DEV Community: Sabbir Ahmmed

Docker beginner approach A-Z that you should know! part 2 | End

Sabbir Ahmmed — Sun, 19 Dec 2021 04:37:02 +0000

Previously, I discussed in detail about Docker's theoretical part and installation process. Before starting this coding part, if you don't know about docker, please read part 1 first click here. And if you already know about docker's basic knowledge, you're welcome to part 2.

Linux

I told you that I will teach you basic Linux commands that are needed only for docker. And I hope, it will be very helpful to start not only docker but also to run the Linux operating system. Open your terminal and type

sudo su

sudo super user do and su lets you switch user so that you're actually logged in as a root user.
pwd -> Used to find out the path of the current working directory(folder) you’re in.
cd -> To navigate through the Linux files and directories, use the cd command.
ls -> If you want to see the list of files on your Linux system, use the ls or ls -a command.
mkdir -> Use the mkdir command when you need to create a folder or a directory.
rmdir -> Use rmdir to delete a directory. But rmdir can only be used to delete an empty directory. To delete a directory containing files, use rm.
rm -> Use the rm command to delete files and directories.
touch —> The touch command is used to create a file.
cat -> we can create and concatenate( join) files.
vi -> text editor, you can modify and save file.
echo —> The echo command helps us move some data, usually text into a file.
cp — Use the cp command to copy files through the command line. It takes two arguments: The first is the location of the file to be copied, the second is where to copy.
mv — Use the mv command to move files through the command line. We can also use the mv command to rename a file.
sudo apt-get update -> It is good to update your repository each time you try to install a new package.
sudo apt-get upgrade -> You can upgrade the system

Docker 💥💥💥

image to container 🇧🇩

First of all, we want to create a container and to create a container we need an OS image. So, we pull an image from the docker hub. Before starting, we need root access, open terminal and run

sudo su

Start your docker service and run

service docker start

you can see docker information using docker info
However, at this time our goal is to create a container. We need an OS image and we want to take the Ubuntu OS image. For that, run

docker images

now see that we have no image so we want to pull an image from the docker hub. For that, run

docker pull ubuntu

Now see the real magic. It first searches on our local environment. But we have no ubuntu OS image and that's why it pulls from the docker hub and looks at the file size, it is only almost 28 MB! I already said that docker OS images are light in weight. After downloading and extracting, the file size stands around 72 MB! Now again run

docker images

This time you found an OS image. Congratulations! 1st step done. You can try to pull centos OS using docker pull centos

I told you, we have 3 ways to create an image. And one of them is done, pulling images from the docker hub.🔥

It's time to make a brand new container. Remember that we have ubuntu OS image, so run

docker run -it --name ubuntu_container1 ubuntu /bin/bash

wow! it is looking like some weird things😨. Okay, let me explain. Here run is a combination of create and start. On the other hand, -it means interactive mode with a terminal. Then if we want to give a name for a container, we have to use --name command then the container's name. In our case, container name is ubuntu_container1. After that, we have selected an image and /bin/bash always fixed here. So,

docker run -it --name container_name image_name /bin/bash

Now, you're in your container. Run ls on your terminal. You will see Linux directories. And it is now your development environment as like your personal computer. You can create and run your application in the container.

Else, you maybe noticed that we get a container ID besides of root@ on the terminal.

Now, create a file in your container by using

touch container1.txt

to see this file run ls command. You see! You've created a file in your container. Not only files but also any applications that you want to create and share with others, you can!

To exit or stop your current container, use exit command.
And to see your all containers, run

docker ps -a

You see all containers here but at this time we can see only one container and which is our ubuntu_container1. Carefully observe, here we found container ID, IMAGE (we used ubuntu, remember?), NAME etc. But if we want to see just running container, we just run docker ps At this time, we have no running container. Because we exit our container.

container to image 🇧🇩

We have a container (ubuntu_container1), now we want to convert container into image. So that we can share our files or projects with others. Remember? in our container we created a file (container1.txt). And now we want to share it through an image. So run

docker commit ubuntu_container1 my_image1

Here, ubuntu_container1 is our container name that we want to convert into an image and my_image1 will be our new image name.

To see our new image, run

docker images

And boom 💥, do you see? In the image list, you see our my_image1 image file. Now you can create a container by using this image and you will find container1.txt file by running ls command that we created.

Again, to create a container by using this image, run

docker run -it --name ubuntu_container2 my_image1 /bin/bash

Now run ls you will find our container1.txt file 🤩.

