Docker has transformed the way developers and IT teams deploy applications by providing a lightweight and consistent environment across different systems. Running Docker efficiently allows you to create, manage, and scale applications with minimal configuration.
In this guide, you will learn how to run Docker, work with Docker images, build and manage containers, use Docker Compose, and operate Docker on different platforms like Windows and macOS.
Understanding Docker and How It Works
Docker is a platform that enables developers to create, deploy, and run applications in isolated environments called containers. These containers package an application and all its dependencies, including libraries, system tools, and configurations, ensuring the application works uniformly across any environment. This eliminates the common "it works on my machine" problem, where an application behaves differently in development versus production environments.
Docker’s architecture consists of several core components that work together to make it easy to deploy and manage applications:
Docker Engine
The Docker Engine is the core service that runs Docker containers. It is a client-server application that consists of three main parts:
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Docker Daemon (dockerd) – This is the background service that manages Docker containers. It listens for Docker API requests and handles all aspects of container management, such as running containers, managing images, networks, and volumes.
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Docker CLI (Command-Line Interface) – This is the command-line tool used by developers and system administrators to interact with Docker Daemon. Common commands include docker run, docker ps, and docker build.
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Docker REST API – This allows users and other applications to communicate with the Docker Daemon programmatically.
Docker Images
Docker Images are read-only templates that contain everything needed to run an application, including the operating system, libraries, and the application itself. Think of them as blueprints for containers. Images can be built from a Dockerfile, which is a script of instructions on how the image should be created.
Once an image is built, it can be stored locally on the system or in a Docker registry such as Docker Hub. You can pull an image from the registry, modify it, or use it as-is to create a container.
Docker Containers
A Docker container is a running instance of a Docker image. Containers are isolated environments that share the host system’s kernel but are otherwise separate from other containers and the host system. This isolation makes them lightweight, fast, and portable.
Docker Compose
Docker Compose is a tool that simplifies managing multi-container applications. It allows you to define and run applications that require multiple containers, each with its own specific function (e.g., a web app, database, cache). Using a YAML configuration file (docker-compose.yml), developers can describe the services that make up their application, how they interact, and what environment variables they need.
Why Use Docker?
Docker has become a cornerstone in modern software development due to its numerous benefits, particularly for application deployment, testing, and scaling. Below are some key reasons why Docker is so widely used:
1. Provides a Lightweight Alternative to Virtual Machines
Virtual machines (VMs) are often used for isolation and running multiple environments on the same host. However, VMs require separate operating systems for each instance, leading to significant overhead in terms of disk space, memory, and CPU usage. Docker containers, on the other hand, share the host operating system’s kernel and isolate the application at the process level.
2. Ensures Portability Across Different Environments
Docker containers encapsulate everything an application needs to run, which makes it highly portable. Whether you are running an application on your local machine, a testing server, or in a production environment, Docker ensures it will work the same way.
3. Facilitates Scalability for Microservices Architectures
Docker is ideal for microservices architectures, where an application is broken down into multiple smaller, independent services. Each microservice can be packaged into its own container, which can then be deployed and scaled independently.
4. Improves Efficiency by Reducing System Overhead
Docker containers are highly efficient because they share the host system’s kernel and only contain the application code and dependencies necessary to run the app. This eliminates the need for virtualized operating systems in each container and allows containers to run with minimal resource overhead. Containers also start up much faster than VMs.
Installing Docker on Your System
Before you can start running Docker containers, you need to install Docker on your system. Docker can be installed on various platforms, including Linux, Windows, and macOS. Below are the steps on how to run Docker image locally on different systems.
How to Run Docker Image on Linux
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Update Your Package List
First, update your system's package list to ensure you have the latest information for available packages:
sudo apt update
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Install Docker
Install Docker using your system’s package manager. The following command installs Docker from the default Ubuntu repositories:
sudo apt install docker.io -y
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Enable and Start Docker
Enable Docker to start automatically at boot, and start the Docker service:
sudo systemctl enable --now docker
This will install Docker on a Linux machine running Ubuntu. To verify that Docker is running, you can use the command:
docker –version
How to Run Docker on Windows & macOS
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Windows:
To install Docker on Windows, you need to install Docker Desktop, which provides a graphical interface for managing Docker containers. You can download it from Docker’s official website. Docker Desktop integrates with Windows Subsystem for Linux (WSL 2) to provide a native Linux-based Docker experience.
After installation, you can verify the installation by running the following in PowerShell or the Command Prompt:
docker --version
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macOS:
On macOS, Docker can be installed using Homebrew or downloaded directly from the Docker website. If you use Homebrew, you can install Docker Desktop with the following command:
brew install --cask docker
Alternatively, you can download Docker Desktop directly from Docker’s official website. Once installed, you can start Docker from the Applications folder and use it from the terminal.
For detailed installation instructions, you can check out the article How to Install Docker.
How to Run Docker Containers
A Docker container is a running instance of an image. To start a container, use the docker run example command.
Basic Command to Run a Container
docker run hello-world
This command:
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Downloads the hello-world image (if not available).
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Runs the container, which prints a test message.
Running a Detached Container
To run a container in the background:
docker run -d nginx
Here, the -d flag ensures that the container runs in detached mode.
Running a Named Container
docker run --name mycontainer -d nginx
This assigns a custom name (mycontainer) to your container.
For more details on containers, see What is a Docker Image.
How to Run a Docker Image
Docker images are templates for containers. To pull and run an image:
Pull an Image
docker pull ubuntu
List Installed Images
docker images
Remove an Image
docker rmi ubuntu
To run a Docker image locally:
docker run -it ubuntu bash
This command launches an interactive Ubuntu container.
How to Run Dockerfiles
A Dockerfile is a script that defines how to build an image.
Example of a Dockerfile
Create a file named Dockerfile:
FROM python:3.8
WORKDIR /app
COPY . /app
RUN pip install -r requirements.txt
CMD ["python", "app.py"]
Build and Run the Image
docker build -t my-python-app .
docker run -p 5000:5000 my-python-app
How to Run Docker Compose
Docker Compose allows you to define multi-container applications.
Example docker-compose.yml
version: '3'
services:
web:
image: nginx
ports:
- "8080:80"
db:
image: mysql
environment:
MYSQL_ROOT_PASSWORD: password
Running Docker Compose
docker-compose up -d
For more on Docker’s orchestration capabilities, read What is Docker Swarm.
Managing the Docker Daemon
The Docker Daemon runs in the background and manages containers.
Start the Daemon
sudo systemctl start docker
Stop the Daemon
sudo systemctl stop docker
Restart Docker
sudo systemctl restart docker
For macOS, start the daemon manually:
dockerd &
Running Docker on Windows and macOS
How to Run Docker on Windows
Docker requires Windows Subsystem for Linux (WSL 2) for full functionality. After installing Docker Desktop:
docker run -d -p 80:80 nginx
Running Docker on macOS
Ensure Docker is installed, then start a container:
docker run -d -p 80:80 nginx
Running Docker as a Non-Root User
By default, Docker runs with root privileges. To allow a non-root user to run Docker:
sudo usermod -aG docker $USER
newgrp docker
Now, you can run Docker commands without sudo:
docker run hello-world
Conclusion
Running Docker is straightforward with the right setup. From installing Docker to managing containers, images, and Docker Compose, this guide provides everything you need to get started.
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