add featureflag service (Erlang/Elixir)

HTTP interface is on port FEATURE_FLAG_SERVICE_PORT and
the grpc service is run on FEATURE_FLAG_GRPC_SERVICE_PORT.

Creating and updating flags is done through the web interface.
The GRPC service only provides fetching of a flag by name.

.env

@@ -47,3 +47,6 @@ RECOMMENDATION_SERVICE_ADDR=recommendationservice:${RECOMMENDATION_SERVICE_PORT}
 
 SHIPPING_SERVICE_PORT=50051
 SHIPPING_SERVICE_ADDR=shippingservice:${SHIPPING_SERVICE_PORT}
+
+FEATURE_FLAG_SERVICE_PORT=50052
+FEATURE_FLAG_GRPC_SERVICE_PORT=50053

CHANGELOG.md

@@ -17,3 +17,5 @@ release.
   ([#26](https://github.com/open-telemetry/opentelemetry-demo-webstore/pull/26))
 * Added span attributes to frontend service
   ([#82](https://github.com/open-telemetry/opentelemetry-demo-webstore/pull/82))
+* Added feature flag service implementation
+  ([#141](https://github.com/open-telemetry/opentelemetry-demo-webstore/pull/141))

docker-compose.yml

@@ -25,6 +25,7 @@ services:
       - ./src/otelcollector/otelcol-config.yml:/etc/otelcol-config.yml
     ports:
       - "4317"
+      - "4318"
     depends_on:
       - jaeger
 
@@ -198,6 +199,29 @@ services:
       - OTEL_EXPORTER_OTLP_TRACES_ENDPOINT
       - OTEL_RESOURCE_ATTRIBUTES=service.name=shippingservice
 
+  # FeatureFlagService
+  featureflagservice:
+    build:
+      context: ./src/featureflagservice
+    ports:
+      - "${FEATURE_FLAG_SERVICE_PORT}"
+      - "${FEATURE_FLAG_GRPC_SERVICE_PORT}"
+    environment:
+      - PORT=${FEATURE_FLAG_SERVICE_PORT}
+      - GRPC_PORT=${FEATURE_FLAG_GRPC_SERVICE_PORT}
+      - OTEL_EXPORTER_OTLP_TRACES_ENDPOINT
+      - OTEL_RESOURCE_ATTRIBUTES=service.name=featureflagservice
+      - DATABASE_URL=ecto://ffs:ffs@ffs_postgres:5432/ffs
+    depends_on:
+      - ffs_postgres
+
+  ffs_postgres:
+    image: cimg/postgres:14.2
+    environment:
+      - POSTGRES_USER=ffs
+      - POSTGRES_DB=ffs
+      - POSTGRES_PASSWORD=ffs
+
   # LoadGenerator
   loadgenerator:
     image: ${IMAGE_NAME}:${IMAGE_VERSION}-loadgenerator

src/featureflagservice/.dockerignore

@@ -0,0 +1,45 @@
+# This file excludes paths from the Docker build context.
+#
+# By default, Docker's build context includes all files (and folders) in the
+# current directory. Even if a file isn't copied into the container it is still sent to
+# the Docker daemon.
+#
+# There are multiple reasons to exclude files from the build context:
+#
+# 1. Prevent nested folders from being copied into the container (ex: exclude
+#    /assets/node_modules when copying /assets)
+# 2. Reduce the size of the build context and improve build time (ex. /build, /deps, /doc)
+# 3. Avoid sending files containing sensitive information
+#
+# More information on using .dockerignore is available here:
+# https://docs.docker.com/engine/reference/builder/#dockerignore-file
+
+.dockerignore
+
+# Ignore git, but keep git HEAD and refs to access current commit hash if needed:
+#
+# $ cat .git/HEAD | awk '{print ".git/"$2}' | xargs cat
+# d0b8727759e1e0e7aa3d41707d12376e373d5ecc
+.git
+!.git/HEAD
+!.git/refs
+
+# Common development/test artifacts
+/cover/
+/doc/
+/test/
+/tmp/
+.elixir_ls
+
+# Mix artifacts
+/_build/
+/deps/
+*.ez
+
+# Generated on crash by the VM
+erl_crash.dump
+
+# Static artifacts - These should be fetched and built inside the Docker image
+/assets/node_modules/
+/priv/static/assets/
+/priv/static/cache_manifest.json

src/featureflagservice/.formatter.exs

@@ -0,0 +1,5 @@
+[
+  import_deps: [:ecto, :phoenix],
+  inputs: ["*.{ex,exs}", "priv/*/seeds.exs", "{config,lib,test}/**/*.{ex,exs}"],
+  subdirectories: ["priv/*/migrations"]
+]

