Senior Software Engineer with 10 years of experience in full-stack development, and holding a Programming in HTML5 with JavaScript and CSS3 Certification (Issued by Microsoft), creating interactive web pages (HTML5, JavaScript, CSS3), and User Experience (UX) development. Expertise designing systems, leveraging agile & scrum practices, and developing Customer Relationship Management (CRM) systems. Keen on understanding of design patterns, microservices architecture, object-oriented programming. Constantly improving experience developing with JavaScript (or TypeScript or any other flavor of the language) on the back-end.

About Me

Volodymyr Loban


Some time ago I started to create a popular match 3 game. It was very exiting because of very begging of my career, that I have made a pause for long time and now I decided to check how it works and share my experience. So we will need 5 steps for it:

## Setup the Game Canvas and Grid:
I pick CreateJS library to save some space and focus on developing game and not fighting with Canvas. We will create canvas and game field with grid. I managed grid with CSS.

```css
#fieldGrid {
    display: block;
    margin: auto;
    background-image: url('../img/bg.png');
}
```
![Setup grid](/assets/jewels/field.png)

## Generate and Render Initial Level:
Pretty easy, we will need an initial jewel generator:

```typescript
function GenerateNewJewel(i, j) {
  const r = Math.floor(Math.random() * INDEX_RANDOM) % images.length;
  const bitmap = new createjs.Bitmap(loader.getResult(images[r].id));
  const hit = new createjs.Shape();

  hit.graphics.beginFill(COLOR_BLACK).drawRect(0, 0, bitmap.getBounds().width, bitmap.getBounds().height);

  [bitmap.x, bitmap.y] = [j * 100 | 0, i * 100 | 0];
  [bitmap.CoordinateX, bitmap.CoordinateY] = [j, i];

  bitmap.hitArea = hit;
  bitmap.name = images[r].id;
  bitmap.cursor = "pointer";
  bitmap.addEventListener('click', jewelClick);

  return bitmap;
}
```
and fill the level:
```typescript
function fillLevel() {
  for (let i = 0; i < 8; i++) {
    const container = new createjs.Container();
    for (let j = 0; j < 8; j++) {
      container.addChild(new GenerateNewJewel(i, j));
    }
    stage.addChild(container);
  }
}

```
![Application Architecture](/assets/jewels/fill-level.png)

## Implement User Interaction:
It is a little bit more complex because of data manipulation and data manipulation. We will need to switch element in our elements in matrix and handle animation effect:

```typescript
function replaceJewels(target, select) {
  const selectedCoordinateX = select[0].CoordinateX;
  const selectedCoordinateY = select[0].CoordinateY;
  const targetCoordinateX = target.CoordinateX;
  const targetCoordinateY = target.CoordinateY;

  createjs.Tween.get(select[0], {loop: false}, true)
    .to({x: targetCoordinateX * 100, y: targetCoordinateY * 100}, JEM_SWITCH_TIME, createjs.Ease.Ease);

  createjs.Tween.get(target, {loop: false}, true)
    .to({x: selectedCoordinateX * 100, y: selectedCoordinateY * 100}, JEM_SWITCH_TIME, createjs.Ease.Ease)
    .call(function () {
      select[0].CoordinateX = targetCoordinateX;
      select[0].CoordinateY = targetCoordinateY;
      target.CoordinateX = selectedCoordinateX;
      target.CoordinateY = selectedCoordinateY;

      stage.children[target.CoordinateY].children[target.CoordinateX] = target;
      stage.children[select[0].CoordinateY].children[select[0].CoordinateX] = select[0];

      if (!checkStage()) {
        setTimeout(() => {
          replaceJewelsBack(target, select, targetCoordinateX, targetCoordinateY, selectedCoordinateX, selectedCoordinateY);
        }, JEM_SWITCH_TIMEOUT);
      }
    });
}
```
I use timeouts for better user experience, you can successfully remove them, nothing will brake.

