Kubernetes & Docker

Master Kubernetes & Docker for software engineering interviews. Docker Fundamentals Docker is a containerization platform that packages applications and their dependencies into isolated, portable units called containers. Unlike virtual machines, containers share the host kernel — making them lightweight, fast to start, and efficient. Core Concepts Image: An immutable, layered read-only template. Think of it as a class definition. Container: A running instance of an image. Think of it as an object instantiated from a class. Layer: Each instruction in a Dockerfile creates a new read-only layer. Layers are cached and shared between images. Registry: A storage and distribution system for images. Docker Hub is the public default; AWS ECR, GCR, and GHCR are popular private options. Your First Dockerfile — Node.js API Multi-Stage Build — Production Best Practice Multi-stage builds let you use a fat builder image to compile/bundle, then copy only the artifacts into a slim runtime image. This dramatically reduces final image size. Result: A 1.2 GB builder image becomes a 180 MB production image. The build tools, source maps, TypeScript compiler, and dev dependencies are all discarded. Dockerfile Instructions Reference Purpose Base image Set working directory Copy files from host Like COPY can extract tarballs Execute command in new layer Set environment variable Build-time variable Document network port Set running user Default command (overridable) Fixed entry point Container health probe Declare mount point Python Example — FastAPI Application Layer Caching — The Golden Rule Docker processes Dockerfile instructions top-to-bottom. When a layer changes, all subsequent layers are invalidated. The strategy is: least-frequently-changing instructions first. The .dockerignore File Always create to prevent bloating the build context: Essential Docker CLI Commands Interview Talking Points "I always use multi-stage builds in production to minimize image size and attack surface." "Layer caching is the biggest Dockerfile performance lever — I order instructions from least to most frequently changing." "I run containers as non-root and use HEALTHCHECK so orchestrators know if the app is actually ready." "The difference between CMD and ENTRYPOINT: CMD can be overridden at runtime, ENTRYPOINT cannot. I use ENTRYPOINT for the binary and CMD for default arguments." Java Implementation Python Implementation