Exit or stop your container by using exit command and run docker ps -a this time, you will find 2 containers, ubuntu_container2 is the recent one. And one was created by ubuntu image and the other was created by my_image1 image. Make sense?

Good to know
To enter an existing container, run

docker attach container_name

To delete a container

docker rm container_name/id

To delete an image

docker rmi image_id

To start an existing container but doesn't enter into the container

docker start container_name

To start an existing container

docker stop container_name

upload image into docker hub 🇧🇩

To share your docker image with others, you have to upload your image into the docker hub. For that, first you have to create an account on hub.docker.com. Simple sign-up process! After successfully sign-up, back your terminal and run

docker login

then enter your username and password and if all is okay, it will show you Login Succeeded. And now you're ready to upload your image into the docker hub.

We need to tag our image. That mean's, we have to set a name that we want to store in our docker repository. so run

docker tag my_image1 sabbir185/my_image1

after tag, our container image name and then a name that we want to set to store our container image. For example, I set a tag name sabbir185/my_image1 for our container image my_image1.

Now run the push command to upload the image. After push command, needs tagged image name. And my case sabbir185/my_image1. Now hit enter

docker push sabbir185/my_image1

Refresh your docker hub profile, you will see an image. 🥳😎

Now, you can pull your docker image or share it with others. For example in my case, my docker image sabbir185/my_image1

If I want to pull my docker image, I just run

docker pull sabbir185/my_image1

Remember? I have already discussed it 🤩🥰.
.

Dockerfile to image 🇧🇩

I told you, there are 3 ways to get an image. This is another method to gain a docker image and not only a popular one but also easy one of them. To create an image, first we have to create a Dockerfile, so run

touch Dockerfile

After that, open and write what you want to build. For my case, I want to create a ubuntu image and in image file, want to create a file name test1.txt. You have to open Dockerfile by

vi Dockerfile

And press i for write into the text editor.
FROM ubuntu
RUN echo "Welcome to docker" > /tmp/test1.txt

press Esc key and :wq then enter. Now run to build image

docker build -t image2 .

You can set any image name instead of image2

Check image

docker images

Bonus talk
There are some other topics. For example docker volume, port/expose, docker-compose etc. But For a beginner, I think it's enough for you now. Practice it and then explore some advanced topics that you want.
.

`Thanks for your time`🥰

Docker beginner approach A-Z that you should know! part 1

Sabbir Ahmmed — Thu, 16 Dec 2021 06:56:38 +0000

Docker is one of the hottest topics in the software technology industry. It was first introduced in March 2013 and developed by Kamel Founadi, Solomon Hykes, and Sebastien Pahl. Docker is written by Go programming language. Here, I will try my best to introduce docker's main concepts to you very easily. First of all, you have to know about Linux. If you already know about Linux's basic commands so you're welcome. We can install docker on any OS but docker-engine runs natively on Linux distribution.

But don't worry I will teach you Linux's basic commands.🤩

So, what is docker?
Docker is an open-source centralized platform designed to create, deploy and run applications. Docker is a set of platform as a service ( PaaS ) that uses OS level virtualization. Do you understand? 😄

Okay have a look, by using docker we can share our applications or projects very easily with others. Sometimes our development environment and other people or team's environments are different. So that, they can't run your project as you can from your local environment. Because maybe other environments have missed some dependencies that are required to run your application. This is a very panicked situation. And to resolve this situation Docker has come. Docker builds a container with necessary dependencies. Each container treats as our local machine.

Docker's concept
Docker's main concept comes from Virtual Machine. Docker is a tool that performs OS ( operating System ) level virtualization, also known as containerization. And every docker's VM is called a container. Docker's concept is different from actual VM ( virtual machine ). VM uses hardware-level virtualization.

OS level virtualization: A virtual machine concept that uses mainly operating systems. It has no direct relation to the host ( hardware resources for example RAM, processor, hard disk, etc ). When it's needed, that time only uses host resources. It does not block host resources. It's no need for brand new operating system installation panic because it adopts the main OS as needed. That's why Docker container is very lightweight.

hardware-level virtualization: Virtual Machine ( like VMware ) blocks defined host resources that's why we can able to create a limited number of VM on our machine. It has a direct relationship with host resources. Else, every VM needs to install individual a brand new OS and other necessary applications to run our projects or applications. It is a very time-consuming task. For these panic reasons, docker has come into the picture.🥳💥

Components of docker:
Docker container: A container is just like a Virtual Machine. it holds the entire packages that are needed to run the application. A container also holds OS but this OS is very lightweight. Some people say that container has no OS but practically container holds OS. It adopts necessary files from the docker daemon and base OS. First of all, the docker daemon search files locally but if not found, it pulls files from the docker hub.