![Application Architecture](/assets/jewels/replace-jewels.gif)

## Match Detection and Jewel Removal:

This is one of the most interesting parts, we need to scan matrix for more match 3. Implement logic to detect matches of three or more identical jewels in a row or column. Remove matched jewels from the grid. Update the grid accordingly (e.g., shift jewels down to fill empty spaces).

```typescript

function checkStage() {
  const result = [];
  if (!stage?.children) return;
  checkRowsAndCols(stage, result)

  if (result.length !== 0) {
    score += new Set(result.flat()).size;
    updateScore(score)

    slideDownJewels(result);
    setTimeout(() => {
      stage.addEventListener("tick", checkStage);
    }, TIMEOUT)

    return true;
  }

  stage.removeEventListener("tick", checkStage);

  return false;
}

```

![Application Architecture](/assets/jewels/slide-jewels.png)

## Score Tracking and Game Loop:
Implement score tracking logic based on the number of jewels removed in each move is pretty simple. Check for available moves or grid states that allow moves is the most interesting part and has a lot of options.

![Application Architecture](/assets/jewels/score.png)
If no moves are possible, end the game or shuffle the grid to create new matches (Game Over for this example).
Feel free to mplement a game loop to continuously update the game state and render changes.

Remember, this is a simplified overview, and building a full-fledged Bejeweled game can involve more complex features like special jewel types, animations, sound effects, levels, and more. Additionally, you'll need to consider performance optimizations, user interface design, and cross-browser compatibility if you're building for the web.

The full code can be found [here](https://github.com/nutman/jewels)

Play the game you can [here](https://htmlpreview.github.io/?https://github.com/nutman/jewels/blob/master/index.html)


Create a match 3 game in 300 lines

In the previous [article](https://medium.com/@vloban/node-js-and-high-load-part-1-ba023806e72d), I provided an overview
of how high-load works in general. Now, we will take a closer look at how it looks when using Node.js. I will keep the
same sequence of chapters.

## Application Architecture:

It is important to use specific tools for specific tasks, such as using a screwdriver or saw for construction jobs
instead of a Swiss army knife. Let’s create a dedicated microservice using Node.js:

```typescript
// Import required modules
const express = require('express');

// Create an instance of Express
const app = express();

// Define a route for the microservice
app.get('/microservice', (req, res) => {
// Perform some logic for the microservice
  const data = {
    message: 'Response from the dedicated microservice',
    timestamp: new Date()
  };

  // Send the response
  res.json(data);
});

// Define the port number
const port = process.env.PORT || 4000;

// Start the server
app.listen(port, () => {
  console.log(`Microservice is running on port ${port}`);
});
```

We can create as many microservices as needed, and each one will be responsible for specific tasks.Now that we have the tools, who will use them ? Our construction worker, also known as the server, will use them:

```typescript
// Import required modules
const express = require('express');
const axios = require('axios');

// Create an instance of Express (like we did it before)
const app = express();

// Define routes where we will use microservice
app.get('/microservice-route', (req, res) => {
// Call Microservice
  axios.get('http://localhost:4000/microservice')
    .then(response => {
// Handle response from Microservice 1
      res.send(response.data);
    })
    .catch(error => {
// Handle error
      console.error('Error calling Microservice', error);
      res.status(500).send('Error calling Microservice');
    });
});

// Define a main route just to have it like general entrance
app.get('/', (req, res) => {
  res.send('Welcome to the server');
});

// Define the port number
const port = process.env.PORT || 3000;

// Start the server
app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});
```

We can now easily expand the app without worrying about any complex calculations that could potentially cause the main
server to stop working. Even if some operations fail, the main server will keep functioning. It’s worth noting that we
have a more affordable version of a separate microservice, such as a lambda function, worker, or cluster. Each option is
suitable for specific use cases.

## Load Balancing

This section is not about Node.js. Instead, we will run multiple instances of our Node.js application, configure Nginx
as a reverse proxy, configure load balancing in Nginx, and that’s it:

```typescript
http
{
  upstream
  nodejs_servers
  {
    server
    localhost:3000;
    server
    localhost:3001;
  }

  server
  {
    listen
    80;

    location / {
      proxy_pass http
  ://nodejs_servers;
    proxy_http_version
    1.1;
    proxy_set_header
    Upgrade
    $http_upgrade;
    proxy_set_header
    Connection
    'upgrade';
    proxy_set_header
    Host
    $host;
    proxy_cache_bypass
    $http_upgrade;
  }
  }
}
```

upstream nodejs_servers — defines a group of backend Node.js servers.
proxy_pass http://nodejs_servers — forwards incoming requests to one of the backend servers defined in the upstream
block.

