Docker Containerization

Docker containerization wraps an application along with its runtime, libraries, and configuration into a standardized unit called a container. Unlike virtual machines, containers share the host OS kernel, making them lightweight and fast to start. Each container runs in its own isolated namespace with its own filesystem, process tree, and network stack, ensuring consistent behavior across development, staging, and production environments.

Containers solve the classic 'works on my machine' problem by encoding the entire runtime environment into an image that can be versioned, shared, and deployed identically everywhere. Docker uses a layered filesystem (OverlayFS) where each instruction in a Dockerfile creates a new read-only layer, and a writable layer is added at runtime. This architecture enables efficient caching, fast image pulls through layer deduplication, and minimal disk usage when multiple containers share base layers.

In production, containers are typically run with resource constraints (CPU limits, memory limits), health checks, and restart policies. Docker's networking model supports bridge, host, overlay, and macvlan modes, allowing flexible service-to-service communication. Container logging is captured from stdout/stderr and can be routed to centralized logging systems via logging drivers.