xds: apply node identifier optimization (#7876)

Omit the node identifier from subsequent discovery requests on the same stream.
Restricted to non-incremental xDS for tractability.

Risk Level: low, affects xDS protocol but guarded by an option
Testing: Unit/integration tests are updated
Docs Changes: xDS spec clarification
Release Notes: omit the node identifier from subsequent discovery requests

Fixes: #7860

Signed-off-by: Kuat Yessenov <kuat@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 8e07e8297d7d5e68cf6d6d7e49ba98d2500cdef7

envoy/api/v2/core/config_source.proto

@@ -65,6 +65,9 @@ message ApiConfigSource {
   // For GRPC APIs, the rate limit settings. If present, discovery requests made by Envoy will be
   // rate limited.
   RateLimitSettings rate_limit_settings = 6;
+
+  // Skip the node identifier in subsequent discovery requests for streaming gRPC config types.
+  bool set_node_on_first_message_only = 7;
 }
 
 // Aggregated Discovery Service (ADS) options. This is currently empty, but when

xds_protocol.rst

@@ -135,6 +135,13 @@ versioning across resource types. When ADS is not used, even each
 resource of a given resource type may have a distinct version, since the
 Envoy API allows distinct EDS/RDS resources to point at different :ref:`ConfigSources <envoy_api_msg_core.ConfigSource>`.
 
+Only the first request on a stream is guaranteed to carry the node identifier.
+The subsequent discovery requests on the same stream may carry an empty node
+identifier. This holds true regardless of the acceptance of the discovery
+responses on the same stream. The node identifier should always be identical if
+present more than once on the stream. It is sufficient to only check the first
+message for the node identifier as a result.
+
 .. _xds_protocol_resource_update:
 
 Resource Update