Docker Images: Application Blueprints

Docker images are the foundational blueprints for applications in the Docker ecosystem. An image is a read-only template that contains everything needed to run a piece of software, including:

• Code;
• Runtime;
• Libraries;
• Environment variables;
• Configuration files.

Images are designed to be portable and consistent, ensuring that your application runs the same way regardless of where the image is deployed. You can think of a Docker image as a snapshot or recipe that describes how to set up and configure an application environment.

What Is a Docker Container?

While images define what an application should look like, containers are the actual running instances of those images. A Docker container is a lightweight, standalone, and executable package that encapsulates both the application and its dependencies.

When you start a container, Docker creates a writable layer on top of the image, allowing the container to maintain its own state and changes during its lifecycle.

Key points about container lifecycle:

• Creation: You create a new container from an image;
• Running: The container executes your application as an isolated process;
• Stopping: You can stop a running container at any time;
• Restarting: Containers can be restarted as needed;
• Removal: Once you remove a container, it is deleted from your system.

Any changes made within a container are lost when it is stopped or deleted, unless you save those changes externally or commit them to a new image. This ensures containers remain clean, consistent, and easily reproducible.