## Horizontal Scaling

Horizontal scaling in Node.js involves adding more instances of your Node.js application across multiple servers to
handle increased traffic, improve performance, and ensure high availability. There are two main points to consider when
scaling horizontally in Node.js:

Stateless Architecture: The design of your Node.js application should be stateless or manage state externally. This
ensures that requests can be routed to any instance without relying on session affinity. External resources will be
needed for storing and managing stateful data.
Performance Optimization: It is essential to identify performance bottlenecks in your application and optimize them.
This may involve optimizing database queries, reducing I/O operations, caching frequently accessed data, or using
asynchronous operations to handle concurrency efficiently.

## Optimized Networking

“Optimized Networking” does not only refer to Node.js being used in high load scenarios. Although Node.js is efficient
at handling networking tasks, optimizing networking involves many aspects beyond just the Node.js application layer.

Optimized networking includes all the components and configurations involved in communication between different parts of
your application, external services, and end-users.

## Memory Caching

Caching is a useful method to improve performance and reduce latency for frequently accessed data. There are various
tools available for caching like npm modules or third-party solutions such as Redis or Memcached. For instance, Redis
can be used to cache data:

```typescript
// Import required modules
const express = require('express');
const redis = require('redis');

// Create an instance of Express
const app = express();

// Create a Redis client
const redisClient = redis.createClient({
  host: 'localhost', // Redis server host
  port: 6379, // Redis server port
// Add other Redis client options as needed
});

// Middleware to handle caching
const cacheMiddleware = (req, res, next) => {
  const userId = req.params.id;

  // Check if data is present in Redis cache
  redisClient.get(userId, (err, cachedData) => {
    if (err) {
      console.error('Error fetching from Redis cache:', err);
      return next();
    }

    if (cachedData !== null) {
      // Data found in cache, return cached data
      console.log('Data found in Redis cache:', cachedData);
      return res.json(JSON.parse(cachedData));
    }

    // Data not found in cache, continue to next middleware
    next();
  });
};

// Define a route to fetch user data
app.get('/user/:id', cacheMiddleware, (req, res) => {
  const userId = req.params.id;

  // Simulate fetching user data from a database or external API
  // For demonstration, generate mock user data
  const userData = {
    id: userId,
    name: `User ${userId}`,
    email: `user${userId}@example.com`
  };

  // Store fetched data in Redis cache with a TTL (time-to-live) of 5 minutes
  redisClient.setex(userId, 300, JSON.stringify(userData));

  // Return fetched user data
  console.log('Data not found in cache, fetching from source:', userData);
  res.json(userData);
});

// Define the port number
const port = process.env.PORT || 3000;

// Start the server
app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});
```

## Database Optimization

From a Node.js perspective, I would like to list some options for optimizing the database:

Optimize database queries by identifying slow ones with tools like query analyzers or ORMs and ensuring they utilize
indexes effectively.
Implementing connection pooling can improve database connection efficiency by reducing overhead of establishing and
tearing down connections for each request thereby reducing latency and increasing throughput.
Group multiple database operations into a single transaction or batch to minimize round-trips and improve efficiency.
It is recommended to use asynchronous database drivers or libraries in Node.js applications to handle database
operations asynchronously. This allows the application to continue processing other tasks while waiting for database
responses, thereby improving concurrency and performance.
It is recommended to utilize asynchronous database drivers or libraries in Node.js applications to handle database
operations asynchronously. Doing so allows the application to continue processing other tasks while waiting for database
responses, thereby improving concurrency and performance.

Non-Optimized Query:

```sql
SELECT *
FROM users
WHERE username = 'example_user';
```

Optimized Query:

```sql
SELECT id, username, email
FROM users
WHERE username = 'example_user';
```

In this optimized query, we have specified only the essential columns (id, username, email) from the users table that
need to be retrieved. By selecting only the necessary columns, we can reduce the amount of data that needs to be
transferred between the database and the application. As a result, this improves the query performance significantly.

