Easily identify problems in Node.js applications with Diagnostic Report

Easily identify problems in Node.js applications with Diagnostic Report

The Diagnostic Report utility was recently brought into the Node.js core to help developers identify almost all scenarios of Node.js application anomalies in production. The scenarios include abnormal termination such as a crash, slow performance, memory leak, high CPU, unexpected errors, incorrect output, and more.

The Diagnostic Report utility was recently brought into the Node.js core to help developers identify almost all scenarios of Node.js application anomalies in production. The scenarios include abnormal termination such as a crash, slow performance, memory leak, high CPU, unexpected errors, incorrect output, and more.

While the report does not pinpoint the exact problem or specific fixes, its content-rich diagnostic data offers vital hints about the issue and accelerates the diagnostic process.

The utility was originally available as a npm module, and was brought into the Node.js core because it significantly helps identify the root cause of numerous types of problems, including support issues sent to the different repositories in the Node.js organization. Before it was part of the core, you had to explicitly add the dependency to the npm module in a users’ application, which was a blocker for adoption of the diagnostic tool.

In this blog post, I describe why this tool is important, and then go into some detail on how to interpret the report data, and towards the end of the post, walk you through some example use cases.

Common diagnostic steps

Typically, the starting point to diagnose a problem in an application is to:

  • Capture data to understand the execution environment of the deployment
  • Define a debugging strategy based on the information you obtained
  • Execute one or more investigative steps. Potentially, each step could change what you look for or do based on the inference from the previous steps
  • Iterate until the current theory is confirmed by the data captured

Problem determination of Node.js deployments involves a number of different tools and methodologies. The problem itself determines the action you take to resolve the issue.

For example, if your application crashes, you would:

  • Load the crash dump into a debugger
  • Examine the failing context in the failing thread
  • Go through the execution sequence backwards to identify what code flow or data flow led to the anomaly and what application, third party, runtime code, or configuration is responsible for the said code flow or data flow.

For an issue related to a memory leak, these steps might be different.

Problem determination problems in production-grade deployments

For production-grade deployments, the approach for diagnosing the problem that I outlined above poses a number of challenges, specifically:

  • Unintended business impact. The steps can be iterative, and if followed, can cause unacceptable impact to the business that the production system represents. Even if they’re not iterative, they can cause the debugging task to be delayed. For example, the next data capture needs to wait until the next recycle, which is weeks away.
  • Prone to human error. These diagnostic steps can be error prone depending on the skill level of the person who’s conducting them. For example, an IT admin who carries out the steps at the production site is not skilled enough with Node.js diagnostics.
  • Knowledge gaps. Many times, additional settings need to be set on the system to collect data. For example, you might have to change ulimit settings to enable a dump or enable gc logging to collect the heap statistics and gc activities.
  • Data collection limitations. Many times, the required data may not be easy or even possible to collect. Examples of hard to collect data include: How many handles were in the event loop? What states were those are in? Which SSL library the Node executable was linked against?
  • Binary data hurdles. Because the data is being collected in binary format, many times, the user or admin has no idea what debugging process is being carried out or what data is being collected. Sometimes it’s hard to gain approval for forwarding binary data to the devs who can resolve the issue versus a readable format which can more easily be reviewed and sanitized.
Solution

The solution is useful documentation that explains the most common diagnostic data that is pertinent to your specific execution environment. Diagnostic Report does this using first failure data capture (FFDC). This document is in semi man-machine readable format, so you can read it in its original state if you’re moderately skilled at diagnostics reporting or it can be loaded into a JS program or passed to a monitoring agent.

This document can improve the overall troubleshooting experience because it:

  • Answers many routine questions which can reduce the number of iterations needed to understand the cause of the failure.
  • Offers a comprehensive view of the state of the application and virtual machine at the time of failure. This information can drastically improve the decision making for the next set of data collection, if required.

Ideally, the FFDC enables someone to resolve the issue without any additional information!

Function

Diagnostic Report is an experimental tool that is built into the Node.js core. Its function is to produce a JSON document about points of application misbehavior, or at a point where the user is interested in getting more information. The document produced contains information about the state of the application and the hosting platform, covering all the vital data elements.

The following command line argument runs Diagnostic Report (there are many other ones but this is one).

