metrics: add stream api for system info

src/metrics.js

@@ -2,6 +2,8 @@
 
 exports = module.exports = {
     getSystem,
+    getSystemStream,
+
     getContainers,
 
     sendToGraphite
@@ -16,6 +18,7 @@ const apps = require('./apps.js'),
     execSync = require('child_process').execSync,
     net = require('net'),
     os = require('os'),
+    { Readable } = require('stream'),
     safe = require('safetydance'),
     services = require('./services.js'),
     superagent = require('./superagent.js');
@@ -226,7 +229,7 @@ async function getContainers(name, options) {
     };
 }
 
-async function getSystemStats(options) {
+async function readSystemFromGraphite(options) {
     assert.strictEqual(typeof options, 'object');
 
     const { fromSecs, intervalSecs, noNullPoints } = options;
@@ -269,7 +272,7 @@ async function getSystemStats(options) {
 async function getSystem(options) {
     assert.strictEqual(typeof options, 'object');
 
-    const systemStats = await getSystemStats(options);
+    const systemStats = await readSystemFromGraphite(options);
 
     const appStats = {};
     for (const app of await apps.list()) {
@@ -289,3 +292,32 @@ async function getSystem(options) {
         cpuCount: os.cpus().length
     };
 }
+
+async function getSystemStream() {
+    const INTERVAL_SECS = 2;
+    let intervalId = null, oldCpuMetrics = null;
+
+    const metricsStream = new Readable({
+        read(/*size*/) { /* ignored, we push via interval */ },
+        destroy(error, callback) {
+            clearInterval(intervalId);
+            callback(error);
+        }
+    });
+
+    intervalId = setInterval(async () => {
+        const memoryMetrics = await getMemoryMetrics();
+        const cpuMetrics = await getCpuMetrics();
+
+        const cpuPercent = oldCpuMetrics ? (cpuMetrics.userMsecs + cpuMetrics.sysMsecs - oldCpuMetrics.userMsecs - oldCpuMetrics.sysMsecs) * 0.1 / INTERVAL_SECS : null;
+        oldCpuMetrics = cpuMetrics;
+
+        const now = Date.now();
+        metricsStream.push(JSON.stringify({
+            cpu: [ cpuPercent, now ],
+            memory: [ memoryMetrics.used, now ]
+        }));
+    }, INTERVAL_SECS*1000);
+
+    return metricsStream;
+}