Docker engine: Docker engine is called the docker daemon. Docker daemon runs on the host OS. It is responsible for running docker containers and managing docker services. Docker daemon holds all images to create a container.

docker image: Docker images are the read-only binary templates used to create docker containers. An image holds all packages. To create a container, an image is needed. We can get an image in 3 ways:-

By taking an image from the docker hub.
By creating an image from Dockerfile.
By creating an image from exiting docker container.

Docker client: Docker users can interact with docker daemon through a client. Docker client uses CLI (Command line interface) and Rest API (Application Programming Interface) to communicate with docker daemon. When a user runs any command on the docker client terminal, the docker client terminal sends it to the docker daemon.

Docker host: Docker host is used to provide an environment to execute and run applications. It contains the docker daemon, images, containers, networks and storage. Host means our hardware section.

So, why should we learn docker?
I have already discussed actually docker's necessity. So, in a short form --

To solve our application's dependencies problem
It doesn't pre-allocate RAM.
CI ( continuous Integration ) efficiency.
less cost ( hardware/resources are used as needed )
It is light in weight.
It can run on physical h/w or virtual machine or even on the cloud.
You can re-use the image.
It takes very less time to create a container.
Easy to create, deploy and run application.
Docker container holds your all software development packages and after making a docker image, you can share it with everyone🔥

Enough talks, let's code 😍
To work with docker we need to install docker in our system. Download or use command lines from this click here to install docker and follow instructions as said there. Very easy process, doesn't it? 😎

After successfully install open your terminal or cmd(windows user)

docker --version

It will show a version number. Congratulations!🥳 docker installation has been successfully done.

If it doesn't work, don't worry. You have to turn on docker's service. Open your terminal and type

service docker start

After check status

service docker status

docker --version

Now you're ready to go into docker's world✌️😁

`Next part 2` click here

'this' keyword in JavaScript simple explanation with call(), apply(), bind()

Sabbir Ahmmed — Sat, 31 Jul 2021 12:22:23 +0000

'this'

First write a simple code on your browser console ,
console.log(this);
wow! You see a window object, right ?! but why?

For discussion, I divided this topic into 4 parts --

Implicit binding
Explicit binding
new binding
window binding

Implicit binding :

const student = {
    name: 'Sabbir',
    dept: "CSE",
    namePrint: function(){
        console.log(`My name is ${this.name} Ahmmed`);
    }
}

student.namePrint();

from above code we can see that, we are printing name from object using ‘this’ keyword. ‘this’ actually reference a nearest object and that’s why here nearest object is student and inner this object namePrint is a property which is a function and print name of student. So, here ‘this’ holds properties of student

Another,

const student = {
    name: 'Sabbir',
    dept: "CSE",
    namePrint: function(){
        console.log(`My name is ${this.name} Ahmmed`);
    },
    student2: {
        name: 'Jubayer',
        dept: "EEE",
        deptPrint: function(){
            console.log(`Department name is ${this.dept}`);
        }
    }
}

student.namePrint();
student.student2.deptPrint();

here, student2 is a property of student but student2 itself is an object. So, we know that ‘this’ holds nearest object. That’s why here ‘this.dept’ prints EEE not CSE.

Simple and bonus Tricks : look at your calling function deptPrint(), this function is calling using dot(.), before dot(.) you see an object ( student2 ) right ? Yes, for deptPrint function ‘this’ holds student2 properties ! nearest properties !

So, can you tell me which object actually reference for namePrint()’s ‘this’ ? comment please

Explicit binding : Call(), apply(), bind()

call() : call method is helper function of this. 'this' keyword by default reference a nearest object. But using call() method we can set that which object we can call for a function. call() can take parameter and 1st is an object and 2nd multiple parameter for function .
For example : functionName.call(objectName, p1, p2, .... );

var printName = function(v1, v2, v3){
    console.log(`${this.name} is ${v1}, ${v2} & ${v3}`);
}

var sabbir = {
    name: "Sabbir",
    dept: "CSE"
};

var v1 = 'good';
var v2 = 'boy';
var v3 = 'in the class';

printName.call(sabbir, v1, v2, v3);

apply(): Same as call() but call() can take parameter individually, On the other hand apply() can take array as a parameter. For example :
const p = [p1, p2, p3,...]
functionName.apply(objectName, p );

var v1 = 'good';
var v2 = 'boy';
var v3 = 'in the class';
const v = [v1, v2, v3]

