Nginx Delay Module

Introduction

The ngx_http_delay module is authored by Maxim Dounin, member of the core Nginx team.

Maxim mantains a mercurial repository with the latest version of the code.

This module enables a delay directive to be used when serving a request. This can be of use for limiting the rate of requests without signaling a 503 Service Unavailable to the client.

It can also be used to perform abuse control. It's not hard to imagine a script that coordinate with a TCP traffic analysis reloads the Nginx configuration inserting a delay directive wherever necessary.

Here's an example configuration:

location / {
    error_page 418 @abuse;
    if ($is_abusing) {
        return 418;
    }
    # other stuff here...
}

## Abusers get a delay of 5s.
location @abuse {
    delay 5s;
    
    # other stuff here...
}

the $is_abusing variable gets a non-zero value following a criteria you choose.

You can compound delays by issuing an internal redirect. In the above example if we have a serious abuser we can do a further redirect to get a 10s delay right of the bat.

recursive_error_pages on; 

location @abuse {
    delay 5s;
    
    error_page 418 @serious-abuse;
    if ($is_serious_abuser) {
        return 418;
    }
    
    # other stuff here...
}

location @serious-abuse {
    delay 1m; # delay 1 minute
    
    # other stuff here...
}

So he have a 10s + 1m delay, giving a 70s total delay.

Module directives

delay <time specification>

default: 0

context: http, server, location

Inserts a delay of the specified duration when serving a request.

Installation

1. Grab the source from the mercurial tip or clone this repo:

   git clone git://github.com/perusio/nginx-delay-module.git
   

2. 2. Add the module to the build configuration by adding --add-module=/path/to/ngx_http_delay_module.

3. Build the nginx binary.

4. Install nginx binary.

5. Configure contexts where delay is enabled.

6. Done.

Other possible uses

One other possible use is for doing poor man's traffic shapping.

Opinionated scholium

This is yet another example of using a very simple module that can perform an action useful in security terms. There's no need for bloated mod_security like mess.

Other Maxim Dounin Nginx modules on Github

• Nginx Auth Request: allows for subrequests in an authorization. Can be used for request filtering or two-factor authentication for example.