src/featureflagservice/.gitignore

@@ -0,0 +1,35 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+ffs_grpc/_build/
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where 3rd-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+featureflagservice-*.tar
+
+# Ignore assets that are produced by build tools.
+/priv/static/assets/
+
+# Ignore digested assets cache.
+/priv/static/cache_manifest.json
+
+# In case you use Node.js/npm, you want to ignore these.
+npm-debug.log
+/assets/node_modules/
+
+/assets/vendor/

src/featureflagservice/Dockerfile

@@ -0,0 +1,93 @@
+# Find eligible builder and runner images on Docker Hub. We use Ubuntu/Debian instead of
+# Alpine to avoid DNS resolution issues in production.
+#
+# https://hub.docker.com/r/hexpm/elixir/tags?page=1&name=ubuntu
+# https://hub.docker.com/_/ubuntu?tab=tags
+#
+#
+# This file is based on these images:
+#
+#   - https://hub.docker.com/r/hexpm/elixir/tags - for the build image
+#   - https://hub.docker.com/_/debian?tab=tags&page=1&name=bullseye-20210902-slim - for the release image
+#   - https://pkgs.org/ - resource for finding needed packages
+#   - Ex: hexpm/elixir:1.13.3-erlang-25.0-debian-bullseye-20210902-slim
+#
+ARG ELIXIR_VERSION=1.13.3
+ARG OTP_VERSION=25.0
+ARG DEBIAN_VERSION=bullseye-20210902-slim
+
+ARG BUILDER_IMAGE="hexpm/elixir:${ELIXIR_VERSION}-erlang-${OTP_VERSION}-debian-${DEBIAN_VERSION}"
+ARG RUNNER_IMAGE="debian:${DEBIAN_VERSION}"
+
+FROM ${BUILDER_IMAGE} as builder
+
+# install build dependencies
+RUN apt-get update -y && apt-get install -y build-essential git \
+    && apt-get clean && rm -f /var/lib/apt/lists/*_*
+
+# prepare build dir
+WORKDIR /app
+
+# install hex + rebar
+RUN mix local.hex --force && \
+    mix local.rebar --force
+
+# set build ENV
+ENV MIX_ENV="prod"
+
+# install mix dependencies
+COPY mix.exs mix.lock ./
+RUN mix deps.get --only $MIX_ENV
+RUN mkdir config
+
+# copy compile-time config files before we compile dependencies
+# to ensure any relevant config change will trigger the dependencies
+# to be re-compiled.
+COPY config/config.exs config/${MIX_ENV}.exs config/
+RUN mix deps.compile
+
+COPY priv priv
+
+COPY lib lib
+
+COPY assets assets
+
+# compile assets
+RUN mix assets.deploy
+
+# Compile the release
+RUN mix compile
+
+# Changes to config/runtime.exs don't require recompiling the code
+COPY config/runtime.exs config/
+
+COPY rel rel
+RUN mix release
+
+# start a new build stage so that the final image will only contain
+# the compiled release and other runtime necessities
+FROM ${RUNNER_IMAGE}
+
+RUN apt-get update -y && apt-get install -y libstdc++6 openssl libncurses5 locales \
+  && apt-get clean && rm -f /var/lib/apt/lists/*_*
+
+# Set the locale
+RUN sed -i '/en_US.UTF-8/s/^# //g' /etc/locale.gen && locale-gen
+
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US:en
+ENV LC_ALL en_US.UTF-8
+
+WORKDIR "/app"
+RUN chown nobody /app
+
+# set runner ENV
+ENV MIX_ENV="prod"
+ENV SECRET_KEY_BASE="mNhoOKKxgyvBIwbtw0P23waQcvUOmusb2U1moG2I7JQ3Bt6+MlGb5ZTrHwqbqy7j"
+
+# Only copy the final release from the build stage
+COPY --from=builder --chown=nobody:root /app/_build/${MIX_ENV}/rel/featureflagservice ./
+
+USER nobody
+
+CMD ["/app/bin/server"]

