Expose trace sampling controls (#444)

Signed-off-by: Douglas Reid <douglas-reid@users.noreply.github.com>

envoy/api/v2/filter/network/http_connection_manager.proto

@@ -3,6 +3,7 @@ syntax = "proto3";
 package envoy.api.v2.filter.network;
 option go_package = "network";
 
+import "envoy/api/v2/base.proto";
 import "envoy/api/v2/config_source.proto";
 import "envoy/api/v2/protocol.proto";
 import "envoy/api/v2/filter/accesslog/accesslog.proto";
@@ -80,6 +81,31 @@ message HttpConnectionManager {
     // populate the tag name, and the header value is used to populate the tag value. The tag is
     // created if the specified header name is present in the request's headers.
     repeated string request_headers_for_tags = 2;
+
+    // Target percentage of requests managed by this HTTP connection manager that will be force
+    // traced if the :ref:`x-client-trace-id <config_http_conn_man_headers_x-client-trace-id>`
+    // header is set. This field is a direct analog for the runtime variable
+    // 'tracing.client_sampling' in the :ref:`HTTP Connection Manager
+    // <config_http_conn_man_runtime>`.
+    // Default: 100%
+    Percent client_sampling = 3;
+
+    // Target percentage of requests managed by this HTTP connection manager that will be randomly
+    // selected for trace generation, if not requested by the client or not forced. This field is
+    // a direct analog for the runtime variable 'tracing.random_sampling' in the
+    // :ref:`HTTP Connection Manager <config_http_conn_man_runtime>`.
+    // Default: 100%
+    Percent random_sampling = 4;
+
+    // Target percentage of requests managed by this HTTP connection manager that will be traced
+    // after all other sampling checks have been applied (client-directed, force tracing, random
+    // sampling). This field functions as an upper limit on the total configured sampling rate. For
+    // instance, setting client_sampling to 100% but overall_sampling to 1% will result in only 1%
+    // of client requests with the appropriate headers to be force traced. This field is a direct
+    // analog for the runtime variable 'tracing.global_enabled' in the
+    // :ref:`HTTP Connection Manager <config_http_conn_man_runtime>`.
+    // Default: 100%
+    Percent overall_sampling = 5;
   }
 
   // Presence of the object defines whether the connection manager