安装Certbot SSL证书后Nginx 443端口拒绝HTTPS连接求助

环境信息 #

• 系统：运行Debian的树莓派
• Nginx版本：1.14.2
• Certbot版本：1.31.0
• 已通过sudo certbot --nginx命令成功安装SSL证书

Nginx配置文件（/etc/nginx/sites-available/default） #

upstream loadbalancer {
  least_conn;
  server localhost:3500;
  server localhost:3501;
  server localhost:3502;
  server localhost:3503;
}

server {
        index index.html index.htm index.nginx-debian.html;
        server_name www.example.com;

        # react app & front-end files
        location / {        
                root /home/pi/apps/network/build;
                try_files $uri /index.html;
        }

        location /api/ {        
                proxy_pass http://loadbalancer/;
                proxy_buffering off;
                proxy_cache off;
                proxy_set_header Host $host;
                proxy_set_header Connection '';
                proxy_http_version 1.1;
                chunked_transfer_encoding off;
        }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/www.example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/www.example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}

server {
    if ($host = www.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    server_name www.example.com;
    listen 80;
    return 404; # managed by Certbot
}

已做排查 #

• 此前HTTP协议访问一切正常，切换HTTPS后出现ERR_CONNECTION_REFUSED错误
• 证书生成过程无异常，初步排除证书本身问题
• 执行端口监听检查命令sudo netstat -plnt | grep ":80\|:443"，结果显示两个端口均处于监听状态：

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      8743/nginx: master
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      8743/nginx: master

• 当前未启用防火墙，排除本地防火墙拦截端口的可能

求助需求 #

希望有人能指出问题所在或提供进一步的排查思路。

内容的提问来源于stack exchange，提问作者veka