nginx proxy_pass 502 这是什么错误？

配置

    server {
        listen       443 ssl;
        server_name  192.168.1.17;
 
        ssl_certificate cert/2737432_run.csmp.cloud.pem;
        ssl_certificate_key  cert/2737432_run.csmp.cloud.key;
 
        ssl_session_cache    shared:SSL:1m;
        ssl_session_timeout  5m;
 
        ssl_ciphers  HIGH:!aNULL:!MD5;
        ssl_prefer_server_ciphers  on;
 
        location / {
            proxy_pass  https://114.247.220.12:8839;
        }
    }

报错信息

2020/07/22 17:54:29 [crit] 358452#359832: *112 SSL_do_handshake() failed (SSL: error:141A318A:SSL routines:tls_process_ske_dhe:dh key too small) 

while SSL handshaking to upstream, client: 192.168.15.55, server: 192.168.15.55, request: "GET /favicon.ico HTTP/1.1", upstream: "https://114.113.112.35:6443/favicon.ico", 
host: "192.168.15.55:8839", referrer: "https://192.168.15.55:8839/"

这是什么错误？