Beginners Guide To Docker
Tags: webdev, docker, devops, programming
Published: 2023-09-28 08:49:58

Welcome to my blog on "Beginners Guide To Docker"! In today's fast-paced world, where technology is advancing at an unprecedented rate, it is essential to keep up with the latest trends and tools. Docker is one such tool that has gained immense popularity in recent years. Docker is an open-source platform that allows developers to build, ship, and run applications in containers. It provides a simple and efficient way to package and deploy applications, making it easier to manage and scale them. In this blog, we will cover all the basics of Docker, including what it is, how it works, and how to get started with it. Whether you are a beginner or an experienced developer, this blog will provide you with a comprehensive understanding of Docker and its benefits. So, let's dive in and explore the world of Docker and let's understand, what are containers, volumes, images and everything single thing about Docker.


## Docker

Docker is an open-source platform that allows developers to build, ship, and run applications in containers. Containers are lightweight, portable, and self-contained environments that can run anywhere, from a developer's laptop to a production server. Docker provides a simple and efficient way to package and deploy applications, making it easier to manage and scale them. With Docker, developers can create a container image that contains all the dependencies and libraries required to run their applications. This image can then be shared with others, making it easy to collaborate and deploy applications across different environments.

Docker is based on the concept of containerization, which is a method of virtualization that allows multiple applications to run on the same operating system without interfering with each other. Each container is isolated from the host system and other containers, providing a secure and predictable environment for running applications. Docker uses a client-server architecture, where the Docker client communicates with the Docker daemon to build, run, and manage containers. The Docker daemon runs on the host system and manages the containers, including their creation, deletion, and resource allocation.

One of the key benefits of Docker is its portability. Containers can be easily moved between different environments, such as development, testing, and production, without any changes to the application code. This makes it easier to deploy applications and reduces the risk of errors caused by differences between environments. Docker also provides a consistent environment for running applications, which helps to reduce the time and effort required for testing and debugging. Overall, Docker is a powerful tool that can help developers to streamline their development and deployment processes, making it easier to build and deliver high-quality applications.


## The Docker architecture

The Docker architecture consists of three main components: Docker Engine, Docker Hub or Registry, and Docker CLI.

Docker Engine is the core component of Docker that runs on the host machine and manages the containers. It is responsible for creating, starting, stopping, and deleting containers, as well as managing their resources, such as CPU, memory, and storage. Docker Engine also provides a runtime environment for containers, allowing them to run on the host machine without interfering with other containers or the host system. Docker Engine is available for different operating systems, including Linux, Windows, and macOS. Install Docker Engine from here

Docker Hub or Registry is a cloud-based repository where developers can store and share Docker images. Docker images are the building blocks of containers, containing all the dependencies and libraries required to run an application. Docker Hub provides a centralized location for storing and sharing Docker images, making it easy for developers to collaborate and deploy applications across different environments. Docker Hub also provides a range of tools and services, such as automated builds and image scanning, to help developers manage their images and ensure their security. Docker Hub

Docker CLI is a command-line interface that allows developers to interact with Docker and manage containers, images, and networks. It provides a set of commands that can be used to create, start, stop, and delete containers, as well as manage their resources and networks. Docker CLI also allows developers to build and push Docker images to Docker Hub, as well as pull images from Docker Hub and other registries.

Overall, the Docker architecture provides a powerful and flexible platform for building, shipping, and running applications in containers. By separating applications from their underlying infrastructure, Docker allows developers to focus on writing code and delivering value to their users, while also providing a consistent and secure environment for running applications.


## Difference between Docker and Virtual Machine

Docker and virtual machines (VMs) are both technologies used for deploying and running applications, but they differ in several key ways.

**Architecture**: Docker is based on containerization, while VMs are based on virtualization. Containers are lightweight and share the host operating system kernel, while VMs are heavier and require a separate guest operating system.

**Resource usage**: Docker containers use fewer resources than VMs because they share the host operating system kernel. This means that Docker can run more containers on a single host than VMs can run on virtual machines.

**Startup time**: Docker containers start up much faster than VMs because they don't need to boot a separate operating system. This makes Docker a better choice for applications that need to scale quickly or respond to changes in demand.

