Where to put the image in docker

Docker is an advanced containerization technology that provides a lightweight and flexible way to package, deploy and manage applications. The core components of Docker include Docker engine, Docker Registry and Docker Hub, etc. Among them, Docker Hub is the most popular Docker Registry, which provides a public Docker image repository for global developers to share and use Docker images. But in actual applications, where is the Docker image placed? Next, I will introduce in detail how and where the image in Docker is stored.

1. What is a Docker image

Before understanding where the image in Docker is placed, we need to first understand what a Docker image is. Simply put, a Docker image is a read-only template that contains all the files and configurations used to create a Docker container. These include operating systems, applications, dependent libraries, etc. Because Docker images contain only necessary components, it is a lightweight and portable application packaging and delivery solution.

2. Image storage method in Docker

In Docker, image is a read-only file system. When Docker builds a new image, it packages the contents of the container's file system into an image and saves it to the Docker host's local storage. In other words, a Docker image is composed of layers in the file system. Each layer is read-only and packaged and stored in the system in the Docker image format.

Docker uses a file system called Aufs to store Docker images. In earlier versions of Docker, Docker used OverlayFS to store images. However, due to issues such as OverlayFS not supporting caching during the Docker build process and not providing enough coverage layers, Docker began to use Aufs in version 1.10, making Docker's image storage method more efficient and stable.

3. Image location in Docker

Docker stores the image in the file system of the host. In Linux systems, Docker images are stored in the /var/lib/docker directory by default. In this directory, Docker stores image groups in different folders. Among them, the metadata and information of the Docker image are stored in the /var/lib/docker/image directory. The image data is stored in the /var/lib/docker/aufs/diff directory. The subdirectories in this directory are composed of image layers.

/var/lib/docker/overlay2 directory is the storage location of Docker OverlayFS. If the Docker version is lower than 1.13, the storage location is the /var/lib/docker/overlay directory. In this storage location, Docker stores information and metadata for the middle layers of the hybrid file system.

By default, Docker uses the /var/lib/docker directory to store image and container data. However, if you want to store the Docker image in a different location, you can also change that by changing Docker's configuration file. The drive letter and directory path can be set in the Docker configuration file, allowing you to store the image to a specified disk and location.

Summary

The image in Docker is an important component that is used to package and deliver applications. Docker stores the image in the host's file system, and stores the image layers in different directories through the Aufs file system. By default, Docker images are stored in the /var/lib/docker directory. If you need to change the storage location, you can do so by changing the Docker configuration file. This flexibility and customizability make Docker the containerization technology of choice for developers and operators.

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