[featureflag] expose feature flag API via frontend

Also, propagate the change from bool to float introduced in
open-telemetry#1237
more consistently via proto definitions by differentiating between
the GetFlag operation (which evaluates the probabilty and therefore
returns a bool) and all other operations, which need to operate with
a float value/probability directly.

docker-compose.yml

@@ -286,6 +286,7 @@ services:
       - CART_SERVICE_ADDR
       - CHECKOUT_SERVICE_ADDR
       - CURRENCY_SERVICE_ADDR
+      - FEATURE_FLAG_GRPC_SERVICE_ADDR
       - PRODUCT_CATALOG_SERVICE_ADDR
       - RECOMMENDATION_SERVICE_ADDR
       - SHIPPING_SERVICE_ADDR

pb/demo.proto

@@ -271,41 +271,47 @@ service FeatureFlagService {
   rpc DeleteFlag(DeleteFlagRequest) returns (DeleteFlagResponse) {}
 }
 
-message Flag {
+message FlagEvaluationResult {
   string name = 1;
   string description = 2;
   bool enabled = 3;
 }
 
+message FlagProbability {
+  string name = 1;
+  string description = 2;
+  float enabled = 3;
+}
+
 message GetFlagRequest {
   string name = 1;
 }
 
 message GetFlagResponse {
-  Flag flag = 1;
+  FlagEvaluationResult flag = 1;
 }
 
 message CreateFlagRequest {
   string name = 1;
   string description = 2;
-  bool enabled = 3;
+  float enabled = 3;
 }
 
 message CreateFlagResponse {
-  Flag flag = 1;
+  FlagProbability flag = 1;
 }
 
 message UpdateFlagRequest {
   string name = 1;
-  bool enabled = 2;
+  float enabled = 2;
 }
 
 message UpdateFlagResponse {}
 
 message ListFlagsRequest {}
 
 message ListFlagsResponse {
-  repeated Flag flag = 1;
+  repeated FlagProbability flag = 1;
 }
 
 message DeleteFlagRequest {

restart-service.sh

@@ -1,4 +1,7 @@
 #!/bin/sh
+
+set -euo pipefail
+
 # Copyright The OpenTelemetry Authors
 # SPDX-License-Identifier: Apache-2.0