[VWWHFSfQ]

My NGINX webserver configuration on AWS behind an ALB is:

/etc/sysctl.conf:

    net.core.wmem_max = 12582912
    net.core.rmem_max = 12582912
    net.ipv4.tcp_rmem = 10240 87380 12582912
    net.ipv4.tcp_wmem = 10240 87380 12582912
    fs.file-max = 1000000
    net.ipv4.ip_local_port_range = 1024 65535
    net.ipv4.tcp_tw_recycle = 1
    net.ipv4.tcp_tw_reuse = 1
    net.ipv4.tcp_max_syn_backlog = 262144
    net.ipv4.tcp_syncookies = 0
    net.ipv4.tcp_fin_timeout = 3
    net.ipv4.tcp_syn_retries = 2
    net.ipv4.tcp_synack_retries = 2
    net.ipv4.tcp_no_metrics_save = 1
    net.ipv4.tcp_max_orphans = 262144
    net.core.somaxconn = 1000000

nginx.conf (just the relevant directives):

    worker_rlimit_nofile 102400;

    events {
      worker_connections 102400;
      multi_accept on;
    }

    http {
        server {
          listen 80 default_server reuseport backlog=102400;
          ...
        }    
    }

As you can see, the socket and backlog-related values have been cranked way up. I've never had any problems with this configuration. Because these servers are behind and ALB I don't know how relevant they are since the SYN and SYN-ACK relation to RTT is between the server and the load balancer, not the remote clients. But I could be wrong. Maybe there's something I'm missing. But I've never had a problem, and I've never had any performance problems related to TCP connections in the kernel or NGINX.

[shanemhansen]

I think for ALB you'll see pooled connections (http or http2) so I would expect the number of TCP connections to stay pretty low. In http2 it could theoretically be as low as one.