K8S Notes

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Building Container Images

• Container Naming Metaphor:
  • The term “container” in technology is metaphorically borrowed from standardized shipping containers (ISO 668).
  • Similar to shipping containers, standardized format facilitates stacking, unloading, and transporting with ease.
• Nautical Theme in Container Technology:
  • Many terms in the container and cloud-native domain draw from the nautical theme inspired by shipping containers.
• Docker’s Component Reuse:
  • Docker leverages existing components like namespaces and cgroups to isolate processes.
• Crucial Breakthrough:
  • Introduction of container images is pivotal for containers.
  • Container images ensure portability and ease of reuse on diverse systems.
• Docker’s Definition of Container Images:

  • Docker defines a container image as:

    “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.”

• OCI Image-Spec:
  • In 2015, Docker’s popular image format was contributed to the Open Container Initiative (OCI).
  • Known as OCI image-spec, it’s available on GitHub.
  • Images consist of a filesystem bundle and metadata.
• Container Images:
  • Images are constructed using a buildfile called Dockerfile.
  • Dockerfile instructions mimic those for installing an application on a server.

• Example Dockerfile for Python Script:

    # Base image selection
    FROM ubuntu:20.04
  
    # Software and libraries installation
    RUN apt-get update && \\
        apt-get -y install python3 python3-pip
  
    # Copying code to the image
    COPY my-app.py /app/
  
    # Defining the working directory
    WORKDIR /app
  
    # Starting process when the container runs
    CMD ["python3","my-app.py"]
  

• Building Image with Docker:

  • Command for building the image:

      docker build -t my-python-image -f Dockerfile
    

  • Parameters:

    • t my-python-image: Specifies a name tag for the image.
    • f Dockerfile: Specifies the location of the Dockerfile.
• Dependency Management by Developers:
  • Developers manage application dependencies and package it for execution.
  • This approach empowers developers to handle dependencies, ensuring a self-contained and runnable package.
• Distribution via Container Registry:
  • Images can be distributed using a container registry, a web server for uploading and downloading images.

  • Docker provides built-in commands for pushing and pulling images from the registry:

    docker push my-registry.com/my-python-image
    docker pull my-registry.com/my-python-image
    

Container Orchestration