Docker containers package applications with all their dependencies into portable, reproducible units. This eliminates the classic "it works on my machine" problem and creates consistency between development, testing, and production environments.
Building and Running Your First Container
A Dockerfile defines the steps to build a container image. Start with a base image, copy your application code, install dependencies, and specify the entry point. The layered filesystem means unchanged layers are cached, making subsequent builds fast.
Docker Compose simplifies multi-container applications by defining services, networks, and volumes in a single YAML file. A typical web application might include containers for the app server, database, and cache, all orchestrated with a single docker-compose up command.
Volume mounts enable live code reloading during development, mapping your local source directory into the container. Combined with port forwarding, you get the isolation benefits of containers without sacrificing the rapid feedback loop developers need.