diff --git a/example-1/Dockerfile b/example-1/Dockerfile
index ecf93e0..265a42d 100644
--- a/example-1/Dockerfile
+++ b/example-1/Dockerfile
@@ -1,8 +1,9 @@
 FROM node:12.18.1-alpine
-
+#  in case that you want to set the port number in the image and not in the app uncomment by removing # sign from below line.
+# ENV PORT=3000
 WORKDIR /usr/src/app
 COPY package*.json ./
 RUN npm install --only=production
 COPY ./src ./src
 COPY ./videos ./videos
-CMD npm start
\ No newline at end of file
+CMD npm start