## Performance Optimization

In my experience, optimizing performance depends on the unique case at hand. However, there are some general steps that
can be taken to avoid mistakes. Firstly, use efficient data structures and algorithms to minimize time and space
complexity. Secondly, profile your code to identify performance bottlenecks and optimize critical sections. Thirdly,
always check the dependencies you are using. Fourthly, review and optimize middleware functions to minimize overhead and
improve performance. Lastly, monitor memory usage and avoid memory leaks by properly managing resources, closing
connections, and releasing memory when it is no longer needed.

## Asynchronous Processing

In handling high-load scenarios in Node.js, it’s crucial to employ a combination of approaches for asynchronous
processing. Utilize event-driven architecture, leveraging Node.js’s EventEmitter or frameworks like Socket.IO or
RabbitMQ for efficient event-based communication. Opt for non-blocking I/O operations to prevent event loop blockages,
while embracing Promises and async/await syntax for more readable asynchronous code. Implement concurrency control
mechanisms such as connection pooling and request throttling, and break down tasks for parallel processing using
Node.js’s cluster module or worker threads. Integrate a message queue system like RabbitMQ or Kafka for queue-based
processing, prioritizing tasks and managing retries. Offload long-running tasks to background jobs or worker processes
with tools like Bull or Agenda, and ensure robust error handling and monitoring for graceful error recovery and scaling
decisions based on performance metrics.

And some code with RabbitMQ usage to reflect the slide:

Send to the queue:

```typescript
import amqp from 'amqplib/callback_api';

amqp.connect('amqp://localhost', (error0, connection) => {
  if (error0) {
    throw error0;
  }
  connection.createChannel((error1, channel) => {
    if (error1) {
      throw error1;
    }
    const queue = 'hello';
    const msg = 'Hello World!';
    channel.assertQueue(queue, {
      durable: false
    });
    channel.sendToQueue(queue, Buffer.from(msg));
    console.log(" [x] Sent %s", msg);
  });
  setTimeout(() => {
    connection.close();
    process.exit(0);
  }, 500);
});
```

Receive from the queue:

```typescript
import * as amqp from 'amqplib/callback_api';

amqp.connect('amqp://localhost', (error0: Error, connection: amqp.Connection) => {
  if (error0) {
    throw error0;
  }
  connection.createChannel(function (error1: Error, channel: amqp.Channel) {
    if (error1) {
      throw error1;
    }
    const queue = 'hello';
    channel.assertQueue(queue, {
      durable: false
    });
    console.log(" [*] Waiting for messages in %s. To exit press CTRL+C", queue);
    channel.consume(queue, (msg: amqp.Message) => {
      console.log(" [x] Received %s", msg.content.toString());
    }, {
      noAck: true
    });
  });
});
```

## Monitoring and Alerting

To effectively monitor a high-load Node.js application, it is important to collect key metrics such as CPU usage, memory
consumption, and response times. You can use tools such as Prometheus or New Relic to gather these metrics. It is also
recommended to implement structured logging for detailed event capture, and send logs to platforms such as
Elasticsearch. To visualize the collected metrics, you can set up real-time dashboards using Grafana. Additionally, it
is important to define alerting rules for timely issue detection via Slack or email. Conducting performance profiling
can help you identify bottlenecks, while integrating error tracking with tools like Sentry can aid in analysis.

```typescript
const prometheus = require('prom-client');

// Enable collection of default metrics
prometheus.collectDefaultMetrics();

function metricsMiddleware(req, res, next) {
  if (req.path === '/metrics') {
    res.set('Content-Type', prometheus.register.contentType);
    return res.end(prometheus.register.metrics());
  }
  next();
}
```

Don’t forget to set up the alerting system. I decided not to bother you with the .yml configuration file.

## Security and Compliance

Securing a Node.js application involves implementing measures such as authentication, input validation, security
headers, dependency updates, data encryption, incident response, and continuous improvement to ensure compliance with
security standards.

And some code examples.

