone with an empty body. NCCL detects the topology on its own there, so you do not need the file. See Multi-node training for a full InfiniBand job.