Shulou(Shulou.com)06/02 Report--

1. Docker image

The docker image is similar to the image of a virtual machine, similar to the windows system on which we install the system, some systems are pure (only basic os), some are clones (software is installed on os, such as: qq, etc.). But he is static and read-only.

Mirroring is the basis for creating docker containers.

Mirrors are tiered storage

Mirroring consists of multiple layers of file system federation (we can fully understand this concept by creating mirrors in pull)

When the image is built, it is built layer by layer, and the former layer is the foundation of the latter layer. After each layer is built, there will be no change, and any change on the latter layer will only happen at your own level. For example, deleting a file in the previous layer does not actually delete the file in the previous layer, but only marks the file as deleted at the current layer. Although the file will not be seen when the final container runs, it will actually follow the image all the time. Therefore, when building the image, you need to be extra careful, each layer contains only what needs to be added by that layer, and any extra stuff should be cleaned up before the end of the layer construction.

2. Docker container

A container is an instance that runs from an application created in an image. It can start, start, stop, delete, and these containers are isolated and invisible from each other. When the container starts from the mirror, a writable layer (storage layer) is created at the top of the mirror.

The life cycle of the container storage layer is the same as that of the container. When the container dies, the container storage layer also dies. Therefore, any information saved in the container storage layer is lost when the container is deleted.

The container should not write any data to its storage tier, and the container storage tier should remain stateless. All file writing operations should use data volumes (Volume) or bind host directories. Reads and writes at these locations will skip the container storage layer and read and write directly to the host (or network storage), resulting in higher performance and stability.

The life cycle of the data volume is independent of the container, the container dies, and the data volume does not die. Therefore, after using the data volume, the data is not lost after the container is deleted or rerun.

To put it simply, the container is a sandboxie running in the mirror image.

3. Docker warehouse

The docker repository is similar to the code repository and is the central place for docker to store image files. After we have built the image, we can upload it to the repository by push, and we can use it directly by pull next time.

Docker can be divided into open warehouses (public), and the official warehouse is docker HUB (https://hub.docker.com). Some domestic cloud service providers provide Docker Hub mirroring services (Registry Mirror), which are called accelerators. Common are Aliyun Accelerator (https://ddddsl2r.mirror.aliyuncs.com), DaoCloud Accelerator (https://www.daocloud.io/mirror#accelerator-doc) and so on. Another category is private repositories, where users can also build private Docker Registry locally. Docker officially provides Docker Registry image, which can be used directly as a private Registry service. In addition, in addition to the official Docker Registry, there are third-party software that implements Docker Registry API, and even provides a user interface and some advanced features. For example, VMWare Harbor and Sonatype Nexus.

The warehouse registration server (registry) is the place where the warehouse is stored, and there are often multiple warehouses on it. A certain type of image is stored in each warehouse, and multiple images are usually distinguished by different tag. We can specify which version of the software is mirrored by the format of:. If no label is given, latest will be used as the default label.

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