Authorization:

```typescript
import jwt from 'jsonwebtoken';

const secret = "secret";

function authorize(req: any, res: any, next: any) {
  const token = req.headers['authorization'];
  if (!token) {
    return res.status(401).json({message: 'Access denied. No token provided.'});
  }
  jwt.verify(token, secret, (err: any, decoded: any) => {
    if (err) {
      return res.status(403).json({message: 'Invalid token.'});
    }
    req.user = decoded;
    next();
  });
}

export default authorize;
```

Validation:

```typescript
import { Request, Response, NextFunction } from 'express';
import { validationResult, Result } from 'express-validator';

function validateInputs(req: Request, res: Response, next: NextFunction): void {
  const errors: Result = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(400).json({errors: errors.array()});
  }
  next();
}

export default validateInputs;
```

Encryption:

```typescript
const crypto = require('crypto');
const encryptionKey = 'encryptionKey';

// Function to encrypt data
function encryptData(data) {
  const cipher = crypto.createCipher('aes-256-cbc', encryptionKey);
  let encryptedData = cipher.update(data, 'utf8', 'hex');
  encryptedData += cipher.final('hex');
  return encryptedData;
}

// Function to decrypt data
function decryptData(encryptedData) {
  const decipher = crypto.createDecipher('aes-256-cbc', encryptionKey);
  let decryptedData = decipher.update(encryptedData, 'hex', 'utf8');
  decryptedData += decipher.final('utf8');
  return decryptedData;
}

// Example usage
const sensitiveData = 'This is my sensitive data';
const encrypted = encryptData(sensitiveData);
console.log('Encrypted:', encrypted);

const decrypted = decryptData(encrypted);
// Check result of encryption
console.log('Decrypted:', decrypted);
```

Conclusion:

Here is an overview of the technical aspects related to Node.js. When discussing performance and efficiency, it can be
challenging because it depends not only on the requests per second (RPS), but also on the number of connections and
latency. Additionally, the unique business logic of each project can also impact the performance of our high load
system. For now, I will not combine everything together, but I may do so in the next chapter.


Node.js and High Load (Part 2)


I will try to explain how to design a high-load system capable of handling 100,000–1,000,000 requests per second (RPS) using Node.js. It requires a robust architecture, efficient resource utilization, and careful optimization. Below is an outline of how we could design such a system in ten points:

## Application Architecture:
A microservices architecture allows for the decomposition of your application into smaller, more manageable components, fostering easier development, deployment, and scalability. With Node.js’s event-driven, non-blocking model, handling a large number of concurrent connections across these services becomes more efficient and scalable. This approach promotes flexibility, resilience, and ease of maintenance as individual services can be updated or replaced without impacting the entire system. Additionally, microservices enable teams to work independently on different parts of the application, accelerating development cycles and improving agility.

![Application Architecture](/assets/application-architecture.png)

## Load Balancing
A high-performance load balancer, like Nginx or AWS Elastic Load Balancer, is necessary to ensure that incoming traffic is evenly distributed among multiple instances of your Node.js application. Advanced load balancing algorithms, such as least connections or consistent hashing, further optimize distribution, preventing overloading on any single instance and ensuring high availability. Load balancers also play a crucial role in routing traffic away from unhealthy or overloaded nodes, maintaining smooth operation even during peak loads. This approach improves the reliability and scalability of your system, enabling it to handle varying levels of traffic efficiently.

![Application Architecture](/assets/load-balancing.png)

## Horizontal Scaling
Horizontal scaling involves adding more instances of your Node.js services across multiple servers, containers, or serverless environments to handle increased load. Utilizing container orchestration platforms like Kubernetes or serverless solutions like AWS Lambda enables automatic scaling based on demand, ensuring that resources are dynamically allocated as needed. This scalability strategy allows your system to accommodate fluctuations in traffic, maintain performance, and minimize downtime without manual intervention. By horizontally scaling your application, you can effectively handle spikes in traffic, improve fault tolerance, and ensure seamless scalability as your user base grows.

![Application Architecture](/assets/horizontal-scaling.png)

## Optimized Networking
Optimizing network configurations can help you in minimizing latency, maximizing throughput, and efficiently handling the high volume of internet traffic. By fine-tuning settings like TCP/IP stack parameters, connection timeouts, and keep-alive intervals, you can decrease unnecessary overhead and enhance the overall responsiveness of your system. Additionally, taking advantage of content delivery networks (CDNs) to cache and serve static assets closer to end-users not only reduces latency but also offloads traffic from your origin servers, improving the overall performance and scalability of your application. Optimized networking ensures that your application can efficiently handle the demands of high traffic loads while providing a smooth and enjoyable user experience.