$ node--experimental-report --diagnostic-report-uncaught-exception w.js

Writing Node.js report to file: report.20190309.102401.47640.001.json
Node.js report completed

Data that it captures could be related to anomalies like fatal errors that terminate the program, application exceptions, or any other common failure scenarios. The data that the tools actually captures could be JavaScript heap statistics, native and application callstack, process’ CPU consumption, and more.

A few command line arguments are available to control the report generation triggers and the report generation behaviors.

You can also generate the report explicitly via an API which is exposed through the Node.js process object. When using the API, the report is available both as a disk file or a JSON string. Another API controls the report generation triggers and reports generation behaviors.

Use cases

In this section, we illustrate some of the benefits of Diagnostic Report through a few different use cases. Keep in mind that this list isn’t exhaustive. Diagnostic Report is a general-purpose tool that can be used in any problem scenarios.

  1. Identify which SSL library the current Node installation is linked against (roughly identify the distribution).
  2. In this case, you can produce a report through the process.report.writeReport() API. As the following image shows, the component versions section contains the SSL linkage information. In this case, it is linked against version 1.1.1b of openssl (line 12).
  3. Reviewing the shared libraries that Node is linked against, you see no external SSL libraries in the list. From there, you can conclude that this is a standard community distribution.
  4. A Node application hangs when you expect it to complete some tasks and then terminate. You have no idea what is causing the event loop to engage.
  5. In this case, produce the report by sending a SIGUSR2 signal to the running process.
  6. The generated report shows an active timer handle lying in the loop that has an expiry time of around 10 hours from the current time. (You can see that on line 4; “firesinMSfromNow” shows how many milliseconds it takes to fire).
  7. Because the application should not be scheduling an event for 10 hours in the future, you now understand the reason for hang. To fix, search in the application that installs a setTimeout handler with the said duration.
  8. You to make sure a web application that you host in a cloud environment is idle outside of business hours.
  9. In this case, you again produce a report by logging into the cloud instance through SSH and sending a signal to the running process. The report generated in the persistent volume showed the resource usage section:
  10. Lines two and three show the time spent by the node process in the user space and kernel space. Because they were only a fraction of a second spent, you can be confident that the application is relatively idle, with no file system activities in the recent past.
We need your feedback

Diagnostic Report is available as an experimental feature from Node.js v11.8.0 and subsequent releases. The tool could exit the experimental status and become a stable and supported feature, based on:

  • The perceived usability in the field
  • Any fine-grained tuning that may be required at the API interface level.

Again, this is based on user feedback.

In software development, ‘feature freeze’ is the inability to refine interfaces because they are already massively used in the field and have many software abstractions built on top of them; any changes to the interfaces can break all these.

To avoid feature freeze with our Diagnostic Report tool, we ask that you evaluate this feature as soon as you get an opportunity and provide your valuable feedback directly in the Node.js Diagnostic User Feedback repo.

How to Use Express.js, Node.js and MongoDB.js

How to Use Express.js, Node.js and MongoDB.js

In this post, I will show you how to use Express.js, Node.js and MongoDB.js. We will be creating a very simple Node application, that will allow users to input data that they want to store in a MongoDB database. It will also show all items that have been entered into the database.

In this post, I will show you how to use Express.js, Node.js and MongoDB.js. We will be creating a very simple Node application, that will allow users to input data that they want to store in a MongoDB database. It will also show all items that have been entered into the database.

Creating a Node Application

To get started I would recommend creating a new database that will contain our application. For this demo I am creating a directory called node-demo. After creating the directory you will need to change into that directory.

mkdir node-demo
cd node-demo

Once we are in the directory we will need to create an application and we can do this by running the command
npm init

This will ask you a series of questions. Here are the answers I gave to the prompts.

The first step is to create a file that will contain our code for our Node.js server.

touch app.js

In our app.js we are going to add the following code to build a very simple Node.js Application.

var express = require("express");
var app = express();
var port = 3000;
 
app.get("/", (req, res) => {
  res.send("Hello World");
});
 
app.listen(port, () => {
  console.log("Server listening on port " + port);
});

What the code does is require the express.js application. It then creates app by calling express. We define our port to be 3000.

