实验环境：CentOS Linux release 7.3.1611 (Core)
内核版本：Linux version 3.10.0-514.el7.x86_64
Nginx版本： Nginx-1.13.0

Let’s Encrypt是一个免费的、自动化、开放的证书颁发机构。由Mozilla、Cisco、Chrome、facebook、Akamai等众多公司和机构发起的，其安全稳定及其可靠。具体信息可以去letsencrypt官方网站了解详情。

今天我们就充分利用Lets Encrypt让你的网站实现https加密。

官网：//letsencrypt.org/

1.安装certbot及源扩展包

$ yum install -y epel-release

Certbot是Let’s Encrypt官方指定推荐的客户端。通过 Certbot，你可以自动化部署 Let’s Encrypt SSL证书，以便为网站加上HTTPS加密支持。

$ yum install certbot
$ certbot certonly

Saving debug log to /var/log/letsencrypt/letsencrypt.log
How would you like to authenticate with the ACME CA?
//你是希望如何使用ACME CA进行身份验证？
-------------------------------------------------------------------------------
1: Place files in webroot directory (webroot)
//将文件放在webroot目录
2: Spin up a temporary webserver (standalone)
//使用临时Web服务器（独立目录）
-------------------------------------------------------------------------------
Select the appropriate number [1-2] then [enter] (press 'c' to cancel):1 【选择1回车】
Enter email address (used for urgent renewal and security notices) (Enter 'c' to
cancel):su@renwole.com【输入您的邮箱地址，用于紧急更新和安全通知】

Starting new HTTPS connection (1): acme-v01.api.letsencrypt.org
-------------------------------------------------------------------------------
Please read the Terms of Service at
//letsencrypt.org/documents/LE-SA-v1.1.1-August-1-2016.pdf. You must agree
in order to register with the ACME server at
//acme-v01.api.letsencrypt.org/directory
-------------------------------------------------------------------------------
(A)gree/(C)ancel: A【选择A回车同意服务条款，C为拒绝】
-------------------------------------------------------------------------------
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 EFF and
our work to encrypt the web, protect its users and defend digital rights.
-------------------------------------------------------------------------------
(Y)es/(N)o:Y【您是否愿意分享您的电子邮件地址，建议选择Y回车】
Please enter in your domain name(s) (comma and/or space separated) (Enter 'c'
to cancel): blog.renwole.com【输入域名回车】
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for blog.renwole.com
Select the webroot for blog.renwole.com:
-------------------------------------------------------------------------------
1: Enter a new webroot
//输入网站绝对路径
-------------------------------------------------------------------------------
Press 1 [enter] to confirm the selection (press 'c' to cancel):1【选择数字1回车】
Input the webroot for blog.renwole.com: (Enter 'c' to cancel):/home/www/blog.renwole.com【输入网站所在绝对路径回车】
Waiting for verification...
Waiting for verification...
Cleaning up challenges
Generating key (2048 bits): /etc/letsencrypt/keys/0001_key-certbot.pem
Creating CSR: /etc/letsencrypt/csr/0001_csr-certbot.pem

IMPORTANT NOTES:
- Congratulations! Your certificate and chain have been saved at
/etc/letsencrypt/live/blog.renwole.com/fullchain.pem. Your cert
will expire on 2017-08-09. To obtain a new or tweaked version of
this certificate in the future, simply run certbot again. To
non-interactively renew *all* of your certificates, run "certbot
renew"
- If you like Certbot, please consider supporting our work by:

Donating to ISRG / Let's Encrypt: //letsencrypt.org/donate
Donating to EFF:

恭喜!您的SSL证书和密钥链接已保存，你的证书将于2017-08-09到期。

注意：这里需要说明，在生成证书之前，你必须保证nginx 443端口是运行状态，否则会生成证书失败。

2.自动续订

Certbot可以配置为在证书过期之前自动更新证书。由于Let’s Encrypt SSL证书有效期时间为90天，所以建议您利用此功能。您可以通过运行以下命令来测试证书的自动续订：

$ sudo certbot --nginx certonly

如果以上正常工作，你可以通过添加运行以下操作的cron或systemd定时任务安排自动更新：

certbot renew

我们写一个自动执行脚本，建议每小时执行一次：

$ sudo crontab -e

添加以下内容：

0 */6 * * * /usr/bin/certbot renew --quiet && /bin/systemctl restart nginx

保存并退出！

通过命令查看是否添加成功：

$ crontab -l
0 */6 * * * /usr/bin/certbot renew --quiet && /bin/systemctl restart nginx

重启crontab

$ systemctl status crond.service
$ systemctl restart crond.service

通过命令观察 crontab 是否执行：

$ tail -f /var/log/cron

证书是否续订成功，可以通过以下命令管理查看证书信息：

$ certbot certificates

更多Certbot命令请参阅官方文档 //certbot.eff.org/docs/

3.配置nginx.conf
接下来修改Nginx配置文件，修改sever段，去掉相应注释，将生成的SSL证书填写到ssl_certificate后面，将生成的密钥填写到ssl_certificate_key后面，保存并重启nginx服务器即可。

# vi /usr/local/nginx/conf/nginx.conf

server {
 listen 443 ssl;

 ssl_certificate /etc/letsencrypt/live/blog.renwole.com/fullchain.pem;
 ssl_certificate_key /etc/letsencrypt/live/blog.renwole.com/privkey.pem;

# ssl_session_cache shared:SSL:1m;
 ssl_session_timeout 5m;

# ssl_ciphers HIGH:!aNULL:!MD5;
 ssl_prefer_server_ciphers on;

# location / {
 # root html;
 # index index.html index.htm;
 # }
 }

使用谷歌浏览器访问//blog.renwole.com/可以看到绿色的安全小锁图标，说明网站已经https加密成功。