Docker Image vs Docker Container – Differences with Examples

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Docker images and Docker containers are core concepts every Docker beginner must understand.

In simple terms, a Docker image is a read-only template, while a Docker container is a running instance created from that image.

In this guide, you’ll learn: - What a Docker image is - What a Docker container is - Key differences between images and containers - Real Docker examples using Ubuntu

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What is a Docker Image?

A Docker image is a lightweight, immutable, read-only template that contains everything required to run an application: - Application code - Runtime - Libraries - Dependencies

Docker images are used as blueprints to create containers.

All Docker images are stored in a Docker registry, most commonly Docker Hub.

👉 Docker Hub: https://hub.docker.com

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What is a Docker Container?

A Docker container is a running instance of a Docker image.

When a container is created: - The image stays unchanged (read-only) - A writable layer is added on top - The application starts running

If the container stops, the image remains intact.

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Docker Image vs Docker Container – Comparison Table

Feature	Docker Image	Docker Container
Nature	Static	Dynamic
State	Read-only	Read-write
Purpose	Blueprint	Running application
Created using	Dockerfile	docker run
Stored in	Docker registry	Host system
Lifecycle	Does not run	Can start, stop, restart

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ISO Image vs Docker Image (Easy Analogy)

An ISO image is a static installation file. Applications run only after the operating system is installed and started.

Similarly: - A Docker image is a static package - A Docker container runs applications from that image

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Pulling Docker Images from Docker Hub

Check existing images on the server:

docker image ls

Pull the Ubuntu image:

docker pull ubuntu

By default, Docker pulls the latest tag.

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Pulling a Specific Image Tag

Docker images follow this format:

IMAGE_NAME:TAG

Example:

docker pull ubuntu:23.10

Verify images:

docker images

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Creating a Docker Container from an Image

Create a container using the Ubuntu image:

docker run -it ubuntu:23.10 bash

Inside the container:

pwd
ls
id
cat /etc/os-release

This confirms that the container is running Ubuntu 23.10 using the image.

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Image and Container Relationship

• One image ➜ multiple containers
• Containers can be stopped or removed
• Images remain unchanged

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FAQs

Is a Docker container an image?

No. A Docker container is created from an image and represents a running process.

Can one Docker image create multiple containers?

Yes. A single image can be used to create multiple containers.

What happens when a container stops?

The container stops running, but the image remains unchanged.

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Next Steps

👉 What is Docker?
👉 How to Install Docker on Linux

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🧠 Quick Quiz — Docker Image vs Container

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Which of the following statements is true?

A Docker image is read-only, and a container is the runnable instance.

A Docker container is read-only, and an image is the runnable instance.

Images and Containers are exactly the same thing.

You can edit a Docker image directly while it's running.

The Docker image is the static, read-only template, while the container is the dynamic, running instance created from that image.

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When you delete a Docker container, what happens to the image it was created from?

Nothing, the image remains unchanged.

The image is also deleted.

The image becomes corrupted.

The image is moved to the Trash.

Images are immutable templates. Deleting a running instance (container) does not affect the template (image) used to create it.

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Can you create multiple containers from a single Docker image?

Yes, as many as your system resources allow.

No, only one container per image.

Yes, but only up to 3 instances.

No, you must clone the image first.

A single image can act as a blueprint to launch any number of identical containers, just like a single class can instantiate multiple objects in programming.

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Important Tips

Tip

Immutability: Think of Docker images like a CD-ROM or a read-only ISO file. You can't change the data on it once it's burned (built). To change the application, you must build a new image.

Note

Layers: Docker uses a layered file system. When you start a container, Docker simply adds a thin, writable layer on top of the read-only image layers. This makes starting containers extremely fast and storage-efficient.

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📝 Want More Practice?

👉 Test your knowledge – Take the Docker Basics Quiz

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