The app.use line will listen to requests from the browser and will return the text “Hello World” back to the browser.

The last line actually starts the server and tells it to listen on port 3000.

Installing Express

Our app.js required the Express.js module. We need to install express in order for this to work properly. Go to your terminal and enter this command.

npm install express --save

This command will install the express module into our package.json. The module is installed as a dependency in our package.json as shown below.

To test our application you can go to the terminal and enter the command

node app.js

Open up a browser and navigate to the url http://localhost:3000

You will see the following in your browser

Creating Website to Save Data to MongoDB Database

Instead of showing the text “Hello World” when people view your application, what we want to do is to show a place for user to save data to the database.

We are going to allow users to enter a first name and a last name that we will be saving in the database.

To do this we will need to create a basic HTML file. In your terminal enter the following command to create an index.html file.

touch index.html

In our index.html file we will be creating an input filed where users can input data that they want to have stored in the database. We will also need a button for users to click on that will add the data to the database.

Here is what our index.html file looks like.

<!DOCTYPE html>
<html>
  <head>
    <title>Intro to Node and MongoDB<title>
  <head>

  <body>
    <h1>Into to Node and MongoDB<&#47;h1>
    <form method="post" action="/addname">
      <label>Enter Your Name<&#47;label><br>
      <input type="text" name="firstName" placeholder="Enter first name..." required>
      <input type="text" name="lastName" placeholder="Enter last name..." required>
      <input type="submit" value="Add Name">
    </form>
  <body>
<html>

If you are familiar with HTML, you will not find anything unusual in our code for our index.html file. We are creating a form where users can input their first name and last name and then click an “Add Name” button.

The form will do a post call to the /addname endpoint. We will be talking about endpoints and post later in this tutorial.

Displaying our Website to Users

We were previously displaying the text “Hello World” to users when they visited our website. Now we want to display our html file that we created. To do this we will need to change the app.use line our our app.js file.

We will be using the sendFile command to show the index.html file. We will need to tell the server exactly where to find the index.html file. We can do that by using a node global call __dirname. The __dirname will provide the current directly where the command was run. We will then append the path to our index.html file.

The app.use lines will need to be changed to
app.use("/", (req, res) => {   res.sendFile(__dirname + "/index.html"); });

Once you have saved your app.js file, we can test it by going to terminal and running node app.js

Open your browser and navigate to “http://localhost:3000”. You will see the following

Connecting to the Database

Now we need to add our database to the application. We will be connecting to a MongoDB database. I am assuming that you already have MongoDB installed and running on your computer.

To connect to the MongoDB database we are going to use a module called Mongoose. We will need to install mongoose module just like we did with express. Go to your terminal and enter the following command.
npm install mongoose --save

This will install the mongoose model and add it as a dependency in our package.json.

Connecting to the Database

Now that we have the mongoose module installed, we need to connect to the database in our app.js file. MongoDB, by default, runs on port 27017. You connect to the database by telling it the location of the database and the name of the database.

In our app.js file after the line for the port and before the app.use line, enter the following two lines to get access to mongoose and to connect to the database. For the database, I am going to use “node-demo”.

var mongoose = require("mongoose"); mongoose.Promise = global.Promise; mongoose.connect("mongodb://localhost:27017/node-demo");

Creating a Database Schema

Once the user enters data in the input field and clicks the add button, we want the contents of the input field to be stored in the database. In order to know the format of the data in the database, we need to have a Schema.

For this tutorial, we will need a very simple Schema that has only two fields. I am going to call the field firstName and lastName. The data stored in both fields will be a String.

After connecting to the database in our app.js we need to define our Schema. Here are the lines you need to add to the app.js.
var nameSchema = new mongoose.Schema({   firstName: String,   lastNameName: String });

Once we have built our Schema, we need to create a model from it. I am going to call my model “DataInput”. Here is the line you will add next to create our mode.
var User = mongoose.model("User", nameSchema);

Creating RESTful API

Now that we have a connection to our database, we need to create the mechanism by which data will be added to the database. This is done through our REST API. We will need to create an endpoint that will be used to send data to our server. Once the server receives this data then it will store the data in the database.

An endpoint is a route that our server will be listening to to get data from the browser. We already have one route that we have created already in the application and that is the route that is listening at the endpoint “/” which is the homepage of our application.

