Docker in Practice: Images, Containers, and Orchestration

Docker helps you package an application and its dependencies as an image. An image is a portable blueprint that can be shared. A container is a running instance of that image, with its own writable layer, network, and process space. This makes applications more predictable across different machines.

Images are built in layers. Each command in a Dockerfile adds a layer. Layers help with caching: if you change one part, Docker rebuilds only what is needed. This keeps builds fast and repeatable. Small, focused images also start quicker and use less disk space.

Getting started is simple. Pull a small image, start a container, and stop it when you are done. Here are practical steps you can try, using plain commands:

  • Pull an image: docker pull alpine:3.18
  • Run a container interactively: docker run -it –rm alpine:3.18 sh
  • See all containers: docker ps -a
  • Save changes as a new image: docker commit myname/myimage
  • Publish locally or to a registry: docker push myname/myimage

As soon as you have a running container, you can do more. Mount a folder from your device as a volume to store data, and map ports to access services from your computer. For example, you could run a tiny web server and then visit it in a browser. With practice, you will create small, reusable image recipes and compose them into larger apps.

Orchestration helps you manage many containers across one or more hosts. Docker Compose is a friendly start for multi-container apps, using a single file to describe services, networks, and volumes. For larger needs, Kubernetes offers scaling, rolling updates, and self-healing containers. Start with Compose for local projects, then explore Kubernetes when your needs grow. This path keeps things simple while you learn how containers fit into real workflows.

Key Takeaways

  • Images are blueprints; containers are their running instances.
  • Use volumes and port mappings to keep data safe and services accessible.
  • Start with Docker Compose for multi-service apps, then look to larger orchestration when needed.