Understanding Images and Containers
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.
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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.
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