HTTP Verbs in a REST API

The communication between the client(the browser) and the server is done through an HTTP verb. The most common HTTP verbs are
GET, PUT, POST, and DELETE.

The following table explains what each HTTP verb does.

HTTP Verb Operation
GET Read
POST Create
PUT Update
DELETE Delete

As you can see from these verbs, they form the basis of CRUD operations that I talked about previously.

Building a CRUD endpoint

If you remember, the form in our index.html file used a post method to call this endpoint. We will now create this endpoint.

In our previous endpoint we used a “GET” http verb to display the index.html file. We are going to do something very similar but instead of using “GET”, we are going to use “POST”. To get started this is what the framework of our endpoint will look like.

app.post("/addname", (req, res) => {
 
});
Express Middleware

To fill out the contents of our endpoint, we want to store the firstName and lastName entered by the user into the database. The values for firstName and lastName are in the body of the request that we send to the server. We want to capture that data, convert it to JSON and store it into the database.

Express.js version 4 removed all middleware. To parse the data in the body we will need to add middleware into our application to provide this functionality. We will be using the body-parser module. We need to install it, so in your terminal window enter the following command.

npm install body-parser --save

Once it is installed, we will need to require this module and configure it. The configuration will allow us to pass the data for firstName and lastName in the body to the server. It can also convert that data into JSON format. This will be handy because we can take this formatted data and save it directly into our database.

To add the body-parser middleware to our application and configure it, we can add the following lines directly after the line that sets our port.

var bodyParser = require('body-parser');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
Saving data to database

Mongoose provides a save function that will take a JSON object and store it in the database. Our body-parser middleware, will convert the user’s input into the JSON format for us.

To save the data into the database, we need to create a new instance of our model that we created early. We will pass into this instance the user’s input. Once we have it then we just need to enter the command “save”.

Mongoose will return a promise on a save to the database. A promise is what is returned when the save to the database completes. This save will either finish successfully or it will fail. A promise provides two methods that will handle both of these scenarios.

If this save to the database was successful it will return to the .then segment of the promise. In this case we want to send text back the user to let them know the data was saved to the database.

If it fails it will return to the .catch segment of the promise. In this case, we want to send text back to the user telling them the data was not saved to the database. It is best practice to also change the statusCode that is returned from the default 200 to a 400. A 400 statusCode signifies that the operation failed.

Now putting all of this together here is what our final endpoint will look like.

app.post("/addname", (req, res) => {
  var myData = new User(req.body);
  myData.save()
    .then(item => {
      res.send("item saved to database");
    })
    .catch(err => {
      res.status(400).send("unable to save to database");
    });
});
Testing our code

Save your code. Go to your terminal and enter the command node app.js to start our server. Open up your browser and navigate to the URL “http://localhost:3000”. You will see our index.html file displayed to you.

Make sure you have mongo running.

Enter your first name and last name in the input fields and then click the “Add Name” button. You should get back text that says the name has been saved to the database like below.

Access to Code

The final version of the code is available in my Github repo. To access the code click here. Thank you for reading !

Node.js for Beginners - Learn Node.js from Scratch (Step by Step)

Node.js for Beginners - Learn Node.js from Scratch (Step by Step)

Node.js for Beginners - Learn Node.js from Scratch (Step by Step) - Learn the basics of Node.js. This Node.js tutorial will guide you step by step so that you will learn basics and theory of every part. Learn to use Node.js like a professional. You’ll learn: Basic Of Node, Modules, NPM In Node, Event, Email, Uploading File, Advance Of Node.

Node.js for Beginners

Learn Node.js from Scratch (Step by Step)

Welcome to my course "Node.js for Beginners - Learn Node.js from Scratch". This course will guide you step by step so that you will learn basics and theory of every part. This course contain hands on example so that you can understand coding in Node.js better. If you have no previous knowledge or experience in Node.js, you will like that the course begins with Node.js basics. otherwise if you have few experience in programming in Node.js, this course can help you learn some new information . This course contain hands on practical examples without neglecting theory and basics. Learn to use Node.js like a professional. This comprehensive course will allow to work on the real world as an expert!
What you’ll learn:

  • Basic Of Node
  • Modules
  • NPM In Node
  • Event
  • Email
  • Uploading File
  • Advance Of Node

Top 7 Most Popular Node.js Frameworks You Should Know

Top 7 Most Popular Node.js Frameworks You Should Know

Node.js is an open-source, cross-platform, runtime environment that allows developers to run JavaScript outside of a browser. In this post, you'll see top 7 of the most popular Node frameworks at this point in time (ranked from high to low by GitHub stars).