printName.apply(sabbir, v);

bind(): Same as call() but doesn't call immediately. It stores values in a variable. After that, we have to call that variable as a function. For example :
const newFunc = printName.bind(sabbir, v1, v2, v3);
newFunc();

var printName = function(v1, v2, v3){
    console.log(`${this.name} is ${v1}, ${v2} & ${v3}`);
}

var sabbir = {
    name: "Sabbir",
    dept: "CSE"
};

var v1 = 'good';
var v2 = 'boy';
var v3 = 'in the class';

const newFunc = printName.bind(sabbir, v1, v2, v3);
newFunc();

new binding :

function Student(name, dept){
    // let this = Object.create(null);

    this.name = name;
    this.dept = dept;
    console.log(`${this.name} is now ${this.dept} student.`);

    // return this
}

const sabbir = new Student('Sabbir', 'CSE');

'new' keyword creates an object and ‘this’ keyword just reference that object’s properties. So, ‘this’ actually holds new Student’s properties.

window binding:

At the beginning , we print ‘this’ keyword that we found a window object. Because, I already told you that ‘this’ actually points to the nearest object, right? so, when ‘this’ does not find any of our custom-defined objects, it points to window object for browser and global object for Nodejs. Because we know that by default every browser has a window object.

Bonus Tricks :

If you confuse about the reference of ‘this’, just do console.log(this) and find out its object.
You may use “use strict” to the beginning of a script or a function.

JavaScript tricky interview questions

Sabbir Ahmmed — Fri, 21 May 2021 15:37:29 +0000

What are the truthy and falsy values of javascript?

JavaScript falsy means false of boolean condition context. Mainly, six expressions are called falsy. They are false, ‘’(empty string), undefined, null, NaN and 0. And the rest of the expression treats truthy. For example –

let value = NaN;

if(value) {
    console.log( “Truthy value”);
} else {
    console.log( “Falsy value” );
}

Output: False value, because here boolean condition expression is false.

What is the difference between null and undefined?

null and undefined both are reserve keywords of javascript. In javascript null is used to assign an empty value, that’s means nothing. On the other hand, if we declare a variable but not define it yet at that time, the variable will show undefined. For example –

let value;
console.log( value );     // undefined

Else, if we don’t return anything from the function, it will show undefined.

What is the difference between == and === ?

Double equal ( == ) is used for comparing two variables, but it doesn't check their data types. If one is an integer and another is a string but both contain the same value then it will be true. For example — -

let x = 4 ;
let y = “4” ;
if ( x == y ) {
    console.log( “ condition is true “ );
}

But, three equal not only compare two variables but also check their data types. If data types are the same both, so they are truthy.

Define scope and block scope

The scope is just like the area. One is global scope and another is local scope. In general, when we declare a variable following by ES6 rules such as let and const in the function that variable is called function scoped variable or local variable. But if we want to declare a variable outside of a function is called global variable and its access is everywhere. For example –

const x = 15       // this is global variable or global scope

function doSomething() {
    const y = 15 ;           // local or function scoped variable
    const sum = x + y ;     // the variable which are inside of 
    return sum;            // curly braces are called block scope variable
}

console.log( doSomething() ); // 30

Noted that, you can’t access y and sum variables outside of doSomething() function. The scope of y and sum are only in doSomething().

let and const are called block scope keywords. You can’t access outside of block curly braces { }. And var is a keyword that is called function scope variable.

What is hoisting?

Hoisting in a JavaScript's default behaviour. In javascript, var is a keyword that is used to declare variables. This var allows hoisting, hoisting means you can access a variable from anywhere in the parent scope. Hoisting set a reference of variable in the global scope or immediate parent scope. But doesn’t carry assigned value. For example –

const playFootball = () => {

    console.log("gameName hoisting : ", gameName );     // undefined

    let rain = true;

    var gameName = "Football";

    console.log("status hoisting : ", status );       // undefined

    if( rain ) {
        var status = "continue game" ;
    }

    console.log("status : ", status );               // continue game

}

playFootball();

NB : const, let and arrow function do not support hoisting

What is Closure in JS?

The closure is a hot topic of JS. I’m going to discuss this here briefly. In JavaScript, closures are created when the inner function is created inside of a function. That inner function holds the reference from its parent function scope. For example –

Here, num2 is used by the inner function that time closure appears. And num1 comes from global scope, global variables are always reserved and any function can use them. But a variable in the function when it is used by an inner function that time closure is created.

A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function’s scope from an inner function.