Skip to main content


Showing posts from 2022

Shikaku Talks To Shikamaru

It was after Asuma lost the battle with Akatsuki.

Phases of Node.js Event Loop

We know that a Node.js application is run in a single-threaded fashion. But, it can handle multiple asynchronous operations in the background and exhibits features as if it is a multi-threaded application. At the base level, Node.js is built on C++ which actually allows the existence of multiple threads. While that's not the actual basis, Node.js utilizes the  libuv library that allows it to interact with the operating system and utilize available resources efficiently. The library enables asynchronous I/O operations such as file reading, database querying, data transferring over the network, and so on, then it will trigger the registered callback for each completed I/O operation to run. Node.js manage all the callbacks in a mechanism called " event loop ". An event loop is a loop of sequential processes which are grouped into several phases. It handles callbacks of asynchronous I/O operations and asynchronous calls initiated by objects or functions in the main appl

Configure Gitlab SMTP Setting

Gitlab CE or EE is shipped with the capability to send messages through SMTP service as the basic feature to send notifications or updates to the users. The configuration parameters are available in /etc/gitlab/gitlab.rb . Each SMTP service provider has a different configuration, therefore the Gitlab configuration parameters should be adjusted according to the requirements. Some examples have been provided by Gitlab here . This is an example if you use the Zoho service. gitlab_rails['smtp_enable'] = true gitlab_rails['smtp_address'] = "" gitlab_rails['smtp_port'] = 587 gitlab_rails['smtp_authentication'] = "plain" gitlab_rails['smtp_enable_starttls_auto'] = true gitlab_rails['smtp_user_name'] = "" gitlab_rails['smtp_password'] = "mypassword" gitlab_rails['smtp_domain'] = "" This is another example of using Amazon SES w

Measuring Correlation

If we want to know a correlation between a boxer winning a match and using red pants, we can mathematically determine it based on past records of those conditions. There are four possible combinations of the conditions. The boxer loses and he doesn’t use red pants (00) The boxer loses and he uses red pants (01) The boxer wins and he doesn’t use red pants (10) The boxer wins and he uses red pants (11) For example, we have the following past records. Condition “00” is 23 times Condition “01” is 10 times Condition “10” is 45 times Condition “11” is 9 times Then, we can use the phi coefficient formula. The result of this formula is between -1 and 1. If the result is close to 0, it means the conditions have no correlation. If it is close to 1, it means the conditions are strongly correlated. Meanwhile, if it is negative, the correlation is strong but in the opposite way. The formula is as follows. phi = (n11 x n00) – (n01 x n10) / sqrt(n1X x n0X x nX1 x nX0) n1X represents the condition wh

Elements of UI Design

There are some essential elements in designing a user interface. I found that the following items are necessary to bring up a certain feeling, thought, or perspective for the user of our product. Color Color can shape a mood for the user. Combining multiple colors should be carefully picked to create a comfortable look. One of the tools available online to pick colors is here . Positive and Negative Space Positive space is the element containing the main content or information. Meanwhile, negative space is the distance between main elements or empty space around them. Each main element should have distance or space from each other to nicely navigate the focus of the users from one information to another. Typography Typography includes selecting appropriate fonts with good looks and aligning text content on the page. Microcontent We need to provide some short texts or content on a page to make it easy for the user to skim the information on th

First Appearance of Titan Eren

 When Mikasa was trying to grasp herself, a titan appeared killing the other titans.

Downloading A Large File From Google Drive

I just found a helpful answer from Quora about downloading a large file from Google Drive. It utilizes Google Drive API for downloading the file. The steps are as follows. Get the file ID from the shareable link URL. For example, the URL has a format similar to this: , then the file ID is THE_FILE_ID . Go to Google OAuth 2.0 Playground . On this page, we can get an access token for utilizing Google API to download our file. Select the Drive API v3 and authorize it. Then, keep the access token that is available on the "Exchange authorization code for tokens" tab. Last, we can utilize curl to download the file using a terminal. curl -H "Authorization: Bearer THE_ACCESS_TOKEN" -o THE_OUTPUT_FILE.ext

