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daa4f1d Sep 21, 2016
@daghf @Dridi
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vmod_vsthrottle

Throttling VMOD

Manual section:3

SYNOPSIS

import vsthrottle [from "path"] ;

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.

Example:

vcl 4.0;
import vsthrottle;

backend default { .host = "192.0.2.11"; .port = "8080"; }

sub vcl_recv {
    # Varnish will set client.identity for you based on client IP.

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

    # There is a quota per API key that must be fulfilled.
    if (vsthrottle.is_denied("apikey:" + req.http.Key, 30, 60s)) {
            return (synth(429, "Too Many Requests"));
    }

    # Only allow a few POST/PUTs per client.
    if (req.method == "POST" || req.method == "PUT") {
        if (vsthrottle.is_denied("rw" + client.identity, 2, 10s)) {
            return (synth(429, "Too Many Requests"));
        }
    }
}

CONTENTS

  • func_is_denied
  • func_remaining

is_denied

BOOL 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
Description
Can be used to rate limit the traffic for a specific key to a maximum of 'limit' requests per 'period' time. A token bucket is uniquely identified by the triplet of its key, limit and period, so using the same key multiple places with different rules will create multiple token buckets.
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"));
        }

        # ...
}

remaining

INT remaining(STRING key, INT limit, DURATION period)
Arguments:
  • key: A unique identifier to define what is being throttled
  • limit: How many requests in the specified period
  • period: The time period

Description

Get the current number of tokens for a given token bucket. This can be used to create a response header to inform clients of their current quota.
Example
sub vcl_deliver {
   set resp.http.X-RateLimit-Remaining = vsthrottle.remaining(client.identity, 15, 10s);
}