Essential Docker Concepts Every DevOps Engineer Should Master for Interviews

Container:
A lightweight, standalone, and executable software package that includes everything needed to run an application (code, runtime, system tools, libraries).

Image:
A read-only template used to create containers. Images are built from Dockerfiles and can be stored in a registry.

Dockerfile:
A script with a set of instructions to create a Docker image. It defines the base image, application code, dependencies, and configuration.

Docker Compose:
A tool to define and run multi-container Docker applications using a YAML file (docker-compose.yml). It simplifies running complex environments.

Volume:
A mechanism for persisting data generated and used by Docker containers, ensuring data is not lost when a container stops.

Bind Mount:
Directly connects a directory on the host system to a directory in the container, allowing changes in either to be reflected in both.

Registry:
A centralized location where Docker images are stored and distributed, such as Docker Hub or a private registry.

Layer:
Images are made up of layers, which are stacked to form a final image. Each command in a Dockerfile creates a new layer.

Tag:
A version identifier for Docker images, typically used to differentiate between versions of an image (e.g., nginx:latest, nginx:1.19).

Entrypoint:
A command or script that always runs when a container starts. It defines the main process within the container.

CMD:
Specifies the default command to run inside a container. It can be overridden when starting the container.

Expose:
Defines which ports the container listens to, allowing communication between containers or from the host.

Docker Network:
Allows containers to communicate with each other. Types include Bridge, Host, and Overlay networks.

Docker Swarm:
A native clustering and orchestration tool for Docker. It manages a cluster of Docker engines and allows container scheduling across nodes.

Docker Engine:
The core component of Docker that runs and manages containers. It includes the Docker daemon, REST API, and CLI.

Build Context:
The directory that contains the Dockerfile and associated files, sent to the Docker daemon during the image build process.

Multistage Build:
A feature that allows multiple FROM statements in a Dockerfile, improving efficiency by reducing image size and separating build and runtime environments.

Container Registry:
A service to store and distribute Docker images. Examples include Docker Hub, Amazon ECR, and Google Container Registry (GCR).

Health Check:
A mechanism to test whether the application inside a container is healthy and ready to accept traffic.

Orchestration:
Using a tool like Kubernetes or Docker Swarm to manage containers, ensure high availability, scaling, and service discovery.

These terms showcase a strong understanding of Docker's core components and best practices for containerization.