updated docker file

Dockerfile

-FROM node:8.11.3-alpine
+FROM node:8.11-alpine
 
+# Install CURL which is used for healthcheck
 RUN apk add --no-cache curl
 
+# Set work directory
 WORKDIR /usr/src/app
 
-RUN npm install pm2 -g
+# Install pm2 to manage the node process
+RUN npm install pm2@2 -g
 
+# Download application dependencies
 RUN npm install
 
+# Expose application port
 EXPOSE 3000
+
+# Expose application debug port
 EXPOSE 9232
 
+# start node.js application with pm2
 CMD ["pm2", "start", "processes.json", "--no-daemon"]
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