An A/B testing work-in-progress

nginx.conf

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;

# Load dynamic modules. See /usr/share/nginx/README.dynamic.
include /usr/share/nginx/modules/*.conf;

events {
    worker_connections 1024;
}

http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile            on;
    tcp_nopush          on;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 2048;

    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    # weighted routing
    split_clients "${date_gmt}${arg_random}"    $split_site {
        50%                    "old";
        *                      "new";
    }
    map $cookie_DYN_USER_ID     $selector_dynuserid {
        default                 "dynuserid";  # This will only match non-empty values because of the match below
        ""                      "";           # This is technically the default because it matches an empty value
    }

    map $cookie_site_upstream   $selector_cookie {
        "old"                   "cookie";
        "new"                   "cookie";
    }

    map $arg_site               $selector_arg {
        "old"                   "arg";
        "new"                   "arg";
    }

    map "$selector_dynuserid$selector_cookie$selector_arg"  $use_selector {
        default                 "split";
        "arg"                   "arg";
        "cookie"                "cookie";
        "dynuserid"             "dynuserid";
    }

    map $use_selector           $site_upstream {
        "arg"                   $arg_site;
        "cookie"                $cookie_site_upstream;
        "dynuserid"             "old";
        "split"                 $split_site;
    }

    map $use_selector           $site_upstream_cookie {
        default                 "$site_upstream; Path=/; Max-Age=604800"; # 60seconds * 60minutes * 24hours * 7days = 604800
        "dynuserid"             "deleted; Path=/; Expires=Thu, 01 Jan 1970 00:00:00 GMT";
    }

    map $site_upstream          $site_host {
        default                 "503"; # This should never happen
        "old"                   "www.example-a.com";
        "new"                   "www.example-b.com";
    }

    server {
        listen         8080 default_server;
        listen         [::]:8080 default_server;
        server_name    _;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
            include /etc/nginx/debug_headers.d/*.conf;
            add_header Set-Cookie "site_upstream=$site_upstream_cookie";
            #include /etc/nginx/debug_here.conf;
            include /etc/nginx/proxy_settings.conf;
            proxy_pass https://$site_host;
        }

        error_page      404 /404.html;
            location = /40x.html {
        }

        error_page      500 502 503 504 /50x.html;
            location = /50x.html {
        }
    }
}