When installing docker, an error message appears (on alicloud server):

Error: Failed to download metadata for repo ‘docker-ce-stable’: Cannot
download repomd.xml: Cannot download repodata/repomd.xml: All mirrors
were triedError: Failed to download metadata for repo
‘docker-ce-stable’: Cannot download repomd.xml: Cannot download
repodata/repomd.xml: All mirrors were tried

Solution:

Here, my work is done on the alicloud server. There are some small problems. According to the alicloud official website, you need to make some minor modifications to your docker-ce.repo

Change the $releasever variable to 7