nova/doc/api_samples/OS-FLV-EXT-DATA/flavors-extra-data-post-req.json

{
    "flavor": {
        "name": "flavortest",
        "ram": 1024,
        "vcpus": 2,
        "disk": 10,
        "id": "666",
        "rxtx_factor": 2.0,
        "OS-FLV-EXT-DATA:ephemeral": 30,
        "swap": 5
    }
}