Docker images: from Docker Hub to your own containers

Many developers start by pulling an image from Docker Hub. With just a few commands you can run a database, a web server or a complete development environment.

But once you begin building your own images, managing volumes and deploying containers across environments, Docker quickly becomes more complex.

Understanding how Docker images work is therefore a key part of modern DevOps workflows.

What is a Docker image?

A Docker image is a template that contains everything an application needs to run:

• runtime environment
• libraries and dependencies
• configuration and environment variables.

When an image is executed, it becomes a container – an isolated environment where the application runs independently of the host system.

This ensures that the application behaves the same way in development, testing and production environments, eliminating the classic problem:

"But it worked on my machine."

Images are built in layers

Docker images are built using layers. Each instruction in a Dockerfile creates a new layer in the image.

Docker can cache these layers and reuse them in future builds, which significantly speeds up the build process.

This layered architecture makes images:

• reusable
• versionable
• efficient to distribute.

Using pre-built images

Docker Hub and other registries provide thousands of ready-made images for common tools such as MySQL, Node.js and Redis.

Using pre-built images allows teams to quickly start applications or environments without installing and configuring everything from scratch.

It also improves consistency. When everyone uses the same base image, environments behave the same across development, testing and deployment.

In practice, many teams use these images as a starting point and extend them with their own custom images.

Building your own images

Custom images are typically created using a Dockerfile, which defines:

• the base image
• additional packages and dependencies
• how the application should start.

This allows teams to create standardised environments for development, testing and deployment.

Once built, images can be stored in registries such as Docker Hub or private repositories, making them easy to reuse and share within an organisation.

From containers to orchestration

Modern applications rarely consist of a single container. Instead they often include multiple services that need to run together.

Tools such as:

• docker-compose help orchestrate multiple containers locally
• Kubernetes enables teams to deploy, scale and monitor containerised applications in cloud environments.

Docker images form the foundation of this container-based architecture.