FQ Pacing Plugin

This is a remap plugin that allows ATS to rate limit an individual TCP connection. It is based on Linux support for the Fair Queuing qdisc. FQ and SO_MAX_PACING_RATE is available in RedHat/Centos 7.2+, Debian 8+, and any other Linux distro with a kernel 3.18 or greater.

How it Works

When activated during remap processing, this plugin calls setsockopt(SO_MAX_PACING_RATE) on the client socket. To prevent the rate from leaking to other remap rules the client may access in future requests, a hook is set to deactivate the pacing when the current transaction completes.


First, enable the FQ qdisc by setting net.core.default_qdisc=fq in /etc/sysctl.conf and rebooting.

The FQ Pacing plugin is a remap plugin. Enable it by adding fq_pacing.so to your remap.config file. Provide a --rate=BytesPerSec option to set the maximum rate of a TCP connection matching that remap line.

Here is an example remap.config entry:

map http://reverse-fqdn.com http://origin.com @plugin=fq_pacing.so @pparam=--rate=100000