Using Docker on Linux: From Installation to Deployment

Introduction

Docker has revolutionized the way we develop, deploy, and manage applications. By packaging software into standardized units called containers, Docker allows you to run applications consistently across different environments. This tutorial will guide you through using Docker on Linux, from installation to deploying your first containerized application.

Section 1: Introduction to Docker

1.1 What is Docker?

Docker is an open-source platform that automates the deployment of applications inside lightweight, portable containers. Containers include everything an application needs to run, such as libraries, dependencies, and configurations, ensuring that it behaves the same regardless of where it is deployed.

1.2 Why Use Docker?

• Consistency: Docker containers ensure that applications run the same way across different environments.

• Efficiency: Containers are lightweight and share the host OS kernel, making them more resource-efficient than virtual machines.

• Scalability: Docker makes it easier to scale applications, allowing you to deploy multiple containers across a cluster.

Section 2: Installing Docker on Linux

2.1 Prerequisites

Before installing Docker, ensure your Linux distribution is up-to-date:

sudo apt-get update
sudo apt-get upgrade

2.2 Installing Docker on Ubuntu

To install Docker on Ubuntu, follow these steps:

• Install Docker Dependencies:

sudo apt-get install apt-transport-https ca-certificates curl software-properties-common
   

• Add Docker’s Official GPG Key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
   

• Add the Docker Repository:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
   

• Install Docker:

sudo apt-get update
   sudo apt-get install docker-ce
   

• Verify Docker Installation:

sudo systemctl status docker
   

You should see Docker running.

2.3 Installing Docker on CentOS

To install Docker on CentOS:

• Remove any old Docker versions:

sudo yum remove docker docker-common docker-selinux docker-engine
   

• Install Required Packages:

sudo yum install -y yum-utils device-mapper-persistent-data lvm2
   

• Add the Docker Repository:

sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
   

• Install Docker:

sudo yum install docker-ce
   

• Start Docker:

sudo systemctl start docker
   

• Enable Docker to Start at Boot:

sudo systemctl enable docker
   

• Verify Installation:

sudo docker --version
   

Section 3: Basic Docker Commands

3.1 Running Your First Container

To run a simple Docker container using the hello-world image:

sudo docker run hello-world

This command downloads the hello-world image from Docker Hub (if not already available) and runs it in a container.

3.2 Listing Docker Containers

To list running containers:

sudo docker ps

To list all containers (running and stopped):

sudo docker ps -a

3.3 Stopping and Removing Containers

To stop a running container:

sudo docker stop container_id

To remove a stopped container:

sudo docker rm container_id

Section 4: Working with Docker Images

4.1 Pulling Images from Docker Hub

Docker Hub is a cloud-based repository where you can find container images. To pull an image:

sudo docker pull ubuntu

This command downloads the official Ubuntu image.

4.2 Building Custom Docker Images

To build a custom Docker image, you need to create a Dockerfile. Here's an example:

# Use an official Ubuntu as a parent image
FROM ubuntu:latest

# Install necessary packages
RUN apt-get update && apt-get install -y nginx

# Expose port 80
EXPOSE 80

# Start Nginx when the container launches
CMD ["nginx", "-g", "daemon off;"]

Build the Docker image using the following command:

sudo docker build -t my-nginx-image .

This command builds an image from the Dockerfile in the current directory and tags it as my-nginx-image.

4.3 Pushing Images to Docker Hub

To push an image to Docker Hub:

• Log in to Docker Hub:

sudo docker login
   

• Tag the Image:

sudo docker tag my-nginx-image your-dockerhub-username/my-nginx-image
   

• Push the Image:

sudo docker push your-dockerhub-username/my-nginx-image
   

Section 5: Deploying Applications with Docker

5.1 Deploying a Web Application

Let's deploy a simple web application using Docker.

• Create a Dockerfile:

FROM python:3.8-slim

   WORKDIR /app

   COPY requirements.txt requirements.txt
   RUN pip install -r requirements.txt

   COPY . .

   EXPOSE 5000

   CMD ["python", "app.py"]
   

• Build the Docker Image:

sudo docker build -t my-python-app .
   

• Run the Docker Container:

sudo docker run -d -p 5000:5000 my-python-app
   

This command runs your Python web application in a container and maps port 5000 on the host to port 5000 in the container.

• Access the Application:

Open your web browser and navigate to http://localhost:5000 to see your web application in action.

5.2 Using Docker Compose for Multi-Container Applications

Docker Compose is a tool that allows you to define and manage multi-container Docker applications.

• Create a docker-compose.yml file:

version: '3'
   services:
     web:
       image: my-python-app
       ports:
         - "5000:5000"
     redis:
       image: "redis:alpine"
   

• Start the Multi-Container Application:

sudo docker-compose up
   

• Stop the Application:

sudo docker-compose down
   

Section 6: Managing Docker Volumes and Networks

6.1 Working with Docker Volumes

Volumes are used to persist data generated by Docker containers. To create a volume:

sudo docker volume create my-volume

To use this volume in a container:

sudo docker run -d -v my-volume:/app/data my-python-app

6.2 Configuring Docker Networks

Docker networks allow containers to communicate with each other. To create a custom network:

sudo docker network create my-network

To run a container on this network:

sudo docker run -d --network=my-network my-python-app

Conclusion

Docker simplifies the process of deploying, managing, and scaling applications by using containers. From installation to deployment, mastering Docker on Linux opens up a world of possibilities for application development and system management. By following this guide, you'll be well on your way to becoming proficient in using Docker to streamline your development and operations workflows.