What is the Difference Between Docker Images and Docker Containers?

Docker revolutionized app development by offering consistency and portability. However, differentiating between Docker Images and Docker Containers is essential to learning this powerful tool.

In this guide, we’ll explore these two concepts in depth, helping you gain clarity while leveraging Docker in your development workflows. We’ll point you to other helpful resources to expand your knowledge of server management, Linux tools, and more.

1. What is a Docker Image?

Docker Images are lightweight, portable, and executable packages that encapsulate everything required to run a specific application, including:

• Application code
• System libraries
• Dependencies
• Environment variables

Docker images are static and immutable, acting as blueprints for creating containers. They can be considered snapshots of an application in a particular state.

Creating Docker Images

To create a Docker image, you write a Dockerfile, specifying instructions such as the base image, application code, and dependencies. For example:

FROM python:3.9-slim
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

I am running docker build -t my-python-app . Generates an image named my-python-app.

Related Resources:

• Learn how to install Docker on CentOS Stream 9 to get started with Docker on a reliable Linux distribution.

2. What is a Docker Container?

A Docker Container runs a Docker Image. It’s the operational version of the application, running in an isolated environment. Containers provide lightweight virtualization, sharing the host system’s OS kernel while maintaining complete application isolation.

Running Containers

Create containers with docker run. For example:

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

This runs the application defined in the my-python-app image, mapping port 5000 on the host to port 5000 in the container.

Related Resources:

• If you’re setting up a server to host applications, check out how to install and use Ollama and OpenWebUI on your VPS for alternative tools.

• Learn to install and set up Coolify for a smooth DevOps experience.

​​

3. Key Differences Between Docker Images and Containers

Aspect	Docker Image	Docker Container
Definition	Blueprint/template for an application.	Running instance of a Docker image.
State	Static and immutable.	Dynamic and mutable.
Purpose	Defines the environment.	Executes the environment.
Storage	Stored on disk or registry.	Runs in memory; persists data if volumes are used.
Scalability	One image can spawn multiple containers.	Each container is an independent instance.

4. Managing Docker Images and Docker Containers

Managing Docker images and containers is simple with Docker’s command-line tools. Below are some useful commands:

Managing Images

• List all images: docker images
• Remove an image: docker rmi <image_id>
• Get an image: docker pull <image_name>

Managing Containers

• List running containers: docker ps
• Stop a container: docker stop <container_id>
• Remove a container: docker rm <container_id>
• Access container logs: docker logs <container_id>

5. Using Docker with Linux Servers

Docker thrives on Linux-based servers due to its lightweight nature and integration with Linux kernel features. When you combine Docker with a properly configured Linux environment, setting up user permissions, file sharing, and application hosting becomes easier.

Useful Guides:

• Learn how to add a user to a Linux group for better permission management when working with Docker.

• Discover how to install and use Filestash to manage files on your server.

• Explore Automatisch, a self-hosted workflow automation tool that complements Docker environments.

6. Practical Use Cases

Docker images and containers are designed to work together but serve different purposes:

Docker Images:

• Portability: Build once, run anywhere.
• Version Control: Easily manage application versions.
• Sharing: Push to a Docker registry for collaboration.

Docker Containers:

• Testing and Debugging: Run isolated environments for testing.
• Scaling: Deploy multiple containers from a single image to handle traffic spikes.
• Development: Create sandboxed environments for development projects.

7. Common Questions and Misconceptions

Are images and containers the same?

No. Docker images are templates, while containers are running instances of those templates.

Can I modify a Docker image directly?

No. To make changes in your Docker Image, you must create a new image based on the original using a new Dockerfile or by committing changes from a container.

How can I store data in containers?

You can store data outside the container’s temporary filesystem using Docker volumes.

8. Conclusion

Thinking of them as read-only templates is critical to leveraging Docker. Images provide the blueprint, while containers are the live, operational environments built from those images. Together, they form the backbone of Docker’s capabilities.

Expand Your Knowledge:

• Set up Docker on CentOS Stream 9 with this guide.
• Explore tools like Coolify and Automatisch to increase your server’s capabilities.
• Manage server files and Provide Cloud Storage using Filestash.
• Fine-tune user permissions with this Linux group guide.

You can optimize your Docker workflows and server management practices by combining this knowledge with practical tools and techniques.

About the writer

Vinayak Baranwal wrote this article. Use the provided link to connect with Vinayak on LinkedIn for more insightful content or collaboration opportunities.