Utilizing Docker Secret

It likely happens that we need to provide some secrets like passwords, keys, or private things into our Docker containers. If we use the docker-compose tool to generate our containers, we basically can put the secrets as environment variables in the docker-compose.yaml file. But, what if we want to share our configuration with the others, they will find those secrets too. So, for overcoming that issue, we can utilize a feature provided by Docker itself which is the Docker secret, or we can just call it secret . For instance, we want to build a container for the PostgreSQL database. The PostgreSQL image allows us to set a custom database password by providing a value for the POSTGRES_PASSWORD or POSTGRES_PASSWORD_FILE variable. services: postgres: image: postgres environment: - POSTGRES_PASSWORD=$3cureP4ssword Or, we can utilize the Docker bind-mounting to store a file and instruct the Docker to read the secret information from the mounted file. services:

Principles of UX Design

If we want to elaborate a user experience (UX) design for our product, we need to understand some principles of a good UX design. Our design should be based on specific reasons and have certain intentions for our users and ourselves as product owners or as a business. These are several principles that should become our consideration in generating the design. Usefulness We build a product with a desire for providing solutions for any specific needs of the users. So, it is important to make sure that any design elements are provided to make the users completely gain the benefit of using our product and solve their problems. Usability Visions and our good intentions are not enough to build a great product if we don't provide clear ways for the users to take the most benefit of the product. Usability is a focus to provide easiness for the users in utilizing our product. Desirability Why are some products or services instantly abandoned by their users

When Mikasa Got So Emotional But Had To Fight

 She just tried to suppress her feeling.

Generate API Documentation Using Swagger Module in NestJS

Swagger provides us a standard to generate API documentation based on the Open API specification. If we use NestJS for building our API providers, we can utilize a tool provided by NestJS in the  @nestjs/swagger  module to generate the documentation automatically in the built time. This module also requires the swagger-ui-express module if we use Express as the NestJS base HTTP handler. Set Swagger configuration First, we need to define Swagger options and instantiate the documentation provider on the main.ts file. import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger'; // sample application instance const app = await NestFactory.create(AppModule); // setup Swagger options const options = new DocumentBuilder() .setTitle('Coffee') .setVersion('1.0') .setDescription('Learn NestJS with coffee') .build(); // build the document const document = SwaggerModule.createDocument(app, options); // provide an endpoint

Building Reducer Using Redux Toolkit

Redux Toolkit is one of the libraries that can help us manage our application state which depends on Redux. It allows us to create reducers within our application and separate each reducer from one another based on any criteria that we desired in a specific kind of module. There are some approaches that we can utilize to build reducers in Redux Toolkit. Basic Shape const slice = createSlice({ // ... reducers: { increment: (state) => { state += 1; } } }); On the code above, it seems that we mutate the state, but actually, Redux Toolkit utilizes Immer in the backstage so it will be translated into immutable operation. Then, unlike legacy libraries that require us to manually define the action that will be dispatched to be handled by a specific reducer, Redux Toolkit can generate action creators for us. const { increment } = slice.actions; // "increment" is the action creator Then, we can dispatch the action inside our compone

Double Invoking In React Application with Strict Mode Enabled

When we use create-react-app to generate our application source code, we will be provided with a base code that enables  React.StrictMode by default. This wrapper component doesn't render an HTML element but it performs useful functionality to verify that our application is safe for production. It checks for legacy or deprecated React functions or APIs, unexpected side-effects, and unsafe lifecycle. We can read the details about those functionalities on its documentation page . To help us spot side-effects, React will double-invoking several functions in our application such as render , constructor , functions passed in useMemo or useReducer , and so on. By double-invoking such functions, we can detect if unexpected results will show up. But, this process will be initiated only in development mode. When we ship our application in a production environment with Strict Mode enabled, double-invoking will never happen. This is why when we render a component that contains useEffect

Tokyo - Yui


Limiting Bitrate and Network Throttling

We may limit incoming or outcoming data rates to/from our infrastructure to maintain the stability of our service for customers. Bitrate limitation is an action to limit the number of bits that can be passed through a transmission channel in a period of time. Network throttling is an intentional action to slow down transmission speed in a network channel. It is not only about limiting bitrate but also limiting the allowed number of requests in a period of time. There are several tools and techniques that can be used to apply bitrate limitation and network throttling. Wondershaper It is an easy-to-use tool for Linux and is already in the package repository. It can limit the bit rate that can be achieved by network interfaces in the system. We can install it by running the following command. apt install wondershaper We can choose an interface to have a limitation either or both on download and upload. wondershaper <interface-name> <download-rate-in-bps> <upload-

