Adding example for using monitr, process-watcher and mod_statuspage together

Author: rohiniwork

examples/app-highavailability/application.js

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+/*
+ * Copyright (c) 2013, Yahoo! Inc. All rights reserved.
+ * Copyrights licensed under the New BSD License.
+ * See the accompanying LICENSE file for terms.
+ */
+
+// Reference: TODO put the blog link here
+
+var cluster = require('cluster'),
+    express = require('express'),
+    http = require('http'),
+    monitor = require('monitr'),
+    status = require('mod_statuspage'),
+    timers = require('timers');
+// Spawn numCPUs worker processes
+var numCPUs = require('os').cpus().length;
+
+// Master spawns worker processes
+if (cluster.isMaster) {
+
+  // Fork workers
+  for (var i = 0; i < numCPUs; i++) {
+     console.log('Starting worker ' + i);
+     cluster.fork();
+  }
+  
+  // If any worker process dies, spawn a new one to bring back number of processes 
+  // to be back to numCPUs
+  cluster.on('exit', function(worker, code, signal) {
+     console.log('worker ' + worker.process.pid + ' died');
+     cluster.fork();
+  });
+
+  // Logs to know what workers are active
+  cluster.on('online', function (worker) {
+     console.log('Worker ' + worker.process.pid + ' online');
+  });
+
+} else {
+    // Worker process
+    // Start monitoring
+    monitor.start();
+    
+    // Simple express app
+    var app = express();
+    // Server statuspage to get application metrics
+    app.use(status({
+        url: '/status',
+        check: function(req) {
+            if (req.something == false) {
+                return false; //Don't show status
+            }
+            return true; //Show status
+        },
+        responseContentType : 'html'
+    }));
+    // An example of a request that makes CPU idle for some time
+    app.get('/late-response', function(req, res) {
+        var end = Date.now() + 5000
+        // CPU cycles wasted for 5000ms
+        // Blocking
+        while (Date.now() < end) ;
+        res.writeHead(200, {'Content-Type': 'text/plain'});
+        res.end('I came after a delay\n');
+    });
+    // All other requests served normal
+    app.get('*', function (req, res) {
+      res.writeHead(200, {'Content-Type': 'text/plain'});
+      res.end('I am being monitored\n');
+    });
+    
+    console.log('Go to: http://127.0.0.1:8000/status');
+    app.listen(8000);
+    
+    // Stop monitoring
+    process.on('exit', function () {
+       monitor.stop();
+    });
+    
+    // Graceful shutdown
+    process.on('SIGINT', function () {
+       process.exit();
+    });
+} // end worker

examples/app-highavailability/listener.js

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+/*
+ * Copyright (c) 2013, Yahoo! Inc. All rights reserved.
+ * Copyrights licensed under the New BSD License.
+ * See the accompanying LICENSE file for terms.
+ */
+// Reference : Put the blog post here
+var watcher = require('process-watcher');
+
+/*
+ * Dummy metric monitoring object.
+ */
+var watcher_metric = {
+    /**
+     * Increments metric
+     */
+    increment : function (name, v) {
+        console.log('Increment ' + name + ' with ' + v);
+    },
+    /**
+     * Set the metric or multiple metrics at the same time.
+     */
+    set : function (name, v) {
+        console.log('Setting the following metrics: ' + require('util').inspect(name));
+    }
+};
+var dgpath = '/tmp/nodejs.mon',
+    statusPath = '/tmp/watcher_status_path_test',
+    watcher_config = { max_inactive : 0.001, monitor : 0.001,  monPath: dgpath,
+        timeout : 3, timeout_start : 60 };
+
+//Instantiate watcher
+var watcher_instance = new watcher.Watcher({ metric : watcher_metric, config : watcher_config });