Create a multi-container app

data/.dockerignore

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+node_modules

data/Dockerfile.template

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+FROM balenalib/%%BALENA_MACHINE_NAME%%-debian-node:10-stretch-run
+
+WORKDIR /usr/src/app
+
+COPY package*.json ./
+
+RUN JOBS=MAX npm install --production
+COPY . ./
+
+CMD ["npm", "start"]

data/index.js

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+const express = require('express');
+const app = express();
+const server = require('http').createServer(app);
+const io = require('socket.io')(server);
+const { exec } = require('child_process');
+
+server.listen(8080);
+
+const getCpuLoad = socket => exec('cat /proc/loadavg', (err, text) => {
+  if (err) {
+    throw err;
+  }
+
+  // Get overall load average from the last minute
+  const matchLoad = text.match(/(\d+\.\d+)\s+/);
+
+  if (matchLoad) {
+    const load = parseFloat(matchLoad[1]);
+    socket.emit('loadavg', { onemin: load });
+  }
+});
+
+const getMemoryInfo = socket => exec('cat /proc/meminfo', (err, text) => {
+  if (err) {
+    throw err;
+  }
+
+  const matchTotal = text.match(/MemTotal:\s+([0-9]+)/);
+  const matchFree = text.match(/MemFree:\s+([0-9]+)/);
+
+  if (matchTotal && matchFree) {
+    const total = parseInt(matchTotal[1], 10);
+    const free = parseInt(matchFree[1], 10);
+    const percentageUsed = (total - free) / total * 100;
+    socket.emit('memory', { used: percentageUsed });
+  }
+});
+
+io.on('connection', socket => {
+  console.log('A user connected!');
+
+  let dataloop = setInterval(() => {
+    getCpuLoad(socket);
+    getMemoryInfo(socket);
+  }, 1000);
+
+  socket.on('disconnect', () => {
+    console.log('A user disconnected.');
+    clearInterval(dataloop);
+  });
+});