阿里云服务器执行yum，一直下载docker-ce-stable失败

~# yum update
Docker CE Stable - x86_64                               0.0  B/s |   0  B     02:00    
Errors during downloading metadata for repository 'docker-ce-stable':
  - Curl error (28): Timeout was reached for https://download.docker.com/linux/centos/8/x86_64/stable/repodata/repomd.xml [Connection timed out after 30000 milliseconds]
Error: Failed to download metadata for repo 'docker-ce-stable': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried

这可能是由于YUM配置文件中包含了Docker仓库的配置，或者您的yum源中包含了Docker的相关依赖。您可以尝试以下步骤解决问题：

1. 查看YUM配置： 查看 `/etc/yum.repos.d/` 目录下是否有与Docker相关的repo文件，如`docker.repo`或`docker-ce.repo`，并临时移除或注释掉相关配置。

本人通过查看`/etc/yum.repos.d/` 目录，发现有docker-ce.repo，打开

[docker-ce-stable]
name=Docker CE Stable - $basearch
baseurl=https://download.docker.com/linux/centos/$releasever/$basearch/stable
enabled=1
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-stable-debuginfo]
name=Docker CE Stable - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/$releasever/debug-$basearch/stable
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-stable-source]
name=Docker CE Stable - Sources
baseurl=https://download.docker.com/linux/centos/$releasever/source/stable
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-test]
name=Docker CE Test - $basearch
baseurl=https://download.docker.com/linux/centos/$releasever/$basearch/test
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-test-debuginfo]
name=Docker CE Test - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/$releasever/debug-$basearch/test
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-test-source]
name=Docker CE Test - Sources
baseurl=https://download.docker.com/linux/centos/$releasever/source/test
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-nightly]
name=Docker CE Nightly - $basearch
baseurl=https://download.docker.com/linux/centos/$releasever/$basearch/nightly
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-nightly-debuginfo]
name=Docker CE Nightly - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/$releasever/debug-$basearch/nightly
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
[docker-ce-nightly-source]
name=Docker CE Nightly - Sources
baseurl=https://download.docker.com/linux/centos/$releasever/source/nightly
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

发现第4行，enabled=1，其他都是0，将其改为0，解决

2. 临时禁用Docker源： 在执行yum命令时，可以使用`--disablerepo=docker*`参数来临时忽略Docker仓库。