src/featureflagservice/README.md

@@ -0,0 +1,45 @@
+# Feature Flag Service
+
+This project provides an web interface for creating and updating feature flags
+and a GRPC service for fetching the status of flags by their name. Each runs on
+their own port but are in the same Release.
+
+## Running
+
+To run individually and not part of the demo the Release can be built with
+`mix`:
+
+``` shell
+$ MIX_ENV=prod mix release
+```
+
+Then start Postgres with `docker compose`
+
+``` shell
+$ docker compose up
+```
+
+And run the Release:
+
+``` shell
+$ PHX_SERVER=1 PORT=4000 GRPC_PORT=4001 _build/prod/rel/featureflagservice/bin/featureflagservice start_iex
+```
+
+## Instrumentation
+
+Traces of interaction with the web interface is provided by the OpenTelemetry
+[Phoenix
+instrumentation](https://github.com/open-telemetry/opentelemetry-erlang-contrib/tree/main/instrumentation/opentelemetry_phoenix)
+with Spans for database queries added through the [Ecto
+instrumentation](https://github.com/open-telemetry/opentelemetry-erlang-contrib/tree/main/instrumentation/opentelemetry_ecto).
+
+The GRPC service uses [grpcbox](https://github.com/tsloughter/grpcbox) and uses
+the [grpcbox
+interceptor](https://github.com/open-telemetry/opentelemetry-erlang-contrib/tree/main/instrumentation/opentelemetry_grpcbox)
+for instrumentation.
+
+## Building Protos
+
+A copy of the `FeatureFlagService` protos from `demo.proto` are kept in
+`proto/featureflag.proto` and `rebar3 grpc gen` will update the corresponding
+Erlang module `src/ffs_featureflag_pb.erl`.

src/featureflagservice/assets/css/app.css

@@ -0,0 +1,120 @@
+/* This file is for your main application CSS */
+@import "./phoenix.css";
+
+/* Alerts and form errors used by phx.new */
+.alert {
+  padding: 15px;
+  margin-bottom: 20px;
+  border: 1px solid transparent;
+  border-radius: 4px;
+}
+.alert-info {
+  color: #31708f;
+  background-color: #d9edf7;
+  border-color: #bce8f1;
+}
+.alert-warning {
+  color: #8a6d3b;
+  background-color: #fcf8e3;
+  border-color: #faebcc;
+}
+.alert-danger {
+  color: #a94442;
+  background-color: #f2dede;
+  border-color: #ebccd1;
+}
+.alert p {
+  margin-bottom: 0;
+}
+.alert:empty {
+  display: none;
+}
+.invalid-feedback {
+  color: #a94442;
+  display: block;
+  margin: -1rem 0 2rem;
+}
+
+/* LiveView specific classes for your customization */
+.phx-no-feedback.invalid-feedback,
+.phx-no-feedback .invalid-feedback {
+  display: none;
+}
+
+.phx-click-loading {
+  opacity: 0.5;
+  transition: opacity 1s ease-out;
+}
+
+.phx-loading{
+  cursor: wait;
+}
+
+.phx-modal {
+  opacity: 1!important;
+  position: fixed;
+  z-index: 1;
+  left: 0;
+  top: 0;
+  width: 100%;
+  height: 100%;
+  overflow: auto;
+  background-color: rgba(0,0,0,0.4);
+}
+
+.phx-modal-content {
+  background-color: #fefefe;
+  margin: 15vh auto;
+  padding: 20px;
+  border: 1px solid #888;
+  width: 80%;
+}
+
+.phx-modal-close {
+  color: #aaa;
+  float: right;
+  font-size: 28px;
+  font-weight: bold;
+}
+
+.phx-modal-close:hover,
+.phx-modal-close:focus {
+  color: black;
+  text-decoration: none;
+  cursor: pointer;
+}
+
+.fade-in-scale {
+  animation: 0.2s ease-in 0s normal forwards 1 fade-in-scale-keys;
+}
+
+.fade-out-scale {
+  animation: 0.2s ease-out 0s normal forwards 1 fade-out-scale-keys;
+}
+
+.fade-in {
+  animation: 0.2s ease-out 0s normal forwards 1 fade-in-keys;
+}
+.fade-out {
+  animation: 0.2s ease-out 0s normal forwards 1 fade-out-keys;
+}
+
+@keyframes fade-in-scale-keys{
+  0% { scale: 0.95; opacity: 0; }
+  100% { scale: 1.0; opacity: 1; }
+}
+
+@keyframes fade-out-scale-keys{
+  0% { scale: 1.0; opacity: 1; }
+  100% { scale: 0.95; opacity: 0; }
+}
+
+@keyframes fade-in-keys{
+  0% { opacity: 0; }
+  100% { opacity: 1; }
+}
+
+@keyframes fade-out-keys{
+  0% { opacity: 1; }
+  100% { opacity: 0; }
+}