Node.js is an open-source, cross-platform, runtime environment that allows developers to run JavaScript outside of a browser.

One of the main advantages of Node is that it enables developers to use JavaScript on both the front-end and the back-end of an application. This not only makes the source code of any app cleaner and more consistent, but it significantly speeds up app development too, as developers only need to use one language.

Node is fast, scalable, and easy to get started with. Its default package manager is npm, which means it also sports the largest ecosystem of open-source libraries. Node is used by companies such as NASA, Uber, Netflix, and Walmart.

But Node doesn't come alone. It comes with a plethora of frameworks. A Node framework can be pictured as the external scaffolding that you can build your app in. These frameworks are built on top of Node and extend the technology's functionality, mostly by making apps easier to prototype and develop, while also making them faster and more scalable.

Below are 7of the most popular Node frameworks at this point in time (ranked from high to low by GitHub stars).

Express

With over 43,000 GitHub stars, Express is the most popular Node framework. It brands itself as a fast, unopinionated, and minimalist framework. Express acts as middleware: it helps set up and configure routes to send and receive requests between the front-end and the database of an app.

Express provides lightweight, powerful tools for HTTP servers. It's a great framework for single-page apps, websites, hybrids, or public HTTP APIs. It supports over fourteen different template engines, so developers aren't forced into any specific ORM.

Meteor

Meteor is a full-stack JavaScript platform. It allows developers to build real-time web apps, i.e. apps where code changes are pushed to all browsers and devices in real-time. Additionally, servers send data over the wire, instead of HTML. The client renders the data.

The project has over 41,000 GitHub stars and is built to power large projects. Meteor is used by companies such as Mazda, Honeywell, Qualcomm, and IKEA. It has excellent documentation and a strong community behind it.

Koa

Koa is built by the same team that built Express. It uses ES6 methods that allow developers to work without callbacks. Developers also have more control over error-handling. Koa has no middleware within its core, which means that developers have more control over configuration, but which means that traditional Node middleware (e.g. req, res, next) won't work with Koa.

Koa already has over 26,000 GitHub stars. The Express developers built Koa because they wanted a lighter framework that was more expressive and more robust than Express. You can find out more about the differences between Koa and Express here.

Sails

Sails is a real-time, MVC framework for Node that's built on Express. It supports auto-generated REST APIs and comes with an easy WebSocket integration.

The project has over 20,000 stars on GitHub and is compatible with almost all databases (MySQL, MongoDB, PostgreSQL, Redis). It's also compatible with most front-end technologies (Angular, iOS, Android, React, and even Windows Phone).

Nest

Nest has over 15,000 GitHub stars. It uses progressive JavaScript and is built with TypeScript, which means it comes with strong typing. It combines elements of object-oriented programming, functional programming, and functional reactive programming.

Nest is packaged in such a way it serves as a complete development kit for writing enterprise-level apps. The framework uses Express, but is compatible with a wide range of other libraries.

LoopBack

LoopBack is a framework that allows developers to quickly create REST APIs. It has an easy-to-use CLI wizard and allows developers to create models either on their schema or dynamically. It also has a built-in API explorer.

LoopBack has over 12,000 GitHub stars and is used by companies such as GoDaddy, Symantec, and the Bank of America. It's compatible with many REST services and a wide variety of databases (MongoDB, Oracle, MySQL, PostgreSQL).

Hapi

Similar to Express, hapi serves data by intermediating between server-side and client-side. As such, it's can serve as a substitute for Express. Hapi allows developers to focus on writing reusable app logic in a modular and prescriptive fashion.

The project has over 11,000 GitHub stars. It has built-in support for input validation, caching, authentication, and more. Hapi was originally developed to handle all of Walmart's mobile traffic during Black Friday.