Example nginx load balancer

load-balancer.conf

## Global parameters

## StatsD Plugin: https://github.com/zebrafishlabs/nginx-statsd
statsd_server statsd.domain.tld;

# Stop proxying to an upstream if any of these happen
proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;

# Setup standard forwarding headers
proxy_set_header Accept-Encoding "";
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;

# For keepalive
proxy_http_version 1.1;
proxy_set_header Connection ""; ## Override for websockets

# Don't redirect, proxy!
proxy_redirect off;

## Force HTTPS
server {
  # default_server says to route to this server if none are available
  listen 80 default_server;
  statsd_count "prefix.lb.forcehttps.requests" 1;
  
  # rewrite a 301 for HTTPS forcing
  rewrite ^ https://$host$request_uri? permanent;
}

## Catch-all server to respond 404 to any erroneous request
server {
  # any request not routed to another server will go here and get 404'd
  listen 443 default_server;

  ssl on;
  ## <snip>ssl options...</snip>
  
  statsd_count "prefix.lb.erroneous.requests" 1;
  return 404 "Not Found";
}

## Setup our first load balanced domain
upstream application {
  ## We usually use /etc/hosts for these IPs. You could hard-code or use internal DNS for it.
  instance-01.application.production.domain.tld;
  instance-02.application.production.domain.tld;
  instance-03.application.production.domain.tld;
  
  ## Allows 32 connections to be kept alive to the backend servers
  # This speeds up services with repeated requests
  # but adds on open connections
  keepalive 32;
}

## Load balanced application server
server {
  listen 443;
  server_name application.domain.tld;
  
  ssl on;
  ## <snip> ssl options... </snip>
  
  # Count requests to this domain
  statsd_count "prefix.lb.application.https.requests" 1;

  access_log /var/log/nginx/application-access.log;
  error_log /var/log/nginx/application-error.log;

  location / {
    # Keep a timing record to notice spikes
    statsd_timing "prefix.lb.application.https.response_time" "$upstream_response_time";

    # The actual proxying!
    proxy_pass http://application;
  }
}