coredns/plugin/traffic/xds_bootstrap.json

{
        "node": {
                "id": "ENVOY_NODE_ID",
                "metadata": {
                    "TRAFFICDIRECTOR_GRPC_HOSTNAME": "trafficdirector"
            }
        },
        "xds_servers" : [{
                "server_uri": "trafficdirector.googleapis.com:443",
                "channel_creds": [
                        { "type": "google_default" }
                ]
        }]
}