NAME

       vmod_vsthrottle - Throttling VMOD

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

       • BOOL is_denied(STRING, INT, DURATION)

       • INT remaining(STRING, INT, DURATION)

   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);
                 }

                                                                               VMOD_VSTHROTTLE(3)