Post Date: December 28, 2018
Last Updated: October 03, 2026
Introduction
Docker Images and Containers are the foundation of modern application deployment and DevOps practices. Organizations today need applications to run consistently across development, testing, staging, and production environments. One of the biggest challenges in software deployment is ensuring that applications behave the same way regardless of where they are executed.
Docker solves this problem through containerization.
Docker is an open-source platform that enables developers and system administrators to package applications and all their dependencies into lightweight, portable containers. These containers can run reliably on any system with Docker installed, making deployments faster, more consistent, and easier to manage.
In this guide, you will learn Docker Images and Containers, how they work, how to pull images from Docker Hub, create containers, access running containers, and manage them efficiently.
Table of Contents
- What are Docker Images and Containers?
- What is Docker?
- What is a Docker Container?
- Benefits of Docker
- Prerequisites
- Creating Docker Images and Containers
- Useful Docker Commands
- Docker Images vs Containers
- Benefits of Containerization
- Frequently Asked Questions
- Conclusion
What are Docker Images and Containers?
Docker Images and Containers work together to provide a portable and consistent application runtime environment.
A Docker Image is a read-only template containing application code, libraries, dependencies, configuration files, and runtime components.
A Docker Container is a running instance of a Docker image.
Think of it this way:
- Docker Image = Blueprint
- Docker Container = Running Building
Multiple containers can be created from the same Docker image.
Docker Images and Containers Architecture
Docker Image
│
▼
Docker Container
│
▼
Running Application
What is Docker?
Docker is a containerization platform that packages an application along with its dependencies, libraries, configuration files, and runtime environment into a single unit called a container.
Using Docker Images and Containers ensures applications run consistently across multiple environments without compatibility issues.
Benefits of Docker
- Faster application deployment
- Environment consistency
- Lightweight resource usage
- Easy scalability
- Simplified dependency management
- Improved DevOps workflows
- Better CI/CD integration
- Reduced infrastructure overhead
Docker provides an excellent and efficient way to deploy applications consistently across environments.
What is a Docker Container?
A Docker Container is a lightweight, standalone, executable package that contains everything required to run an application.
Containers can be created, stopped, restarted, and removed whenever needed.
Examples include:
- Ubuntu Container
- CentOS Container
- Nginx Container
- Apache Container
- MySQL Container
- PostgreSQL Container
- PHP Application Container
Unlike traditional virtual machines, Docker containers share the host operating system kernel, making them significantly faster and more resource-efficient.
Why Use Docker Images and Containers?
Organizations worldwide use Docker Images and Containers because they provide:
Portability
Run applications anywhere without changing configurations.
Consistency
Applications behave identically across development, testing, and production environments.
Faster Deployment
Containers start within seconds compared to traditional virtual machines.
Scalability
Scale applications horizontally with minimal effort.
Isolation
Applications run independently without affecting each other.
Resource Efficiency
Containers consume fewer resources than virtual machines.
Prerequisites
Before creating Docker Images and Containers, ensure Docker is installed and running on your system.
