Docker Image vs. Container: What Are the Differences?

You may have heard the terms Docker Image or Docker Container if you're new to Docker. They may look similar at first but their purposes are different. Anyone working with containerized apps must understand their differences. This article will explore Docker Images and Docker Containers. We will also look at their roles and how they work together.

What is Docker Image?

A Docker Image can be compared to a blueprint for creating Docker containers. A Docker Image is a lightweight package, which can be run independently, that includes everything required to run an app, including:

The application code
Runtime environment
Libraries and Dependencies
Tools and Settings for System Software

Docker Images cannot be altered once they are created. You can create new Docker images by editing existing images and saving them in new versions. These images are stored on Docker registries such as Docker Hub and private repositories.

Key characteristics of Docker images:

Docker Images can only be read-only once they have been built.
Version-controlled: Multiple images can be created, with the option to roll back to an earlier version.
Portable: They are easily shared between different environments and ensure consistency.
Images are stored in a registry: Docker Hub or AWS ECR (or private registries) store and distribute images.

What is a container?

A Docker Container runs a Docker image. Imagine it as the real-world implementation. Containers are created by converting an image into a container that provides an isolated environment for running applications without affecting host systems.

Containers are lighter than traditional virtual machines because they use the OS kernel of the host instead of running a separate OS. They are faster and more efficient.

The Docker Container:

Containers can be deleted or restarted, they are not permanent.
Isolated: Every container operates in its own area without interfering with the other containers.
Stateful or stateless: Containers may be designed to either store persistent data or run stateless apps.
Can be stopped and restarted: If a container has been stopped, the state of that container is lost.

What is the difference between Docker Image Container and Docker Container?

Features	Docker Image	Docker Container
Definition	Template with all dependencies, configurations and settings to create a container	Docker image running
State	Static and immutable	Dynamic and Mutable
Stores	Docker registers are used to store the registries.	Runs in memory, unless persistent
Execution	Direct execution is not possible	Runs is an isolated process
Changes	Once created, the file cannot be altered	If you do not commit to the changes made during runtime, they will be lost upon restart.
Lifespan	Storage of goods for an indefinite period	Exists only when running

Docker Image and Containers Work Together

Building an Image: Developers build a Dockerfile to define the image. This includes the OS, dependencies and application code.
Creating an image: Docker build creates a Docker image.
Running a Container : Docker run is used to create an image-based container.
Containers can be stopped, started or removed at any time.
Persisting changes: If you need to save any changes, you can commit a modified image as a brand new one using docker.

The conclusion of the article is:

Docker Images and Containers have a close relationship, but they serve different roles. A Docker Image is like a blueprint while a Docker Container runs the blueprint. Understanding the differences between them is crucial for containerized application deployment and development.

For those looking to deepen their knowledge, Docker training online can provide valuable insights and hands-on experience. Developers and DevOps Engineers can build scalable, portable, and consistent applications by mastering these concepts. Knowing the difference between an image and a container is important, whether you're just starting out with Docker or trying to optimize your workflow.