当虚拟机无法连接访问到外网https://registry-1.docker.io/v2，执行docker pull命令会抛出异常，如下：
[root@localhost default]# docker pull debian
Using default tag: latest
Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
通过设置代理可以解决：
-
创建http-proxy.conf文件:
$ mkdir -p /etc/systemd/system/docker.service.d
$ vim /etc/systemd/system/docker.service.d/http-proxy.conf
添加如下内容：
[Service]
Environment="HTTP_PROXY=http://<allowed_proxy_ipv4_address>:<proxy_port_num>/"
[Service]
Environment="HTTPS_PROXY=https://<allowed_proxy_ipv4_address>:<proxy_port_num>/"
- 执行reload命令: $ sudo systemctl daemon-reload
- 重启docker: $ sudo systemctl restart docker
- 查看环境变量值： $ systemctl show --property=Environment docker
再次执行：
[root@localhost docker.service.d]# docker pull debian
Using default tag: latest
latest: Pulling from library/debian
55cbf04beb70: Pull complete
Digest: sha256:f1f61086ea01a72b30c7287adee8c929e569853de03b7c462a8ac75e0d0224c4
Status: Downloaded newer image for debian:latest