What principles does Docker operate on?

Docker operates on the following key principles:

• Containerization: Isolation of applications and their dependencies into standardized, portable modules (containers).
• Images: Lightweight, standalone executable packages that include everything needed to run an application (code, libraries, system tools, configurations). They are built step-by-step using a Dockerfile.
• Layers: Images consist of layers. Each layer represents a set of changes in the filesystem. Layers are cached and can be reused by different images, saving space and speeding up build times.
• Isolation: Containers use Linux kernel isolation mechanisms (namespaces and cgroups) to separate processes, filesystems, networks, and other resources from the host system and other containers.
• Immutability of images: When a container is run from an image, the image itself does not change. All modifications inside the container occur in a writable layer on top of the base image, which is removed along with the container (if volumes are not used).
• Portability: A container developed and built in one environment can be run in any other environment where Docker is installed, without requiring additional dependency configurations on the host.
• Declarative approach: Dockerfile describes the image build process in a declarative style, making it reproducible and automatable.

Example Dockerfile:

# Use the Alpine Linux base image
FROM alpine:latest

# Install curl package
RUN apk add --no-cache curl

# Specify the command to run when the container starts
CMD ["curl", "https://www.example.com"]