**Isolation**: Docker containers provide process-level isolation, while VMs provide full system isolation. This means that if one container fails, it won't affect other containers running on the same host. However, if a VM fails, it can affect other VMs running on the same host.

**Portability**: Docker containers are more portable than VMs because they can run on any host that supports Docker. VMs, on the other hand, require a hypervisor to run, which can limit their portability.

**Maintenance**: Docker containers are easier to maintain than VMs because they are smaller and have fewer moving parts. This means that updates and patches can be applied more quickly and with less disruption to running applications.

In short, Docker and VMs have different strengths and weaknesses, and the choice between them depends on the specific needs of the application being deployed. Docker is a good choice for applications that need to scale quickly, while VMs are better suited for applications that require full system isolation.

## Docker Container
Docker container is a lightweight, standalone, and executable package that contains everything needed to run an application, including code, libraries, dependencies, and system tools. It is a virtualization technology that allows developers to create, deploy, and run applications in a consistent and reproducible environment across different platforms and operating systems. Docker containers are based on the concept of containerization, which isolates an application and its dependencies from the underlying infrastructure, making it easier to manage and scale.

Docker containers are built using Docker images, which are essentially snapshots of a container's file system and configuration. Docker images are created using a Dockerfile, which is a script that specifies the application's dependencies, environment variables, and other configuration settings. Once an image is created, it can be used to create multiple containers, each running an instance of the application.

One of the key benefits of Docker containers is their portability. Because containers are self-contained and isolated from the underlying infrastructure, they can be easily moved between different environments, such as development, testing, and production. This makes it easier to deploy applications across different platforms and operating systems, without having to worry about compatibility issues.

Another benefit of Docker containers is their scalability. Because containers are lightweight and can be easily replicated, it is possible to quickly spin up multiple instances of an application to handle increased traffic or demand. This makes it easier to scale applications up or down as needed, without having to provision additional hardware or infrastructure.

Overall, Docker containers have revolutionized the way applications are developed, deployed, and managed. They provide a consistent and reproducible environment for running applications, making it easier to manage dependencies, scale applications, and deploy them across different platforms and operating systems. With the growing popularity of containerization, Docker containers are likely to become an increasingly important part of the software development and deployment landscape in the years to come.

## Docker Images
Docker images are a fundamental component of the Docker platform, which is a popular containerization technology used to package and deploy applications. A Docker image is essentially a lightweight, standalone, and executable package that contains everything needed to run an application, including the code, runtime, system tools, libraries, and settings. Docker images are created using a Dockerfile, which is a script that specifies the instructions for building the image.

Docker images are designed to be portable and can be easily shared and distributed across different environments, such as development, testing, and production. They are also immutable, meaning that once an image is created, it cannot be modified. Instead, any changes to the application or its dependencies are made by creating a new image based on the existing one. This makes it easy to maintain consistency and reproducibility across different environments and ensures that the application runs the same way every time it is deployed.

Docker images are stored in a registry, which is a centralized repository for storing and sharing images. The most popular registry is Docker Hub, which is a public registry that hosts millions of images. However, organizations can also set up their own private registries to store and manage their own images.

One of the key benefits of using Docker images is that they enable developers to easily package and deploy applications without worrying about the underlying infrastructure. This makes it easier to build and test applications, as well as deploy them to production environments. Docker images also help to reduce the risk of dependency conflicts and ensure that applications run consistently across different environments.

In summary, Docker images are a powerful tool for packaging and deploying applications. They are portable, immutable, and can be easily shared and distributed across different environments. By using Docker images, developers can focus on building and testing applications, while Docker takes care of the underlying infrastructure.

## Docker Volumes
Docker volumes are an essential feature of the Docker platform that allows for the persistent storage of data and files within Docker containers. A Docker volume is essentially a directory that is stored outside of the container's file system but can be accessed by the container as if it were a local directory. This means that data stored in a Docker volume will persist even if the container is deleted or recreated.

One of the primary benefits of using Docker volumes is that they allow for easy data sharing between containers. Multiple containers can be configured to use the same volume, allowing them to share data and files without the need for complex networking configurations. This can be particularly useful in microservices architectures, where different services may need to access the same data.

