vmod_vsthrottle

Varnish Throttling Module

Author:	Dag Haavi Finstad
Date:	2014-04-17
Version:	1.0
Manual section:	3

SYNOPSIS

import vsthrottle;

DESCRIPTION

A Varnish vmod for rate-limiting traffic on a single Varnish server. Offers a simple interface for throttling traffic on a per-key basis to a specific request rate.

Keys can be specified from any VCL string, e.g. based on client.ip, a specific cookie value, an API token, etc.

The request rate is specified as the number of requests permitted over a period. To keep things simple, this is passed as two separate parameters, 'limit' and 'period'.

This VMOD implements a token-bucket algorithm. State associated with the token bucket for each key is stored in-memory using BSD's red-black tree implementation.

Memory usage is around 100 bytes per key tracked.

FUNCTIONS

is_denied

Prototype

is_denied(STRING key, INT limit, DURATION period)

Arguments

key: A unique identifier to define what is being throttled - more examples below

limit: How many requests in the specified period

period: The time period

Return value

BOOL

Description

Can be used to rate limit the traffic for a specific key to a maximum of 'limit' requests per 'period' time.

Example

sub vcl_recv {
        if (vsthrottle.is_denied(client.identity, 15, 10s)) {
                # Client has exceeded 15 reqs per 10s
                return (synth(429, "Too Many Requests"));
        }

        # ...
}

INSTALLATION

To be able to compile this vmod, varnish 4 must be installed, and the source tree must be locally available.

The source tree is based on autotools to configure the building, and does also have the necessary bits in place to do functional unit tests using the varnishtest tool.

Pre-installation configuration:

./autogen.sh
./configure VARNISHSRC=DIR [VMODDIR=DIR]

VARNISHSRC is the directory of the Varnish source tree for which to compile your vmod. Both the VARNISHSRC and VARNISHSRC/include will be added to the include search paths for your module.

Optionally you can also set the vmod install directory by adding VMODDIR=DIR (defaults to the pkg-config discovered directory from your Varnish installation).

Make and install the vmod:

make           # builds the vmod
make install   # installs your vmod in `VMODDIR`
make check     # runs the unit tests in ``src/tests/*.vtc``

The libvmod-vsthrottle vmod will now be available in your VMODDIR and can be copied to other systems as required.

USAGE

In your VCL you can now use this vmod along the following lines:

import vsthrottle;

sub vcl_recv {
        if (vsthrottle.is_denied(client.identity, 15, 10s)) {
        # Client has exceeded 15 reqs per 10s
        return (synth(429, "Too Many Requests"));
        }
}

ADDITIONAL VMODS

For further examples and inspiration check the vmod directory: https://www.varnish-cache.org/vmods

COPYRIGHT

This document is licensed under the same license as the libvmod-example project. See LICENSE for details.

annaken/libvmod-vsthrottle