What is Docker Images
Docker Image Architecture
Structure Of Docker Image
Explain different type of docker image in registry and their role
A Docker container image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings
Docker image is an executable package of software that includes everything needed to run an application
- Docker images are immutable, they can't be changed.
- Docker images can be duplicated, shared or deleted.
- Docker image also act as the starting point when using Docker. 5. Docker image contains appication code, libraries, tools, dependencies and other files needed to make an application run. 6. Docker images have multiple layers, each one originates from the previous layer but is different from it.
- Docker images are a reusable asset deployed o any host.
- Docker images has many layers such as base image, parent image, layers, container layer, docker manifest.
- Docker image informs how a container should instantiate which software components will run and how 10.Docker image informs how a container should determining which software components will run and how
Docker Image is an executable package of software that includes everything needed to run an application. This image informs how a container should instantiate, determining which software components will run and how. Docker Container is a virtual environment that bundles application code with all the dependencies required to run the application. The application runs quickly and reliably from one computing environment to another.
Uses of Docker Images
- We can easily and effectively run the containers with the aid of docker images.
- All the code, configuration settings, environmental variables, libraries, and runtime are included in a Docker image.
- Docker images are platform-independent.
- Layers are the building blocks of an image.
- WithWhen using the build command, the user has the option of completely starting from scratch or using an existing image for the first layer
Difference between Docker Image and Docker Container
The layers of software that make up a Docker image make it easier to configure the dependencies needed to execute the container.
Base Image: The basic image will be the starting point for the majority of Dockerfiles, and it can be made from scratch.
Parent Image: The parent image is the image that our image is based on. We can refer to the parent image in the Dockerfile using the FROM command, and each declaration after that affects the parent image.
Layers: Docker images have numerous layers. To create a sequence of intermediary images, each layer is created on top of the one before it.
Docker Registry: Refer to this page on the Docker Registry for further information.
Docker images are snapshots of a file system, along with metadata and configuration details, that form the basis of containers. These images can be stored in container registries, which are repositories for managing and distributing container images. Here are different types of Docker images commonly used in container registries:
Role: Base images serve as the foundation for other images. They contain the essential components needed to run an application but lack specific application code or dependencies.
Example: alpine, ubuntu, and centos are commonly used base images.
docker pull alpine:latest
Role: These are curated and maintained by the upstream communities (like Alpine, Ubuntu, etc.) or by the organizations behind the software. They are generally considered reliable and secure.
Example: nginx, postgres, and python official images are available on Docker Hub.
docker pull nginx:latest
Role: Custom images are created by users to package and distribute their applications along with their dependencies. These images often start with a base image and add application-specific configurations and code.
Example: If you have a Python web application, you might start with the official python image and then add your application code and necessary dependencies.
docker build -t my-python-app .
Multi-Stage Build Images:
Role: These images are used to optimize the size of the final production image by building in multiple stages. The first stage can include build tools and dependencies, and the final stage contains only the necessary artifacts for runtime.
Example: A Go application might have one stage for compiling the code and another for running the compiled binary, resulting in a smaller image.
docker build -t my-go-app .
Role: Builder images are used for building applications or libraries but not necessarily for running them. They often contain build tools, compilers, and other necessary components.
Example: An image containing a full development environment with compilers and build tools, used for compiling software before being packaged into a smaller runtime image.
docker build -t my-builder .
Slim and Alpine Images:
Role: These images are designed to be lightweight by using minimalistic base images. Alpine Linux-based images, in particular, are known for their small size.
Example: The official nginx:alpine image is a slim version of Nginx based on Alpine Linux.
docker pull nginx:alpine
Role: Scratch is a special empty image that can be used as a starting point for building minimalistic images. This is often used for building completely static binaries.
Example: Images for some Go applications might start with a scratch image to create minimalistic, standalone binaries.
docker build -t my-minimal-app -f Dockerfile.scratch .
When using container registries like Docker Hub or a private registry, these images can be stored, versioned, and shared among teams. Understanding the types of images and their roles helps in creating efficient, secure, and manageable containerized applications.
# Use a scratch image
# Copy the statically compiled binary into the image
COPY myapp /
# Set the binary as the entry point