overload: add a file-based injected resource monitor (#4298)

This allows injecting a synthetic resource pressure from a file, primarily intended for use in integration tests to force envoy into an overloaded state.

Testing: unit tests
Docs Changes: docs updated to reference new resource monitor

Signed-off-by: Elisha Ziskind eziskind@google.com

Mirrored from https://github.com/envoyproxy/envoy @ 12957a29bd2627bc0bba921603bd5869a449be47

docs/BUILD

@@ -58,6 +58,7 @@ proto_library(
         "//envoy/config/ratelimit/v2:rls",
         "//envoy/config/rbac/v2alpha:rbac",
         "//envoy/config/resource_monitor/fixed_heap/v2alpha:fixed_heap",
+        "//envoy/config/resource_monitor/injected_resource/v2alpha:injected_resource",
         "//envoy/config/trace/v2:trace",
         "//envoy/config/transport_socket/capture/v2alpha:capture",
         "//envoy/data/accesslog/v2:accesslog",

envoy/config/overload/v2alpha/overload.proto

@@ -21,6 +21,8 @@ message ResourceMonitor {
   //
   // * :ref:`envoy.resource_monitors.fixed_heap
   //   <envoy_api_msg_config.resource_monitor.fixed_heap.v2alpha.FixedHeapConfig>`
+  // * :ref:`envoy.resource_monitors.injected_resource
+  //   <envoy_api_msg_config.resource_monitor.injected_resource.v2alpha.InjectedResourceConfig>`
   string name = 1 [(validate.rules).string.min_bytes = 1];
 
   // Configuration for the resource monitor being instantiated.

envoy/config/resource_monitor/injected_resource/v2alpha/BUILD

@@ -0,0 +1,9 @@
+load("//bazel:api_build_system.bzl", "api_proto_library_internal")
+
+licenses(["notice"])  # Apache 2
+
+api_proto_library_internal(
+    name = "injected_resource",
+    srcs = ["injected_resource.proto"],
+    visibility = ["//visibility:public"],
+)

envoy/config/resource_monitor/injected_resource/v2alpha/injected_resource.proto

@@ -0,0 +1,16 @@
+syntax = "proto3";
+
+package envoy.config.resource_monitor.injected_resource.v2alpha;
+option go_package = "v2alpha";
+
+import "validate/validate.proto";
+
+// [#protodoc-title: Injected resource]
+
+// The injected resource monitor allows injecting a synthetic resource pressure into Envoy
+// via a text file, which must contain a floating-point number in the range [0..1] representing
+// the resource pressure and be updated atomically by a symbolic link swap.
+// This is intended primarily for integration tests to force Envoy into an overloaded state.
+message InjectedResourceConfig {
+  string filename = 1 [(validate.rules).string.min_bytes = 1];
+}