![Application Architecture](/assets/optimized-networking.png)

## In-Memory Caching
Implementing in-memory caching using solutions like Redis or Memcached can store frequently accessed data in memory, which reduces the need to fetch it from the database repeatedly. As a result, it can reduce database load, improve response times, and enhance scalability, especially for read-heavy workloads. Distributed caching solutions can further enhance scalability by allowing caching across multiple nodes, ensuring high availability and fault tolerance. By strategically caching data at various layers of your application stack, you can optimize performance and deliver a smoother user experience.

![Application Architecture](/assets/in-memory-caching.png)

## Database Optimization
When selecting a database system, it is important to choose one that can efficiently handle high throughput and concurrent connections. Good options for this include MongoDB, PostgreSQL, or distributed databases like Cassandra. You can optimize your database by minimizing response times, reducing the load on database servers, and improving queries, indexes, and configurations. By scaling databases horizontally using techniques like sharding, you can distribute data across multiple nodes to further improve performance and scalability. With proper database optimization, you can ensure that it can handle high traffic while still maintaining data integrity and consistency.

![Application Architecture](/assets/database-optimization.png)

## Performance Optimization
To ensure that your Node.js application runs smoothly, it is important to optimize it for CPU and memory usage, reduce blocking operations, and enhance code execution paths. Techniques such as connection pooling, request batching, and streaming responses can help improve performance and resource utilization. Since Node.js operates in a single-threaded event loop, it is crucial to optimize CPU and memory usage to increase throughput and reduce response times. Regular performance testing and tuning can help identify and address bottlenecks, ensuring that your application performs optimally even under high loads.

![Application Architecture](/assets/performance-optimization.png)

## Asynchronous Processing
To ensure your Node.js instances remain responsive, offload resource-intensive or long-running tasks to background processes, worker threads, or external services. Utilizing message queues like RabbitMQ or Kafka for asynchronous processing and decoupling of components can be beneficial. By separating synchronous and asynchronous tasks, you can enhance the scalability and responsiveness of your application. Asynchronous processing enables your Node.js instances to handle incoming requests more efficiently, minimizing delays and disruptions experienced by users.

![Application Architecture](/assets/asynchronous-processing.png)

## Monitoring and Alerting
It is essential to have a comprehensive monitoring and alerting system in place to keep track of your system’s health, behavior, and performance in real-time. You can efficiently use metrics, logs, and distributed tracing to identify and troubleshoot performance bottlenecks in advance. There are many monitoring tools available like Prometheus, Grafana, and ELK stack, which can give you valuable insights into system performance and help you detect any issues before they impact users. By setting up alerts for crucial performance metrics, you can quickly respond to any anomalies and ensure the reliability and availability of your system.

![Application Architecture](/assets/monitoring-and-alerting.png)

## Security and Compliance
It is essential to implement robust security measures to protect your application from common threats such as data breaches, unauthorized access, and service interruptions. You can achieve this by implementing authentication, authorization, encryption, and input validation. It’s also important to ensure compliance with relevant regulations and standards by implementing appropriate security controls and auditing mechanisms. By prioritizing security throughout the development lifecycle and staying abreast of emerging threats, you can safeguard sensitive data and maintain the trust of your users. Remember that security vulnerabilities can expose your application to various risks, which can be costly in terms of reputation and financial losses. Therefore, always prioritize security in your application development process.

![Application Architecture](/assets/security-and-compliance.png)

## Conclusion

By incorporating these strategies and continuously monitoring and optimizing your system, you can design a high-load system capable of handling 100k — 1m RPS using Node.js. It’s important to conduct load testing and performance tuning regularly to ensure your system can handle the expected workload efficiently.

And lets try to combine all together:

![Application Architecture](/assets/highload-system.png)

Here is a high-level overview of the components that make up a high load system, with the hope that it is understandable. Please keep in mind that this is just an overview.