Docker volumes also provide a way to separate data storage concerns from the container itself. By storing data in a separate volume, it becomes easier to manage and backup data independently of the container. This can be particularly important in production environments, where data integrity and availability are critical.

There are several types of Docker volumes available, including host-mounted volumes, named volumes, and anonymous volumes. Host-mounted volumes allow a container to access a directory on the host system, while Named Volumes provide a way to create and manage volumes independently of the container. Anonymous Volumes are created by Docker automatically and are typically used for temporary data storage.

Overall, Docker volumes are a powerful feature that enables flexible and scalable data storage within Docker containers. By using volumes, developers can easily manage and share data between containers, while also ensuring data integrity and availability in production environments.


## Understanding the Difference Between Containers, Images and Volumes
A Docker container is a running instance of a Docker image. It is a lightweight and standalone executable package that includes everything needed to run an application, such as code, libraries, and system tools. Containers are isolated from each other and from the host system, which means that they can run multiple applications on the same host without interfering with each other.

For example, let's say you have a web application that requires a specific version of Python and a specific set of libraries. You can create a Docker container that includes the required Python version and libraries, and then run the application in that container. This way, you can ensure that the application runs consistently across different environments, without worrying about dependencies or conflicts.

Docker images are the building blocks of Docker containers. They are read-only templates that contain the instructions for creating a Docker container. Images are created using a Dockerfile, which is a text file that specifies the application's dependencies, environment variables, and other configuration details.

For example, let's say you want to create a Docker image for a web application that uses Node.js. You would create a Dockerfile that specifies the Node.js version, installs any required dependencies, and sets the environment variables. Once the Dockerfile is created, you can use it to build a Docker image, which can then be used to create Docker containers.

Docker volumes are a way to store and share data between Docker containers and the host system. Volumes are separate from the container's file system, which means that they can persist even if the container is deleted or recreated. Volumes can be used to store application data, configuration files, or any other type of data that needs to be shared between containers.

For example, let's say you have a database application that requires persistent storage. You can create a Docker volume that is mounted to the container's file system, and then store the database data in that volume. This way, even if the container is deleted or recreated, the data will still be available in the volume.

In summary, A Docker container is a running instance of a Docker image, Docker images are read-only templates that contain the instructions for creating a Docker container, and Docker volumes are a way to store and share data between Docker containers and the host system. Each component plays a crucial role in the Docker ecosystem, and understanding their differences is essential for building and deploying Docker applications.


## Getting Started with Docker
To get started with Docker, you need to follow these steps:

**Install Docker**: You can download and install Docker from the official Docker website for your operating system. Click Here

**Create a Dockerfile**: A Dockerfile is a configuration file that contains instructions for building a Docker image. You can create a Dockerfile in the root directory of your application.

Here is an example Dockerfile for a Node.js application:

```
FROM node:14-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD [ "npm", "start" ]
```

This `Dockerfile` uses the official `Node.js` image as the base image this can be done by using `FROM` keyword and then writing the name of the image, `WORKDIR` sets the working directory to /app. `COPY` copies the package.json and package-lock.json files. `RUN` installs the dependencies, COPY .. copies the application code(remember that you should always delete node_modules folder otherwise that will also get copied), `EXPOSE` exposes port 3000, and `CMD` starts the application using the npm start command.

**Build a Docker image**: To build a Docker image, you need to run the docker build command in the same directory as the `Dockerfile`. Here, `-t` flag means tag or we can say the name of the image.

```
docker build -t my-app .
```

This command builds a Docker image with the tag my-app using the `Dockerfile` in the current directory.

**Run a Docker container**: To run a Docker container, you need to run the docker run the command with the image name.

```
docker run -p 3000:3000 my-app
```

This command runs a Docker container with the image `my-app` and `-p` maps port 3000 of the container to port 3000 of the host machine.

That's it your image and your container is ready.

I hope this beginner's guide to Docker has been helpful in understanding the basics of Docker and how to get started with it. However, there is much more to learn about Docker, and we encourage you to explore the official Docker documentation for more information and advanced topics. You can find the official Docker documentation at docs.docker.com. Also, This was just part 1 on docker soon I will release part 2 where we will see a more practical approach using CLI and writing Dockerfile and much more, so make sure to subscribe to my newsletter.

Happy containerizing!

#docker #containerization