README.md

Lwan Web Server

Lwan is a high-performance & scalable web server for glibc/Linux platforms.

The project web site contains more details.

Build status

OS Arch Release Debug Static Analysis Tests Linux x86_64 Report history Linux armv7

FreeBSD x86_64

macOS x86_64

Building

Before installing Lwan, ensure all dependencies are installed. All of them are common dependencies found in any GNU/Linux distribution; package names will be different, but it shouldn't be difficult to search using whatever package management tool that's used by your distribution.

Required dependencies

• CMake, at least version 2.8
• ZLib

Optional dependencies

The build system will look for these libraries and enable/link if available.

• Lua 5.1 or LuaJIT 2.0
• TCMalloc
• jemalloc
• Valgrind
• To run test suite:
  • Python (2.6+) with Requests
  • Lua 5.1
• To run benchmark:
  • Special version of Weighttp
  • Matplotlib
• To build TechEmpower benchmark suite:
  • Client libraries for either MySQL or MariaDB
  • SQLite 3

Common operating system package names

Minimum to build

• ArchLinux: pacman -S cmake zlib
• FreeBSD: pkg install cmake pkgconf
• Ubuntu 14+: apt-get update && apt-get install git cmake zlib1g-dev pkg-config

Build all examples

• ArchLinux: pacman -S cmake zlib sqlite luajit libmariadbclient gperftools valgrind
• FreeBSD: pkg install cmake pkgconf sqlite3 lua51
• Ubuntu 14+: apt-get update && apt-get install git cmake zlib1g-dev pkg-config lua5.1-dev libsqlite3-dev libmysqlclient-dev

Build commands

Clone the repository

~$ git clone git://github.com/lpereira/lwan
~$ cd lwan

Create the build directory

~/lwan$ mkdir build
~/lwan$ cd build

Select build type

Selecting a release version (no debugging symbols, messages, enable some optimizations, etc):

~/lwan/build$ cmake .. -DCMAKE_BUILD_TYPE=Release

If you'd like to enable optimiations but still use a debugger, use this instead:

~/lwan/build$ cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo

To disable optimizations and build a more debugging-friendly version:

~/lwan/build$ cmake .. -DCMAKE_BUILD_TYPE=Debug

Build Lwan

~/lwan/build$ make

This will generate a few binaries:

• src/bin/lwan/lwan: The main Lwan executable. May be executed with --help for guidance.
• src/bin/testrunner/testrunner: Contains code to execute the test suite.
• src/samples/freegeoip/freegeoip: FreeGeoIP sample implementation. Requires SQLite.
• src/samples/techempower/techempower: Code for the Techempower Web Framework benchmark. Requires SQLite and MySQL libraries.
• src/bin/tools/mimegen: Builds the extension-MIME type table. Used during build process.
• src/bin/tools/bin2hex: Generates a C file from a binary file, suitable for use with #include.

Remarks

Passing -DCMAKE_BUILD_TYPE=Release will enable some compiler optimizations (such as LTO) and tune the code for current architecture. Please use this version when benchmarking, as the default is the Debug build, which not only logs all requests to the standard output, but does so while holding a mutex.

The default build (i.e. not passing -DCMAKE_BUILD_TYPE=Release) will build a version suitable for debugging purposes. This version can be used under Valgrind (if its headers are present), is built with Undefined Behavior Sanitizer, and includes debugging messages that are stripped in the release version. Debugging messages are printed for each and every request.

Which sanitizer will be used in a debug build can be selected by passing the following arguments to the CMake invocation line:

• -DSANITIZER=ubsan selects the Undefined Behavior Sanitizer.
• -DSANITIZER=address selects the Address Sanitizer.
• -DSANITIZER=thread selects the Thread Sanitizer.

Tests

~/lwan/build$ make teststuite

This will compile the testrunner program and execute regression test suite in src/scripts/testsuite.py.

Benchmark

~/lwan/build$ make benchmark

This will compile testrunner and execute benchmark script src/scripts/benchmark.py.

