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A DNS performance and functional testing utility.

2017-2022© NSONE, Inc.


Flamethrower is a small, fast, configurable tool for functional testing, benchmarking, and stress testing DNS servers and networks. It supports IPv4, IPv6, UDP, TCP, DoT, and DoH and has a modular system for generating queries used in the tests.

Originally built as an alternative to dnsperf, many of the command line options are compatible.

Getting Started

The easiest way to get started with Flamethrower is to use the public docker image:

docker pull ns1labs/flame
docker run ns1labs/flame --help

There are currently no prebuilt operating system packages. If you would like to build your own executable, please see the Build section below.


Current command line options are described with:

flame --help

Quick Examples

Flame localhost port 53, UDP, maximum speed:

flame localhost

Flame target, port 5300, TCP:

flame -p 5300 -P tcp

Flame target, port 443, DoT:

flame -p 443 -P dot

Flame target, DNS over HTTPS GET:

flame -P doh

Flame target, DNS over HTTPS POST:

flame -P doh -M POST

Flame target with random labels:

flame -g randomlabel lblsize=10 lblcount=4 count=1000

Flame multiple target at once, reading the list from a file:

flame file --targets myresolvers.txt

Detailed Features

Query Generators

Flamethrower uses a modular system for generating queries. Most modules generate all queries before sending begins, for performance reasons. Each module may include its own list of configuration options which can be set via key/value pairs on the command line. See full --help for the current list of generators and their options.

Rate Limiting

By default, Flamethrower will send traffic as fast as possible. To limit to a specific overall queries per second, use -Q

Dynamic QPS Flow

Flamethrower can adjust its QPS flow over time. This is useful for generating a "signal" of traffic (e.g. a square wave) for calibrating metrics collection. For example, to send 10 QPS for 120000ms, then 80 QPS for 120000ms, etc use --qps-flow "10,120000;80,120000;10,120000;". Flow change will not loop, you should list as many changes as necessary. Once the flow reaches the final QPS number, it will hold it until program termination.

Output Metrics

Flamethrower can generate detailed metrics for each of its concurrent senders. Metrics include send and receive counts, timeouts, min, max and average latency, errors, and the like. The output format is JSON, and is suitable for ingestion into databases such as Elastic for further processing or visualization. See the -o flag.


Flamethrower is single threaded, async i/o. You specify the amount of concurrent senders with the -c option. Each of these senders will send a configurable number of consecutive queries (see -q), then enter a configurable delay period (see -d) before looping.

Each concurrent sender will pull the next query from the total queries generated by the Query Generator, looping once it reaches the end of the query list (if the program is configured to continue).

There is currently no built-in support for multiprocess sending, so the maximum throughput will be reached once a single CPU is saturated. However, you may manually start several concurrent flame processes, including up to 1 per CPU available. There is future planned support for builtin multiprocess sending.

Build Dependencies

  • CMake >= 3.8
  • Linux or OSX
  • libuv >= 1.30.0
  • libldns >= 1.7.0
  • gnutls >= 3.3
  • C++ compiler supporting C++17

Optional DoH support requires:

  • nghttp2

Optional dependencies:

  • docopt
  • nlohmann-json >= 3.7.3
  • cpp-httplib
  • uvw >= 1.18.0


Building is based on CMake.

Default build:

mkdir build; cd build
cmake ..

To build with DoH support:

mkdir build; cd build
cmake -DDOH_ENABLE=ON ..

Building the docker image:

docker build . --tag ns1labs/flame --file Dockerfile
docker run --rm --net host ns1labs/flame --help


Pull Requests and issues are welcome. See the NS1 Contribution Guidelines for more information.


This code is released under Apache License 2.0. You can find terms and conditions in the LICENSE file.