Complete steps for Docker to pull images

1. Docker pull pulls the image

When using $ docker pull {IMAGE_NAME} to pull an image, there are two situations:

• IMAGE_NAME has a domain name before the first slash

Docker will recognize IMAGE_NAME as an image with a domain name. For example, myregistry.io/space1/image1:latest, Docker will go to the server pointed to by myregistry.io to request the image data. A Docker image is divided into many layers. If the layer exists locally, it will not be pulled again.

• There is no domain name before the first slash in IMAGE_NAME

Docker will concatenate IMAGE_NAME to docker.io/IMAGE_NAME to request the image data. In fact, $ docker pull docker.io/shaowenchen/images1 is equivalent to $ docker pull shaowenchen/images1. For the images provided by DockerHub, the access speed in China is slow, which can be accelerated by adding image sources.

When pulling images, there may be two problems:

1. Pull the non-public image and prompt to log in

Simply log in using docker login. In a non-interactive scenario, you can execute:

$ echo "$DOCKER_PASSWORD" | docker login $REGISTRY -u "$DOCKER_USERNAME" --password-stdin

2. Mirror repository certificate error

If the image repository server is specified in IMAGE_NAME, but the server does not provide a valid https service, the following configuration is required:

In the /etc/docker/daemon.json file, add:

{
 "insecure-registries": ["core.harbor.chenshaowen.com:5000"]
}

Restart Docker for the changes to take effect.

2. Modify the image source to speed up image pulling

• Modify the Docker configuration file daemon.json

In the /etc/docker/daemon.json file, add the mirror source

{ 
 "registry-mirrors": ["https://docker.mirrors.ustc.edu.cn"] 
}

• Modify Docker's systemd parameters

Edit the file /usr/lib/systemd/system/docker.service and add the registry-mirror parameter to the line containing ExecStart.

ExecStart=... --registry-mirror=https://docker.mirrors.ustc.edu.cn

Restart Docker for the changes to take effect.

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