proxy with upstream connections keepalive

gistfile1.txt

worker_processes auto;
worker_rlimit_nofile 65535;

error_log    /certs/error.log debug;

events {
    worker_connections 15000;
    multi_accept on;
    use epoll;
}

http {
    resolver 8.8.8.8;

    keepalive_requests 100000;
    tcp_nopush on;
    tcp_nodelay off;

    upstream backend {
        server 46.174.180.163;
        keepalive 100;
    }

    server {
        server_name bilet.intercity.pl;
        listen 443 ssl reuseport backlog=10000 fastopen=256;

        access_log    /certs/access.log;

        ssl_certificate /certs/nginx.crt;
        ssl_certificate_key /certs//nginx.key;
        add_header Strict-Transport-Security "max-age=31536000";
        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers "EECDH+ECDSA+AESGCM EECDH+aRSA+AESGCM EECDH+ECDSA+SHA384 EECDH+ECDSA+SHA256 EECDH+aRSA+SHA384 EECDH+aRSA+SHA256 EECDH+aRSA+RC4 EECDH EDH+aRSA HIGH !RC4 !aNULL !eNULL !LOW !3DES !MD5 !EXP !PSK !SRP !DSS";
        server_tokens off;

        location / {
            proxy_ssl_session_reuse on;
            proxy_pass https://backend;
            proxy_http_version 1.1;
            proxy_redirect off;
            proxy_set_header X-Forwarded-Host $host;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_set_header Connection "";
        }
    }
}