My config btw:

user imail;
worker_processes auto;
daemon on;
master_process on;
error_log logs/mos_error.tcp debug_tcp;
error_log logs/mos_error.log;
pid /opt/imail/nginx/logs/mos_nginx.pid;
worker_rlimit_nofile 200000;
worker_rlimit_core 500M;
working_directory /opt/imail/nginx;
events {
worker_connections 25000;
use epoll;
multi_accept off;
}
http {
log_format testlogs '$remote_addr - $remote_user [$time_local] '
'"$request" $status $body_bytes_sent '
'"$http_referer" "$upstream_addr" '
'$request_time $upstream_response_time';
access_log logs/mos_access.log;
sendfile on;
keepalive_requests 500000;
keepalive_timeout 20s;
tcp_nopush on;
tcp_nodelay on;
client_body_buffer_size 128k;
client_body_temp_path /dev/shm/mos_nginx/client_temp 1 2;
open_file_cache max=25000 inactive=30s;
open_file_cache_valid 60s;
open_file_cache_min_uses 2;
open_file_cache_errors on;
upstream mosgenericbackend {
server mss1:8081;
server mss2:8081;
server mss3:8081;
server mss4:8081;
healthcheck_enabled;
healthcheck_delay 1000;
healthcheck_timeout 1000;
healthcheck_failcount 2;
healthcheck_send 'GET /mxos/monitor HTTP/1.0';
keepalive 300;
}
server {
listen 8081;
keepalive_timeout 600s;
client_max_body_size 0;
location /mxos/ {
proxy_http_version 1.1;
proxy_set_header Connection "";
proxy_pass http://mosgenericbackend;
proxy_connect_timeout 2;
more_set_headers "Content-Type: application/json";
}
location /mxos/health_status {
healthcheck_status;
}
proxy_connect_timeout 60;
proxy_read_timeout 30;
proxy_send_timeout 60;
}
}

My [vendor patched/supplied due to application specific load balancing+health check] nginx version:

# /opt/imail/nginx/sbin/nginx -V
nginx version: nginx/1.7.4
built by gcc 3.4.6 20060404 (Red Hat 3.4.6-3)
TLS SNI support disabled
configure arguments: --with-debug --add-module=/bld/current/emailmx90_git_blds/emailmx90_contrib_shared/contrib/nginx_1.7.4/source/addons/healthcheck_nginx_upstreams-master --add-module=/bld/current/emailmx90_git_blds/emailmx90_contrib_shared/contrib/nginx_1.7.4/source/addons/headers-more-nginx-module-0.23 --add-module=/bld/current/emailmx90_git_blds/emailmx90_contrib_shared/contrib/nginx_1.7.4/source/addons/yaoweibin-nginx_tcp_proxy_module-f2156ef