Handle File Upload with Express and Multer

Express undoubtedly has become a popular framework for building web applications based on Node.js. It is shipped with support for handling file uploading using middleware that takes the user requests, parses the contents for the files, and provides the next handler with the files information. The following snippet shows a basic example of handling files uploading in Express using Multer. const multer = require('multer'); const storage = multer.diskStorage({ destination: (req, file, cb) => { // store files to "uploads/" directory cb(null, 'uploads/'); }, }); const upload = multer({ storage }); // initiate an upload handler that can accept multiple fields and multiple files const uploadHandler = upload.fields([ { name: 'galleryImages', maxCount: 10 }, { name: 'userFiles', maxCount: 2 }, ]);'/upload', uploadHandler, (req, res) => { res.json(req.files); }); The sample above can be used if we just

Object Storage Comparison of DigitalOcean, Linode, and UpCloud

In this post, I want to show a test result of object storage services provided by DigitalOcean, Linode, and UpCloud. The result shows the average durations required to download/upload files from/to their cloud infrastructures. But, before we go into the test detail, let us overview the user features provided by each cloud provider. DigitalOcean has the most advanced features compared to the rest. By utilizing its user dashboard, we can set a custom domain for the CDN of object storage, customize permission per object, and custom CORS headers. UpCloud has a more straightforward interface but with a unique concept for creating separate bucket domains (directories) in a single object storage subscription. Linode has the simplest features in its interface but it provides CLI tools for managing the buckets and stored objects. Now, let us go back to the main topic. For the test, I deploy an AWS EC2 server based in Tokyo as a tester node. Then, I set separate object storages on DigitalOcean,

Zoro vs Mihawk

An old fight and the first encounter with Mihawk. " Scars on the back are the swordman's shame "

Managing MongoDB Records Using NestJS and Mongoose

NestJS is a framework for developing Node.js-based applications. It provides an additional abstraction layer on top of Express or other HTTP handlers and gives developers a stable foundation to build applications with structured procedures. Meanwhile, Mongoose is a schema modeling helper based on Node.js for MongoDB. There are several main steps to be performed for allowing our program to handle MongoDB records. First, we need to add the dependencies which are @nestjs/mongoose , mongoose , and @types/mongoose . Then, we need to define the connection configuration on the application module decorator. import { MongooseModule } from '@nestjs/mongoose'; @Module({ imports: [ MongooseModule.forRoot('mongodb://localhost:27017/mydb'), ], controllers: [AppController], providers: [AppService], }) Next, we create the schema definition using helpers provided by NestJS and Mongoose. The following snippet is an example with a declaration of index setting and an o

Backup and Restore PostgreSQL Database

PostgreSQL has been shipped with a lot of tools for ease of managing the database. Some actions that we typically perform in managing databases are backing up a database and restoring it to another database server. In PostgreSQL, we can utilize pg_dump to back up the data from a database and psql or pg_restore to restore the data into a new database. Generating A Backup File There are several available formats for the exported data: plain, directory, compressed, and custom. The plain format is using plain SQL syntax to export the data. To make the tables are exported separately, we can utilize directory format. The custom format is utilizing a built-in compression mechanism and results in an optimized binary formatted file. It is suitable for a large database. If we use a custom format, we can only restore it using pg_restore , but we have the ability to selectively choose desired tables to be restored. The following command is used to generate a plain formatted file with th

Resize VirtualBox LVM Storage

VirtualBox is a free solution to host virtual machines on your computer. It provides configuration options for many components on our machine such as memory, storage, networking, etc. It also allows us to resize our machine storage after its operating system is installed. LVM is a volume manager in a Linux platform that helps us to allocate partitions in the system and configure the storage size that will be utilized for a specific volume group. There are some points to be noticed when we work with LVM on VirtualBox to resize our storage. These are some steps that need to be performed. 1. Stop your machine before resizing the storage. 2. Set new storage size using GUI by selecting " File > Virtual Media Manager > Properties " then find the desired virtual hard disk name that will be resized. OR , by running a CLI program located in " Program Files\Oracle\VirtualBox\VBoxManage.exe ".  cd "/c/Program Files/Oracle/VirtualBox" ./VBoxManage.exe list

Best Action & Thriller Movies

Here are some latest action and thriller movies that I think very recommended to watch.  Nobody (2021) A guy who seems like a special agent veteran has to back to his old job that is getting rid of some bandits. In the beginning, we see an ordinary man who runs his boring routines with his family. Until a couple of robbers broke into his house to take some worth in it but accidentally stole his daughter's kitty bracelet. Yeah, just because of the cheap bracelet and getting trouble with drunk guys on the way back home, he has to face bigger trouble. This movie is written by one of John Wick's writers, maybe that's why the main guy seems to be so badass. Don't Breathe 1 (2016) & 2 (2021) A war veteran who is blind and lives alone is forced to be a horrific man. Some intruders who broke into his house, make everything change. In 2016, the intruders want his treasure but end up finding something creepy in the basement. In 2021, he has to fight some bad guys who want to

