docker

Containerizing with Docker involves creating a Dockerfile that specifies your application's dependencies and runtime, then building an image and running it as a container. Write a Dockerfile with FROM, RUN, COPY, and CMD instructions, build it with `docker build -t myapp .`, and run with `docker run myapp`.

Docker Compose defines multi-service applications in a single YAML file, orchestrating containers, networks, and storage together. Write a docker-compose.yml specifying services, volumes, and networks, then use `docker-compose up` to launch the entire stack as interconnected containers.

Optimize Docker builds using multi-stage builds to reduce final image size, leverage layer caching by ordering instructions strategically, use non-root execution for security, and minimize base image bloat. These practices speed builds, reduce attack surface, and improve deployment efficiency.

Docker is language and framework agnostic—it containerizes any application by packaging the runtime, dependencies, and code together. A single Dockerfile pattern works for Node.js, Python, Java, Go, and other languages, enabling consistency across polyglot environments.

Docker integrates into CI/CD by building images during pipeline stages, running tests in containers for isolation, and pushing validated images to registries for deployment. This approach ensures reproducible builds and consistent environments from development through production.

Harden Docker containers by running processes as non-root users, using minimal base images, scanning images for vulnerabilities, applying principle of least privilege to file permissions, and keeping dependencies updated. These reduce attack surface and prevent privilege escalation.