Containers

Docker

Docker is one of the most important tools in modern DevOps. It allows teams to package applications and their dependencies into containers that run consistently across different environments. This reduces environment drift and makes shipping software much easier.

ContainersImagesRuntime

Key Concepts

Docker images are immutable templates used to start containers.

Containers are lightweight isolated processes sharing the host kernel.

Volumes are used to persist data outside the container lifecycle.

Docker networks allow communication between containers and external systems.

Common Interview Questions

What is the difference between a Docker image and a container?

What is the difference between CMD and ENTRYPOINT?

Why are Docker volumes important?

Use Case

Use Docker to create consistent environments across local development, CI pipelines, and production.

Common Use Cases

Packaging web applications and APIs into deployable images.

Running test environments in CI/CD pipelines.

Creating reproducible local development environments.

Serving as the runtime layer before orchestration in Kubernetes or ECS.

Pros

Creates consistent environments across development and production.

Makes application packaging and shipping much simpler.

Works very well in CI/CD and microservice-based architectures.

Has a huge ecosystem and community support.

Cons

Can lead to security issues if images are not hardened properly.

Beginners often misuse containers like virtual machines.

Persistent storage and networking require deeper understanding in production.