sync-service: only include telemetry dependencies and processes in application target build (#2379)

configure telemetry dependencies to only be included when building the
`application` target and do compile-time checks to exclude certain
modules when compiling without telemetry

uses both checks against Mix.target() and checks for the presence of
dependent modules to make compilation and runtime robust when running as
docker application, local dev server and when used as a dependency

Author: magnetised

.changeset/few-trains-kick.md

@@ -0,0 +1,5 @@
+---
+"@core/sync-service": patch
+---
+
+Only include telemetry in docker build

packages/sync-service/Dockerfile

@@ -4,18 +4,21 @@ ARG DEBIAN_VERSION=bookworm-20241223-slim
 
 ARG BUILDER_IMAGE="hexpm/elixir:${ELIXIR_VERSION}-erlang-${OTP_VERSION}-debian-${DEBIAN_VERSION}"
 ARG RUNNER_IMAGE="debian:${DEBIAN_VERSION}"
+ARG MIX_TARGET=application
 
 FROM ${BUILDER_IMAGE} AS builder
 LABEL maintainer="info@electric-sql.com"
 
 RUN apt-get update -y && \
-    apt-get install -y build-essential git curl && \
-    apt-get clean && \
-    rm -f /var/lib/apt/lists/*_*
+  apt-get install -y build-essential git curl && \
+  apt-get clean && \
+  rm -f /var/lib/apt/lists/*_*
 
 RUN mix local.hex --force && mix local.rebar --force
 
-ENV MIX_ENV=prod
+ARG MIX_ENV=prod
+ARG ELECTRIC_VERSION
+ARG MIX_TARGET
 
 WORKDIR /app
 
@@ -30,38 +33,45 @@ COPY lib /app/lib/
 COPY package.json /app/
 COPY config/*.exs /app/config/
 
-ARG ELECTRIC_VERSION
 
 RUN mix compile
 RUN mix sentry.package_source_code
 RUN mix release
 
+RUN ls -l /app/_build
+
 FROM ${RUNNER_IMAGE} AS runner_setup
 
 RUN apt-get update -y && \
-    apt-get install -y libstdc++6 openssl libncurses5 locales ca-certificates curl && \
-    apt-get clean && \
-    rm -f /var/lib/apt/lists/*_*
+  apt-get install -y libstdc++6 openssl libncurses5 locales ca-certificates curl && \
+  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
+ENV LANG=en_US.UTF-8 \
+  LANGUAGE=en_US:en \
+  LC_ALL=en_US.UTF-8 \
+  MIX_ENV=prod \
+  MIX_TARGET=application
 
 WORKDIR "/app"
+
 RUN chown nobody /app
 
 FROM runner_setup AS runner
 
+ARG MIX_TARGET
 ARG RELEASE_NAME=electric
-## Vaxine configuration via environment variables
-COPY --from=builder /app/_build/prod/rel/${RELEASE_NAME} ./
-RUN mv /app/bin/${RELEASE_NAME} /app/bin/entrypoint
 
 
+COPY --from=builder "/app/_build/${MIX_TARGET}_prod/rel/${RELEASE_NAME}" ./
+
+RUN mv /app/bin/${RELEASE_NAME} /app/bin/entrypoint
+
 HEALTHCHECK --start-period=10s CMD curl --fail http://localhost:${ELECTRIC_PORT-3000}/v1/health || exit 1
 
 ENTRYPOINT ["/app/bin/entrypoint"]
+
 CMD ["start"]

packages/sync-service/lib/electric/plug/router.ex

@@ -1,6 +1,10 @@
 defmodule Electric.Plug.Router do
   use Plug.Router, copy_opts_to_assign: :config
-  use Sentry.PlugCapture
+  use Electric.Telemetry
+
+  with_telemetry Sentry.PlugCapture do
+    use Sentry.PlugCapture
+  end
 
   alias Electric.Plug.Utils.CORSHeaderPlug
   alias Electric.Plug.Utils.PassAssignToOptsPlug
@@ -16,7 +20,11 @@ defmodule Electric.Plug.Router do
   plug Electric.Plug.TraceContextPlug
   plug Plug.Telemetry, event_prefix: [:electric, :routing]
   plug Plug.Logger
-  plug Sentry.PlugContext
+
+  with_telemetry Sentry.PlugCapture do
+    plug Sentry.PlugContext
+  end
+
   plug :put_cors_headers
   plug :dispatch
 

packages/sync-service/lib/electric/plug/utility_router.ex

@@ -1,8 +1,13 @@
 defmodule Electric.Plug.UtilityRouter do
   use Plug.Router
+  use Electric.Telemetry
 
   plug :match
   plug :dispatch
 
-  get "/metrics", do: resp(conn, 200, TelemetryMetricsPrometheus.Core.scrape())
+  with_telemetry TelemetryMetricsPrometheus.Core do
+    get "/metrics", do: resp(conn, 200, TelemetryMetricsPrometheus.Core.scrape())
+  else
+    get "/metrics", do: resp(conn, 200, "[]")
+  end
 end

packages/sync-service/lib/electric/telemetry.ex

@@ -0,0 +1,40 @@
+defmodule Electric.Telemetry do
+  require Logger
+
+  @enabled Mix.env() == :test || Mix.target() == Electric.MixProject.telemetry_target()
+  @log_level Application.compile_env(:electric, [Electric.Telemetry, :log_level], false)
+
+  defmacro __using__(_opts) do
+    quote do
+      import Electric.Telemetry
+    end
+  end
+
+  # uses the availability of the given dependencies to optionally compile
+  # the provided block when MIX_TARGET is `:application`.
+  defmacro with_telemetry(dependencies, do: block, else: else_block) do
+    include_with_telemetry(__CALLER__, __ENV__, dependencies, block, else_block)
+  end
+
+  defmacro with_telemetry(dependencies, do: block) do
+    include_with_telemetry(__CALLER__, __ENV__, dependencies, block, nil)
+  end
+
+  defp include_with_telemetry(caller, env, dependencies, block, else_block) do
+    modules = List.wrap(dependencies) |> Enum.map(&Macro.expand(&1, env))
+    available? = Enum.all?(modules, &Code.ensure_loaded?/1)
+
+    if @enabled && available? do
+      if @log_level,
+        do:
+          Logger.log(
+            @log_level,
+            "Enabling telemetry in #{caller.module || Path.relative_to(caller.file, Path.expand("..", __DIR__))}"
+          )
+
+      quote(do: unquote(block))
+    else
+      if else_block, do: quote(do: unquote(else_block))
+    end
+  end
+end