Install Docker
Refer to our installation guide:
How to Install Docker in CentOS 7
Verify Available Disk Space
df -h
Sample Output:
Filesystem Size Used Avail Use% Mounted on /dev/xvda1 50G 12G 36G 25% /
Verify Docker Service Status
docker ps
Sample Output:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
Creating Docker Images and Containers
Step 1: Pull a CentOS Docker Image
docker pull centos:latest
Sample Output:
latest: Pulling from library/centos a02a4930cb5d: Pull complete Status: Downloaded newer image for centos:latest
Step 2: Verify Downloaded Docker Images
docker images
Sample Output:
REPOSITORY TAG IMAGE ID SIZE centos latest 1e1148e4cc2c 202MB
Step 3: Pull an Ubuntu Docker Image
docker pull ubuntu:latest
Sample Output:
latest: Pulling from library/ubuntu Status: Downloaded newer image for ubuntu:latest
Step 4: Verify Available Docker Images
docker images
Sample Output:
REPOSITORY TAG IMAGE ID SIZE centos latest 1e1148e4cc2c 202MB ubuntu latest 93fd78260bd1 86.2MB
Step 5: Create a CentOS Container
docker run -itd --name=xyz centos:latest /bin/bash
Sample Output:
667db752093100944df883d799a8d4f09564669f061362e614364d4a319e8529
Command Explanation
| Option | Description |
|---|---|
| docker run | Create and start container |
| -i | Interactive mode |
| -t | Allocate terminal |
| -d | Detached mode |
| –name | Assign custom name |
| /bin/bash | Launch Bash shell |
Step 6: Verify Running Containers
docker ps
Sample Output:
CONTAINER ID IMAGE COMMAND STATUS NAMES 667db7520931 centos:latest "/bin/bash" Up 9 sec xyz
Step 7: Create an Ubuntu Container
docker run -itd --name=abc ubuntu:latest /bin/bash
Step 8: Verify All Running Containers
docker ps
Sample Output:
CONTAINER ID IMAGE COMMAND STATUS NAMES 95dad75e0c6c ubuntu:latest "/bin/bash" Up 4 sec abc 667db7520931 centos:latest "/bin/bash" Up 57 sec xyz
Step 9: Access the CentOS Container
docker exec -it xyz /bin/bash
Step 10: Verify Operating System Details
cat /etc/os-release
Sample Output:
NAME="CentOS Linux" VERSION="7 (Core)" ID="centos" VERSION_ID="7"
Step 11: Exit the Container
exit
Verify running containers:
docker ps
Step 12: Access Ubuntu Container
docker exec -it abc /bin/bash
Step 13: Verify Ubuntu Version
cat /etc/os-release
Sample Output:
NAME="Ubuntu" VERSION="18.04.1 LTS (Bionic Beaver)"
Step 14: Exit Ubuntu Container
exit
Useful Docker Commands
View Running Containers
docker ps
View All Containers
docker ps -a
Stop a Container
docker stop xyz
Start a Container
docker start xyz
Restart a Container
docker restart xyz
Remove a Container
docker rm xyz
Remove an Image
docker rmi ubuntu
View Docker Version
docker version
View Docker Information
docker info
Docker Images vs Containers
| Feature | Docker Image | Docker Container |
|---|---|---|
| Type | Template | Running Instance |
| State | Static | Dynamic |
| Storage | Stored on Disk | Runs in Memory |
| Editable | No | Yes |
| Purpose | Create Containers | Run Applications |
| Example | ubuntu | abc |
Docker Images and Containers are closely related but serve different purposes. Images act as templates, while containers are the actual running environments created from those templates.
Benefits of Containerization
Containerization has become a standard practice in modern application deployment.
Portability
Applications run anywhere without modification.
Faster Deployments
Containers start within seconds.
Resource Efficiency
Containers share the host kernel and consume fewer resources.
Scalability
Applications can scale horizontally with ease.
Consistency
Docker Images and Containers ensure identical behavior across environments.
Isolation
Applications remain isolated from one another.
Improved CI/CD
Containers integrate seamlessly with modern CI/CD pipelines.
Best Practices for Docker Images and Containers
- Use official Docker images whenever possible.
- Keep container images lightweight.
- Avoid running applications as root.
- Remove unused containers regularly.
- Use Docker volumes for persistent data.
- Tag images properly.
- Scan images for vulnerabilities.
- Keep Docker updated.
Conclusion
Docker simplifies application deployment by packaging applications and their dependencies into lightweight, portable containers. Using Docker images and containers, developers and system administrators can quickly create isolated environments, improve deployment consistency, and reduce compatibility issues.
In this tutorial, we learned how to:
- Install and verify Docker
- Pull images from Docker Hub
- Create CentOS and Ubuntu containers
- Access running containers
- Verify operating system information
- Manage container lifecycle operations
Docker is a foundational technology for DevOps, cloud-native applications, CI/CD pipelines, microservices, and Kubernetes environments. Understanding these fundamentals provides a strong foundation for learning advanced Docker concepts such as custom images, Docker Compose, networking, volumes, and orchestration.
Frequently Asked Questions (FAQ)
1. What is Docker?
Docker is an open-source platform that enables developers to package applications and dependencies into portable containers.
2. What is a Docker Container?
A Docker container is a lightweight and isolated runtime environment used to run applications.
3. What is Docker Hub?
Docker Hub is a cloud-based repository used to store and distribute Docker images.
Related Articles
How to Convert a Docker Container to Image
How to Save Docker Images as a TAR File
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