Redirect A Domain or Sub-domain To Another Domain in Amazon Route 53

Amazon Route 53 is used for registering domains and storing DNS records. Basically, it cannot handle HTTP requests redirection which is commonly handled by web or proxy servers.  So, we need to implement a kind of web server in front of our service to make redirection. There are two methods that we can try to achieve our need for redirection. First, we can utilize Nginx (or other tools) as a proxy to our service with an additional configuration block for redirection. Second, if our service is hosted on Amazon EC2, we can activate the load balancer service and add a listener for redirecting specific requests. Nginx as Proxy Server The configuration for redirection is generally as follows. server { listen 80; server_name; return 301$request_uri; } EC2 Load Balancer This method utilizes the load balancer feature in Amazon EC2. In the load balancer listener setting, we need to add a rule to redirect a specific request based on the

Oh No, My Gitlab Instance Got Hacked

I manage a self-hosted Gitlab instance on a server in DigitalOcean. A few months ago, I got a notification from DigitalOcean Security Center that my instance has been disconnected from the network because it was detected performing a kind of Distributed Denial of Service (DDoS) attack. I tried to solve the issue, I suspected that it was just a Gitlab runner process that made some requests that were falsy detected as a DDOS attack. DigitalOcean has very strict rules for this case that it becomes difficult for me to re-activate the network connection of my server before I perform a kind of recovery process and system scanning. That's why I choose to deploy a new server and back up the repository. After I managed to deploy a new instance and re-run the repository server, I upgraded the server with the latest patch that is suitable. I also thought that the issue was only caused by falsy security detection. After that moment, I left my server untouched for months lat

Modifying Video Data using FFMPEG

FFMPEG has become very popular for so long time as a tool that can help us manipulate, convert, or configure video and audio data. We can resize our video, convert a file into a different container, change the bitrate, embed subtitles, or even stream real-time video. These are a few examples of its utilization. Converting file into a different container For example, we want to convert an MKV file into MP4 without changing its codec. ffmpeg -i input.mkv -codec copy output.mp4 Or, we want to convert an MP4 file into Webm with some customizations. ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 28 -b:v 0 -b:a 128k -c:a libopus output.webm Change video size We can resize a video width and height too. ffmpeg -i input.mp4 -vf scale=1280:720 output.mp4 We can set the width or height to "-1" to keep the origin ratio. Note that some codecs require a size that can be divided by 2 to be successful. ffmpeg -i input.mp4 -vf scale=1280:-1 output.mp4 Insert subtitles We can attac

Utilizing Decorators in Typescript

Decorator is a quite good feature in Typescript even though it is currently still in an experimental state. But, because of its advantages, it is commonly used by any developer. Such a framework like Angular also heavily uses this feature from the beginning. A decorator is a syntax for calling a function on the thing that it is decorated . It acts like a wrapper function or higher-order function that results in an improved thing or thing with additional things. The thing may be a class , class method , class property , or method property . The thing that will be decorated must have a specific type signature . A class decorator can only decorate a class, an object that has a constructor. @mydecorator class MyClass {} The code above is similar to the following code. class MyClass {} const WrappedClass = mydecorator(MyClass); We will take the example of utilizing a class decorator. First, we need to create a type of class constructor that passes a generic type for defining the

Fibonacci In Javascript Using Generator Function and Iterable

Generating the Fibonacci sequence is usually demonstrated in computer science courses to show an implementation of a recursive function. Besides the recursive function, we can utilize the generator function in Javascript for generating the sequence. Let us take a look at a few methods that we can perform. For instance, we will create some functions to get the value of a certain position in the Fibonacci sequence. Then, we will measure up the performance to get solid ground on what we should choose in our application. Recursive Function This is the simplest method for getting the value in the sequence. We use 1, not 0, as starting position to make this function more human. function getFibonacci1(pos) { if (pos === 1) { return 0; } if (pos === 2) { return 1; } return getFibonacci1(pos - 1) + getFibonacci1(pos - 2); } Generator Function In this method, we create a generator function for generating sequence and the actual function for providing the result. The