Learn how Docker images are built, structured, tagged, stored, and distributed. Understand image layers, Dockerfiles, base images, registries, and practical image management.
Docker Image Learning Path
Understanding Images
Image Layers
Base Images
Dockerfiles
Image Tags
Container Registries
Introduction
A Docker image is a standardized package that contains the files, binaries, libraries, dependencies, and configuration required to run a containerized application.
Images are immutable. Instead of directly modifying an existing image, changes are typically made by building a new image or by adding additional layers.
Docker images are used as templates for creating containers, allowing applications to run with a consistent set of dependencies and configuration across different environments.
Core Concepts
Learn the core concepts required to understand, build, manage, tag, and distribute Docker images.
A Docker image is a packaged template containing the files, dependencies, libraries, configuration, and application components required to create and run containers.
Key Topics
Docker images are built from layers. Each build instruction can create filesystem changes that become part of the resulting image.
Key Topics
A base image provides the starting environment for building a custom container image.
Key Topics
Dockerfiles define the instructions used to build Docker images, including the base image, files, dependencies, environment, and startup command.
Key Topics
Tags provide a readable name or version reference for a Docker image and help identify different versions or variants.
Key Topics
Container registries store and distribute Docker images so they can be pulled, shared, and deployed across different environments.
Key Topics
Command Line
Learn commonly used commands for listing, pulling, building, inspecting, tagging, removing, and publishing Docker images.
docker image lsList Docker images available on your local system.
docker pull nginxDownload a Docker image from a container registry.
docker build -t my-app:latest .Build a Docker image from a Dockerfile and assign it a name and tag.
docker image inspect nginxDisplay detailed information about a Docker image.
docker image history nginxDisplay the history and layers associated with a Docker image.
docker tag my-app:latest my-app:v1Create a new tag that refers to an existing Docker image.
docker image rm my-appRemove a Docker image from the local system.
docker push username/my-app:latestUpload a tagged Docker image to a configured container registry.
Building Images
A Dockerfile is a text-based file containing instructions used to build a container image. It can define the base image, working directory, application files, dependencies, environment variables, exposed ports, and startup command.
Docker processes the instructions to build the final image, which can then be tagged and used to create containers.
Example Dockerfile
FROM node:22-alpine WORKDIR /app COPY package*.json ./ RUN npm install COPY . . EXPOSE 3000 CMD ["npm", "start"]
Common Dockerfile Instructions
FROMDefines the base image used as the starting point for a new image.
WORKDIRSets the working directory for subsequent Dockerfile instructions.
COPYCopies files and directories from the build context into the image.
RUNExecutes commands during the image build process.
ENVSets environment variables that can be used by the application or runtime.
EXPOSEDocuments the network port that the application expects to use.
USERSets the default user for subsequent instructions and container execution.
CMDDefines the default command that runs when a container starts from the image.
Image Lifecycle
Docker images can be pulled from registries or built locally from a Dockerfile. Once created, an image can be tagged with a version or repository name and pushed to a registry for distribution.
Other users, systems, or deployment environments can then pull the image and use it to create containers.
Typical Docker Image Lifecycle
Tags & Registries
Image names can include a registry host, namespace, repository, and tag. Tags help identify versions or variants of an image, while registries provide storage and distribution for images.
Docker image references can identify the registry, namespace, repository, and optional tag.
username/my-app:latestTags provide readable identifiers that can represent application versions, releases, environments, or image variants.
my-app:v1.0Registries store Docker images and allow teams and systems to distribute, pull, and deploy them across environments.
docker push username/my-appLearning Roadmap
Follow this learning path to understand Docker images and build practical container image skills.
Learn what Docker images contain and how they provide a consistent environment for running applications.
Search for and pull existing images from a container registry and inspect their local metadata.
Understand how Docker images are composed of layers and how build instructions contribute to the final image.
Create a Dockerfile that defines a base image, application files, dependencies, configuration, and startup command.
Build custom images and use tags to create meaningful names and version references.
Tag and push an image to a container registry so it can be shared and deployed.
Continue Learning
Understand the difference between Docker images and containers and learn how they work together.
📄Learn how to create a Dockerfile and build your own custom container image.
⚙️Learn how to define and run multi-container applications with Docker Compose.
Next Step
Continue learning Dockerfiles, containers, Docker Compose, networking, volumes, Kubernetes, and modern container technologies.