The Envoy xDS APIs are defined as proto3 Protocol Buffers in the api tree. They support:
Streaming delivery of xDS API updates via gRPC. This reduces resource requirements and can lower the update latency.
A new REST-JSON API in which the JSON/YAML formats are derived mechanically via the proto3 canonical JSON mapping.
Delivery of updates via the filesystem, REST-JSON or gRPC endpoints.
Advanced load balancing through an extended endpoint assignment API and load and resource utilization reporting to management servers.
Stronger consistency and ordering properties when needed. The APIs still maintain a baseline eventual consistency model.
See the xDS protocol description for further details on aspects of xDS message exchange between Envoy and the management server.