docs: clarify connection duration and drain sequence behavior (#34565)

Signed-off-by: KT <39397413+ktalg@users.noreply.github.com>

Mirrored from https://github.com/envoyproxy/envoy @ 7d16b31ea529a888b0c1a5c090a117a7959766ca

envoy/config/core/v3/protocol.proto

@@ -249,10 +249,9 @@ message HttpProtocolOptions {
   google.protobuf.Duration idle_timeout = 1;
 
   // The maximum duration of a connection. The duration is defined as a period since a connection
-  // was established. If not set, there is no max duration. When max_connection_duration is reached
-  // and if there are no active streams, the connection will be closed. If the connection is a
-  // downstream connection and there are any active streams, the drain sequence will kick-in,
-  // and the connection will be force-closed after the drain period. See :ref:`drain_timeout
+  // was established. If not set, there is no max duration. When max_connection_duration is reached,
+  // the drain sequence will kick-in. The connection will be closed after the drain timeout period
+  // if there are no active streams. See :ref:`drain_timeout
   // <envoy_v3_api_field_extensions.filters.network.http_connection_manager.v3.HttpConnectionManager.drain_timeout>`.
   google.protobuf.Duration max_connection_duration = 3;
 

envoy/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto

@@ -547,9 +547,10 @@ message HttpConnectionManager {
   // race with the final GOAWAY frame. During this grace period, Envoy will
   // continue to accept new streams. After the grace period, a final GOAWAY
   // frame is sent and Envoy will start refusing new streams. Draining occurs
-  // both when a connection hits the idle timeout or during general server
-  // draining. The default grace period is 5000 milliseconds (5 seconds) if this
-  // option is not specified.
+  // either when a connection hits the idle timeout, when :ref:`max_connection_duration
+  // <envoy_v3_api_field_config.core.v3.HttpProtocolOptions.max_connection_duration>`
+  // is reached, or during general server draining. The default grace period is
+  // 5000 milliseconds (5 seconds) if this option is not specified.
   google.protobuf.Duration drain_timeout = 12;
 
   // The delayed close timeout is for downstream connections managed by the HTTP connection manager.