[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. To that end, the Flag grpc
  message has been split into two new types, FlagEvaluationResult
  and FlagDefinition.
* Rename the UpdateFlag operation to UpdateFlagProbability, as it
  actually only updates the enabled/probability value, but not the
  description or the name.

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

@@ -266,46 +266,52 @@ message Ad {
 service FeatureFlagService {
   rpc GetFlag(GetFlagRequest) returns (GetFlagResponse) {}
   rpc CreateFlag(CreateFlagRequest) returns (CreateFlagResponse) {}
-  rpc UpdateFlag(UpdateFlagRequest) returns (UpdateFlagResponse) {}
+  rpc UpdateFlagProbability(UpdateFlagProbabilityRequest) returns (UpdateFlagProbabilityResponse) {}
   rpc ListFlags(ListFlagsRequest) returns (ListFlagsResponse) {}
   rpc DeleteFlag(DeleteFlagRequest) returns (DeleteFlagResponse) {}
 }
 
-message Flag {
+message FlagEvaluationResult {
   string name = 1;
   string description = 2;
   bool enabled = 3;
 }
 
+message FlagDefinition {
+  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;
+  FlagDefinition flag = 1;
 }
 
-message UpdateFlagRequest {
+message UpdateFlagProbabilityRequest {
   string name = 1;
-  bool enabled = 2;
+  float enabled = 2;
 }
 
-message UpdateFlagResponse {}
+message UpdateFlagProbabilityResponse {}
 
 message ListFlagsRequest {}
 
 message ListFlagsResponse {
-  repeated Flag flag = 1;
+  repeated FlagDefinition flag = 1;
 }
 
 message DeleteFlagRequest {

regenerate-grpc-code.sh

@@ -0,0 +1,92 @@
+#!/bin/sh
+
+set -euo pipefail
+
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+# This script is used to update generated code after changing demo.proto.
+
+cd -P -- "$(dirname -- "$0")"
+pwd
+
+command -v npm >/dev/null 2>&1 || {
+  cat <<EOF >&2
+npm needs to be installed but it isn't.
+
+Aborting.
+EOF
+  exit 1
+}
+
+command -v go >/dev/null 2>&1 || {
+  cat <<EOF >&2
+go needs to be installed but it isn't.
+
+Aborting.
+EOF
+  exit 1
+}
+
+command -v rebar3 >/dev/null 2>&1 || {
+  cat <<EOF >&2
+rebar3 needs to be installed but it isn't.
+
+Aborting.
+EOF
+  exit 1
+}
+
+
+command -v protoc >/dev/null 2>&1 || {
+  cat <<EOF >&2
+protoc needs to be installed but it isn't.
+
+Aborting.
+EOF
+  exit 1
+}
+
+echo "Regenerating typescript code in src/frontend based on demo.proto"
+pushd src/frontend > /dev/null
+# The npm script grpc:generate expects the pb directory to be available in the current directory (src/frontend) because it is
+# intended to be used during Docker build, where pb is copied to the same working directory as src/frontend. To get around that
+# difference, we temporarily create a symlink to pb and then remove it after the script is done.
+ln -s ../../pb pb
+npm run grpc:generate
+rm pb
+popd > /dev/null
+
+echo "Regenerating Go code in src/accountingservice based on demo.proto"
+pushd src/accountingservice > /dev/null
+go generate
+popd > /dev/null
+
+echo "Regenerating Go code in src/checkoutservice based on demo.proto"
+pushd src/checkoutservice > /dev/null
+go generate
+popd > /dev/null
+
+echo "Regenerating Go code in src/productcatalogservice based on demo.proto"
+pushd src/productcatalogservice > /dev/null
+go generate
+popd > /dev/null
+
+echo "Regenerating Java code in src/adservice based on demo.proto"
+pushd src/adservice > /dev/null
+./gradlew  generateProto
+popd > /dev/null
+
+echo "Recompiling Erlang code in src/featureflagservice based on demo.proto"
+pushd src/featureflagservice > /dev/null
+# The Erlang build expects the proto file to be available in src/featureflagservice/proto) because it is
+# intended to be used during Docker build, where demo.proto is copied to the the proto directory in the same working directory
+# as the Erlang source code. To get around that difference, we temporarily create a symlink to ../../pb as proto and then remove
+# it after the script is done.
+ln -s ../../pb proto
+rebar3 grpc_regen
+rm proto
+popd > /dev/null
+
+
+echo done

restart-service.sh

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