upstream: adding per host connection limits (#20292)

Commit Message:
Additional Description:
Risk Level: low (off by default)
Testing: unit, integration
Docs Changes: in API
Release Notes: yes
Part of #20207

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

Mirrored from https://github.com/envoyproxy/envoy @ fc96a7683601321d3655b99d900cc8b9fd406992

envoy/config/cluster/v3/circuit_breaker.proto

@@ -105,4 +105,17 @@ message CircuitBreakers {
   // :ref:`RoutingPriority<envoy_v3_api_enum_config.core.v3.RoutingPriority>`, the default values
   // are used.
   repeated Thresholds thresholds = 1;
+
+  // Optional per-host limits which apply to each individual host in a cluster.
+  //
+  // .. note::
+  //  currently only the :ref:`max_connections
+  //  <envoy_v3_api_field_config.cluster.v3.CircuitBreakers.Thresholds.max_connections>` field is supported for per-host limits.
+  //
+  // If multiple per-host :ref:`Thresholds<envoy_v3_api_msg_config.cluster.v3.CircuitBreakers.Thresholds>`
+  // are defined with the same :ref:`RoutingPriority<envoy_v3_api_enum_config.core.v3.RoutingPriority>`,
+  // the first one in the list is used. If no per-host Thresholds are defined for a given
+  // :ref:`RoutingPriority<envoy_v3_api_enum_config.core.v3.RoutingPriority>`,
+  // the cluster will not have per-host limits.
+  repeated Thresholds per_host_thresholds = 2;
 }