add healthcheck

backend/CHECKS

@@ -0,0 +1 @@
+/health OK

backend/Dockerfile

@@ -46,6 +46,7 @@ ENV APP_NAME=backend
 
 COPY --from=build /app/_build/prod/rel/${APP_NAME} ./
 COPY Procfile ./
+COPY CHECKS ./
 RUN chown -R nobody: /app
 USER nobody
 

backend/lib/backend_web/endpoint.ex

@@ -1,6 +1,8 @@
 defmodule BackendWeb.Endpoint do
   use Phoenix.Endpoint, otp_app: :backend
 
+  plug BackendWeb.Healthcheck
+
   socket("/socket", BackendWeb.UserSocket,
     websocket: true,
     longpoll: false

backend/lib/backend_web/healthcheck.ex

@@ -0,0 +1,13 @@
+defmodule BackendWeb.Healthcheck do
+  import Plug.Conn
+
+  def init(opts), do: opts
+
+  def call(%Plug.Conn{request_path: "/health"} = conn, _opts) do
+    conn
+    |> send_resp(200, "OK")
+    |> halt()
+  end
+
+  def call(conn, _opts), do: conn
+end