configuration nginx docs

server
{
  listen      80 default_server;
  listen      [::]:80 default_server ipv6only=on;
  server_name graylog.example.org;

  location /api/
    {
        proxy_set_header    Host $http_host;
        proxy_set_header    X-Forwarded-Host $host;
        proxy_set_header    X-Forwarded-Server $host;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_pass          http://127.0.0.1:12900/;
    }
  location /
    {
        proxy_set_header    Host $http_host;
        proxy_set_header    X-Forwarded-Host $host;
        proxy_set_header    X-Forwarded-Server $host;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header    X-Graylog-Server-URL http://graylog.example.org/api;
        proxy_pass          http://127.0.0.1:9000;
    }
}

configuration with ssl

server
{
  listen 443 ssl spdy;
  server_name ess-lon-graylogweb-001;
  ssl_certificate
  ssl_certificate_kex

  location /api/
    {
        proxy_set_header    Host $http_host;
        proxy_set_header    X-Forwarded-Host $host;
        proxy_set_header    X-Forwarded-Server $host;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_pass          http://127.0.0.1:12900/;
    }
  location /
    {
        proxy_set_header    Host $http_host;
        proxy_set_header    X-Forwarded-Host $host;
        proxy_set_header    X-Forwarded-Server $host;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header    X-Graylog-Server-URL https://ess-lon-graylogweb-001/api;
        proxy_pass          http://127.0.0.1:9000;
    }
}