安裝 snap 

sudo apt update
sudo apt install snapd

安裝 Certbot

sudo snap install --classic certbot

連結檔案，方便使用命令

sudo ln -s /snap/bin/certbot /usr/bin/certbot

因為這裡使用的是Cloudflare解析，這裡直接安裝Cloudflare外掛，

若支援的外掛沒有的DNS服務商，請自行移步這裡檢視獲取證書的方法

https://certbot.eff.org/instructions?ws=nginx&os=debianbuster

sudo snap install certbot-dns-cloudflare

若出現以下錯誤，則執行根據提示snap set certbot trust-plugin-with-root=ok即可

error: cannot perform the following tasks:
- Run hook prepare-plug-plugin of snap "certbot" (run hook "prepare-plug-plugin": 
-----
Only connect this interface if you trust the plugin author to have root on the system.
Run `snap set certbot trust-plugin-with-root=ok` to acknowledge this and then run this command again to perform the connection.
If that doesn't work, you may need to remove all certbot-dns-* plugins from the system, then try installing the certbot snap again.
-----)

配置外掛所需的Cloudflare帳戶裡的API Key，建立一個檔案（假設放在/etc/cloudflare.ini），內容如下

dns_cloudflare_api_token = your api key

獲取證書

certbot certonly \
  --dns-cloudflare \
  --dns-cloudflare-credentials /etc/cloudflare.ini \
  -d domainname.com \
  -d *.domainname.com

如果沒有意外，將返回獲取成功的資訊，自行檢視證書存放的位置，在去配置Nginx即可