code commented

application/Dockerfile

+# Node alpine is used as base for the image. 
+# The node alpine is the lightweight version of node, that way the image stays as small in size as possible
 FROM node:lts-alpine
 ENV NODE_ENV=production
+# Here the Working directory is created and navigated to. 
+# Into this Working directory we copy the code from the local maschine to the container.
 WORKDIR /usr/src/CLOUD-COMPUTING_2022
+# Here we copy the package*.json and then install all the dependencies. 
+# The Maven folder will not be copied to the Container as its on the dockerignore list.
+# That way we ensure all dependencies are correctly set inside the container
 COPY ["package.json", "package-lock.json*", "npm-shrinkwrap.json*", "./"]
 RUN npm install --production --silent && mv node_modules ../
+# After installing the dependencies we copy the actual code into the container and expose port 3000.
 COPY . .
 EXPOSE 3000
 RUN chown -R node /usr/src/CLOUD-COMPUTING_2022
 USER node
+# When running the Image in a container the application will start
 CMD ["node", "server.js"]

application/metrics.js

 const client = require('prom-client')
 
+//creating a registry where the metrics are collected 
 const register = new client.Registry()
 
 register.setDefaultLabels({
   app: 'cloud-computing-chat'
 })
 
+//this enables collecting the defaul metrics the prom-client for node offers 
 client.collectDefaultMetrics({register})
 
-
+//here the metrics are defined 
 const msgSent = new client.Counter({
     name: 'msgSent',
     help: 'total number of messages sent'
@@ -35,13 +37,14 @@ const failedLogins = new client.Counter({
   help: 'number of failed logins'
 })
   
+//this registers the metrics in the registry we have created 
 register.registerMetric(registercounter)
 register.registerMetric(msgSent)
 register.registerMetric(msgLength)
 register.registerMetric(onlineUser)
 register.registerMetric(failedLogins)
 
-
+//exports the registry and the metrics to apply changes to metrics. e.g. inc the count for msgSent
 exports.register = register
 exports.msgSent = msgSent
 exports.msgLength = msgLength

application/server.js

@@ -88,6 +88,7 @@ app.get('/index', (req, res) => {
 io.on('connection', (socket) => {
   socket.on('chat message', (msg) => {
     Metrics.msgSent.inc()
+    //this returns the count of words for every msg sent
     var length = msg.split(' ').filter(word=> word !=='').length
     Metrics.msgLength.observe(length)
     io.emit('chat message', msg);
@@ -110,6 +111,7 @@ require(path.join(__dirname,'/app/routes/auth.routes'))(app);
 require(path.join(__dirname,'/app/routes/user.routes'))(app);
 
 
+//exporting the collected metrics to prometheus metrics endpoint 
 app.get('/metrics', async (req, res) => {
   res.set('Content-Type', Metrics.register.contentType)
   res.end(await Metrics.register.metrics())