申请免费SSL证书

Let's Encrypt 安装配置教程，免费的 SSL 证书
官网：https://letsencrypt.org/
安装Let's Encrypt安装非常简单直接克隆就可以了

git clone https://github.com/letsencrypt/letsencrypt

生成通配符证书
期间需要根据提示设置DNS TXT记录,用作你对判断你是否拥有域名使用权

cd letsencrypt
./certbot-auto certonly -d *.you.cn --manual --preferred-challenges dns --server https://acme-v02.api.letsencrypt.org/directory

其中"you.cn"换成你的一级域名即可
参数 说明
Certonly 表示安装模式，Certonly有安装模式和验证模式两种类型的插件
--manual 表示手动安装插件，CertBot有很多插件，不同的插件都可以申请证书，用户可以根据需要自行选择
-d 为哪些主机申请证书，如果是通配符，输入*.you.cn(可替换为自己的一级域名)
--preferred-challenges dns 使用DNS方式校验域名所有权
--server Let’s Encrypt ACME v2版本使用的服务器不同于v1版本，需要显示指定
接着可以看到下面界面结果：

Dependency Installed:
dwz.x86_64 0:0.11-3.el7 perl-srpm-macros.noarch 0:1-8.el7 tcl.x86_64 1:8.5.13-8.el7 tix.x86_64 1:8.4.3-12.el7 tk.x86_64 1:8.5.13-6.el7 tkinter.x86_64 0:2.7.5-69.el7_5 
Complete!
Creating virtual environment...
Installing Python packages...
Installation succeeded.
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator manual, Installer None
Enter email address (used for urgent renewal and security notices) (Enter 'c' to
cancel): 123@163.com

接下来需要输入些指令

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Please read the Terms of Service at
https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf. You must
agree in order to register with the ACME server at
https://acme-v02.api.letsencrypt.org/directory
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(A)gree/(C)ancel: A
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Would you be willing to share your email address with the Electronic Frontier
Foundation, a founding partner of the Let's Encrypt project and the non-profit
organization that develops Certbot? We'd like to send you email about our work
encrypting the web, EFF news, campaigns, and ways to support digital freedom.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(Y)es/(N)o: N
Obtaining a new certificate
Performing the following challenges:
dns-01 challenge for kuaichuangkeji.com
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
NOTE: The IP of this machine will be publicly logged as having requested this
certificate. If you're running certbot in manual mode on a machine that is not
your server, please ensure you're okay with that.
Are you OK with your IP being logged?
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(Y)es/(N)o: Y

这里有几个需交互的提示
• 是否同意 Let's Encrypt 协议要求=>需要同意
• 是否分享你的邮箱
• 询问是否对域名和机器（IP）进行绑定=>需要同意
需要注意的地方：

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Please deploy a DNS TXT record under the name
_acme-challenge.you.cn with the following value:
RYtObhDvEcXewZckknNQkBKIkvwIlbb4PNRel74LNwU
Before continuing, verify the record is deployed.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Press Enter to Continue
Waiting for verification...
Cleaning up challenges

要求配置 DNS TXT 记录，从而校验域名所有权，也就是判断证书申请者是否有域名的所有权。
上面输出要求给 _acme-challenge.you.cn 配置一条 TXT 记录，在没有确认 TXT 记录生效之前不要回车执行。
我用的是阿里云的域名服务器，控制台具体操作如下图所示：

确认生效后，回车执行，输出如下

IMPORTANT NOTES:
- Congratulations! Your certificate and chain have been saved at:
/etc/letsencrypt/live/you.cn/fullchain.pem
Your key file has been saved at:
/etc/letsencrypt/live/you.cn/privkey.pem
Your cert will expire on 2019-02-27. To obtain a new or tweaked
version of this certificate in the future, simply run certbot-auto
again. To non-interactively renew *all* of your certificates, run
"certbot-auto renew"
- If you like Certbot, please consider supporting our work by:
Donating to ISRG / Let's Encrypt: https://letsencrypt.org/donate
Donating to EFF: https://eff.org/donate-le

看到这个界面内容的话，恭喜你，证书安装成功了。

证书续签
注:证书在到期前30天才会续签成功,但为了确保证书在运行过程中不过期,官方建议每天自动执行续签两次;
使用crontab自动续期
crontab -e // 编辑定时任务

0 */12 * * * certbot renew --quiet --renew-hook "/etc/init.d/nginx reload"

• 需要注意"/etc/init.d/nginx reload"为nginx重启命令，需要根据自己服务器的重启命令重启即可；这里建议使用reload，不推荐使用restart，因为这样万一配错了，也不会影响服务器其他项目的运行
证书保存的路径[配置nginx需要用到的]
/etc/letsencrypt/live/you.cn/fullchain.pem
/etc/letsencrypt/live/you.cn/privkey.pem
nginx 开启 https
证书生成完成后可以到 /etc/letsencrypt/live/ 目录下查看对应域名的证书文件。编辑 nginx 配置文件监听 443 端口，启用 SSL，并配置 SSL 的公钥、私钥证书路径：

server {
listen 443 ssl;
server_name you.cn;
root /home/www/you;
index index.html index.htm index.php;
ssl on;
ssl_certificate /etc/letsencrypt/live/you.cn/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/you.cn/privkey.pem;
...
}

添加 HTTP 自动跳转到 HTTPS：

server {
listen 80;
server_name you.cn;
location / {
           rewrite ^(.*)$ https://$host$1 permanent;
     }
}

配置好nginx后，重启nginx
证书安装成功后，该域名下的所有二级域名都可以使用噢
取消证书
可以使用一下命令取消刚刚生成的密匙，也就是以上的反操作：

certbot revoke --cert-path /etc/letsencrypt/live/you.cn/cert.pem
certbot delete --cert-name you.cn