使用Let's Encrypt免费证书实现https
Let's Encrypt是一家免费、开放、自动化的证书颁发机构（CA），为公众的利益而运行（由非盈利组织互联网安全研究小组（ISRG）运营）。
前提：你需要有自己的域名
生成证书的方式有很多种，详情点击这里。
我这里以Certbot来生成证书。
（1）、选择证书服务对象和操作系统
选择完后下拉就会出现具体的操作步骤，如下：
（2）、安装epel源
yum install epel-release -y其他操作系统及其安装方法可以点这里。
（3）、安装certbot
yum install certbot python2-certbot-nginx（4）、生成证书
可以选择两种方式。
第一种，直接生成证书并配置NGINX。
certbot --nginx第二种，只生成证书，NGINX需要自己配置
certbot certonly --nginx我选择的第二种，输出详情如下：
[root@VM_0_2_centos ssl]# certbot certonly --nginxSaving debug log to /var/log/letsencrypt/letsencrypt.logPlugins selected: Authenticator nginx, Installer nginxEnter email address (used for urgent renewal and security notices) (Enter 'c' tocancel): coolops@163.comStarting new HTTPS connection (1): acme-v02.api.letsencrypt.org- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Please read the Terms of Service athttps://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf. You mustagree in order to register with the ACME server athttps://acme-v02.api.letsencrypt.org/directory- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -(A)gree/(C)ancel: A- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Would you be willing to share your email address with the Electronic FrontierFoundation, a founding partner of the Let's Encrypt project and the non-profitorganization that develops Certbot? We'd like to send you email about our workencrypting the web, EFF news, campaigns, and ways to support digital freedom.- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -(Y)es/(N)o: YStarting new HTTPS connection (1): supporters.eff.orgWhich names would you like to activate HTTPS for?- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -1: jenkins.coolops.cn2: www.coolops.cn- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Select the appropriate numbers separated by commas and/or spaces, or leave inputblank to select all options shown (Enter 'c' to cancel): 1Obtaining a new certificatePerforming the following challenges:http-01 challenge for jenkins.coolops.cnWaiting for verification...Cleaning up challengesIMPORTANT NOTES: - Congratulations! Your certificate and chain have been saved at: /etc/letsencrypt/live/jenkins.coolops.cn/fullchain.pem Your key file has been saved at: /etc/letsencrypt/live/jenkins.coolops.cn/privkey.pem Your cert will expire on 2020-08-23. 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" - Your account credentials have been saved in your Certbot configuration directory at /etc/letsencrypt. You should make a secure backup of this folder now. This configuration directory will also contain certificates and private keys obtained by Certbot so making regular backups of this folder is ideal. - 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安装步骤执行即可，当看到如上输出信息，则表明证书签发成功。
我们可以到相应的目录下查看证书
[root@VM_0_2_centos jenkins.coolops.cn]# cd /etc/letsencrypt/live/jenkins.coolops.cn[root@VM_0_2_centos jenkins.coolops.cn]# ll total 4lrwxrwxrwx 1 root root 42 May 25 14:50 cert.pem -> ../../archive/jenkins.coolops.cn/cert1.pemlrwxrwxrwx 1 root root 43 May 25 14:50 chain.pem -> ../../archive/jenkins.coolops.cn/chain1.pemlrwxrwxrwx 1 root root 47 May 25 14:50 fullchain.pem -> ../../archive/jenkins.coolops.cn/fullchain1.pemlrwxrwxrwx 1 root root 45 May 25 14:50 privkey.pem -> ../../archive/jenkins.coolops.cn/privkey1.pem-rw-r--r-- 1 root root 692 May 25 14:50 README注意：证书是有过期时间的，默认是3个月，我们可以使用脚本自动续约（见后文）。
（5）、配置NGINX
server{ listen 80 ; listen 443 ssl; server_name jenkins.coolops.cn; ssl_certificate /etc/letsencrypt/live/jenkins.coolops.cn/fullchain.pem; ssl_certificate_key /etc/letsencrypt/live/jenkins.coolops.cn/privkey.pem; ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:HIGH:!aNULL:!MD5:!RC4:!DHE; ssl_prefer_server_ciphers on; ssl_session_cache shared:SSL:1m; ssl_session_timeout 5m; location / { proxy_connect_timeout 180; proxy_send_timeout 180; proxy_read_timeout 180; proxy_set_header Host $host; proxy_set_header X-Forwarder-For $remote_addr; proxy_pass http://127.0.0.1:8080; } }然后浏览器访问，并查看证书信息如下：
（6）、配置证书自动续签
官方已经提供了，直接加入cron即可。
echo "0 0,12 * * * root python -c 'import random; import time; time.sleep(random.random() * 3600)' && certbot renew -q" | sudo tee -a /etc/crontab > /dev/null完