Dockerfile File — Docker Container Definition

Dockerfiles are text files containing instructions for building Docker container images. Each instruction (FROM, RUN, COPY, ENV, EXPOSE, CMD, ENTRYPOINT, etc.) creates a layer in the resulting image. Dockerfiles start with a FROM instruction specifying the base image, followed by commands that install dependencies, copy application code, configure the environment, and define the default command to run. Multi-stage builds allow using multiple FROM instructions to create intermediate build stages, producing smaller final images by copying only necessary artifacts from build stages. Dockerfiles support build arguments (ARG), environment variables (ENV), health checks, volume definitions, and label metadata. Best practices include minimizing layers, using .dockerignore to exclude unnecessary files, running as non-root users, leveraging build cache through instruction ordering, and using specific base image tags. Dockerfiles are fundamental to containerized application development and deployment, enabling reproducible builds across development, CI/CD, and production environments. The format is used by Docker, Podman, BuildKit, and other container runtimes that implement the OCI (Open Container Initiative) image specification.