Docker Images and Dockerfile

Images

A Docker image is a snapshot of a file and operating system with libraries and application executables. In essence, an image is a recipe or template for creating a container. It’s similar to how some computer languages let you define a reusable class template for instantiating objects of the same type.

Any number of containers can be started from a single image. This permits scaling on production servers, although you’re unlikely to launch multiple containers from the same image during development.

The Docker Hub provides a repository of commonly-used images for:

• dependencies such as NGINX, MySQL, MongoDB, Elasticsearch, Redis, etc.
• language runtimes or frameworks such as Node.js, PHP, Python, Ruby, Rust), and any other language you’ve heard of.
• applications such as WordPress, Drupal, Joomla, Nextcloud, etc. These often require additional containers such as databases.

🔔 Reminder: Sign-up for a Docker Hub account if you’d like to publish your own images.

Dockerfile

An image is configured using a Dockerfile. It typically defines: