错误

alex@ubuntu:~$ sudo apt-get install docker-ce docker-ce-cli containerd.io
[sudo] password for alex: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'moby-containerd' instead of 'containerd.io'
Package docker-ce is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  moby-engine moby-cli docker-ce-cli:arm64

E: Package 'docker-ce' has no installation candidate
E: Unable to locate package docker-ce-cli

解决方法：添加阿里镜像源

sudo add-apt-repository "deb [arch=amd64] http://mirrors.aliyun.com/docker-ce/linux/ubuntu $(lsb_release -cs) stable"

参考 ubuntu 16.04 安装docker (阿里云镜像)