What happens when the docker image disappears?

With the further development of DevOps and the popularity of cloud native applications, Docker has become one of the standard tools for development, deployment and operation and maintenance. Docker is a tool that directly operates containers, and containers provide a lightweight virtualization method that can package code, environment and dependencies into an independent running environment, and quickly transplant and deploy it on different nodes to maximize It greatly improves the portability and scalability of applications, making operation and maintenance more convenient and efficient.

However, in the actual use of Docker, sometimes you encounter some strange problems, such as the image missing. This problem is generally caused by an image on Docker Hub being deleted or the registry where it is located inaccessible, causing Docker to make an error during the process of pulling the image, thus affecting the stability and reliability of the entire application.

So, how to solve this problem? Generally speaking, there are two solutions: one is to use other image sources, such as Alibaba Cloud, Tencent Cloud, etc.; the other is to build Docker Registry locally and save the required images locally, thereby no longer relying on external sources. The mirror source improves the reliability and stability of the application.

Use other image sources

Taking Alibaba Cloud as an example, we need to first register an account on Alibaba Cloud's container image service and activate the service. Select "Image Accelerator" on the console, and you will get a URL. This URL is the Docker image accelerator address provided by Alibaba Cloud.

Copy this address to the /etc/docker/daemon.json file and restart the Docker service. For example:

{
  "registry-mirrors": ["https://xxxxxxxx.mirror.aliyuncs.com"]
}

When you use the Docker command to pull the image later, you can add the --registry-mirror parameter after the command to specify the use of Alibaba Cloud Mirror Accelerator, for example:

docker pull --registry-mirror=https://xxxxxxxx.mirror.aliyuncs.com library/nginx

Building Docker Registry locally

Using domestic Docker Hub image sources such as Alibaba Cloud and Tencent Cloud can help solve the problem of missing images, but the operating model of these companies generally charges based on volume. For some businesses that need to use resources very frequently, they may also face higher cost pressure. Moreover, the country has also begun to require some important data to be stored and transmitted within China. Therefore, at some point, the unavailability of foreign registry ports may also become a bottleneck.

Building Docker Registry locally can solve these problems. We only need to build a Docker Registry on a Linux server and push the required image to this Registry. The specific steps are as follows:

1. Pull the Docker Registry image

Use the following command on the local server to pull the Docker Registry image:

docker pull registry

2. Run the Docker Registry container

Use the following command to start the Docker Registry container:

docker run -d -p 5000:5000 --restart=always --name registry registry:latest

By default, the Registry will listen on the local port 5000 and use the local file system as image storage library.

3. Push the image

Use the following command on the local computer to push a local Dcoker image to the Registry:

docker tag <local_image_name> <registry_url>/<remote_image_name>
docker push <registry_url>/<remote_image_name></remote_image_name></registry_url></remote_image_name></registry_url></local_image_name>

where is the local Docker image name, <registry_url></registry_url> is the IP address of our local server and the 5000 port number, <remote_image_name></remote_image_name> is The name of the image pushed to the Registry.

4. Pull the image

Use the following command to pull the image from the Registry:

docker pull <registry_url>/<remote_image_name></remote_image_name></registry_url>

By building the Docker Registry locally, we can quickly save and retrieve it required images, and better control the deployment and operation of Docker images. Moreover, the locally built Docker Registry can support more advanced functions, such as image management, account permission control, image warehouse modeling, image sharing, etc. These functions can further optimize our Docker operation and maintenance process and improve our performance in DevOps. Competitiveness.

In short, the problem of missing images is a common and troublesome problem during Docker operation. However, through reliable Docker image accelerators such as Alibaba Cloud or building Docker Registry locally, we can solve this problem well. This further improves the reliability and stability of applications, speeds up construction and deployment, and improves the efficiency of DevOps.

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