阿里云Ubuntu 14.04 + Nginx + let's encrypt 搭建https访问

参考页面：

1. 下载let's encrypt

$ sudo add-apt-repository ppa:certbot/certbot
$ sudo apt-get update
$ sudo apt-get install certbot

　　无法找到add-apt-repository时，需要

apt-get install python-software-properties
apt-get install software-properties-common

2. 生成密钥

certbot certonly --standalone -d example.com -d www.example.com

执行成功会显示如下内容：

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at
   /etc/letsencrypt/live/【这里是你的域名】/fullchain.pem. Your cert will
   expire on 【这里是到期时间】. 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

　　红色内容在下一步会被使用。

3. 配置nginx

listen 443 ssl;
ssl_certificate /etc/letsencrypt/live/【这里是你的域名】/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/【这里是你的域名】/privkey.pem;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_prefer_server_ciphers on;
ssl_ciphers AES256+EECDH:AES256+EDH:!aNULL;
listen [::]:443 ssl ipv6only=on;

　　请注意这里的两个红色路径所对应的文件不相同。

4. 重启nginx

1	`nginx -s reload`

　　这时通过https访问网站，访问成功。

　　通过http访问网站，失败。错误：ERR_CONNECTION_REFUSED

5. 重定向http访问到https

server {
        listen 80;
        server_name 【这里是你的域名】;
        rewrite ^(.*) https://$server_name$1 permanent;
}

　　再次访问http，成功。　　

至此，配置完成。如下图

* let's encrypt 只有90天的期限，续期使用如下代码：

1	`certbot renew --dry-run <br>certbot renew`

　此操作前，请先关闭nginx

nginx -s stop

　重启nginx，可能会遇到 [error] open() "/run/nginx.pid" failed (2: No such file or directory) 这样的问题，解决方法如下（参考自：http://blog.csdn.net/llnara/article/details/8691049）：