Coverage

Lwan can also be built with the Coverage build type by specifying -DCMAKE_BUILD_TYPE=Coverage. This enables the generate-coverage make target, which will run testrunner to prepare a test coverage report with lcov.

Every commit in this repository triggers the generation of this report, and results are publicly available.

Running

Set up the server by editing the provided lwan.conf; the format is very simple and should be self-explanatory.

Configuration files are loaded from the current directory. If no changes are made to this file, running Lwan will serve static files located in the ./wwwroot directory. Lwan will listen on port 8080 on all interfaces.

Lwan will detect the number of CPUs, will increase the maximum number of open file descriptors and generally try its best to autodetect reasonable settings for the environment it's running on.

Optionally, the lwan binary can be used for one-shot static file serving without any configuration file. Run it with --help for help on that.

Portability

While Lwan was written originally for Linux, it has been ported to BSD systems as well. The build system will detect the supported features and build support library functions as appropriate.

For instance, epoll has been implemented on top of kqueue, and Linux-only syscalls and GNU extensions have been implemented for the supported systems.

Performance

It can achieve good performance, yielding about 320000 requests/second on a Core i7 laptop for requests without disk access, and without pipelining.

When disk I/O is required, for files up to 16KiB, it yields about 290000 requests/second; for larger files, this drops to 185000 requests/second, which isn't too shabby either.

These results, of course, with keep-alive connections, and with weighttp running on the same machine (and thus using resources that could be used for the webserver itself).

Without keep-alive, these numbers drop around 6-fold.

IRC Channel

There is an IRC channel (#lwan) on Freenode. A standard IRC client can be used. A web IRC gateway is also available.

Lwan in the wild

Here's a non-definitive list of third-party stuff that uses Lwan and have been seen in the wild. Help build this list!

• This project uses Cython and Lwan to make it possible to write handlers in Python.
• An experimental version of Node.js using Lwan as its HTTP server is maintained by @raadad.
• The beginnings of a C++11 web framework based on Lwan written by @vileda.
• A more complete C++14 web framework by @matt-42 offers Lwan as one of its backends.
• A word ladder sample program by @sjnam. Demo.
• A Shodan search listing some brave souls that expose Lwan to the public internet.

Some other distribution channels were made available as well:

• A Dockerfile is maintained by @jaxgeller, and is available from the Docker registry.
• A buildpack for Heroku is maintained by @bherrera, and is available from its repo.
• Lwan is also available as a package in Biicode.
• It's also available in some GNU/Linux distributions:
  • Arch Linux
  • Ubuntu
  • Alpine Linux
  • NixOS

Lwan has been also used as a benchmark:

• Raphael Javaux's master thesis cites Lwan in chapter 5 ("Performance Analysis").
• Lwan is used as a benchmark by the PyParallel author.
• Kong uses Lwan as the backend API in its benchmark.
• TechEmpower Framework benchmarks feature Lwan since round 10.
• KrakenD used Lwan for the REST API in all official benchmarks

Mentions in academic journals:

• A dynamic predictive race detector for C/C++ programs uses Lwan as a "real world example".

Some talks mentioning Lwan:

• Talk about Lwan at Polyconf16, given by @lpereira.
• This talk about Iron, a framework for Rust, mentions Lwan as an insane C thing.
• University seminar presentation about Lwan.
• This presentation about Sailor web framework mentions Lwan.
• Performance and Scale @ Istio Service Mesh, at around 7:30min, presented at KubeCon Europe 2018, mentions that Lwan is used on the server side for testing due to its performance and robustness.

Not really third-party, but alas:

• The author's blog.
• The project's webpage.

Lwan quotes

These are some of the quotes found in the wild about Lwan. They're presented in no particular order. Contributions are appreciated:

"I read lwan's source code. Especially, the part of using coroutine was very impressive and it was more interesting than a good novel. Thank you for that." -- @patagonia

"For the server side, we're using Lwan, which can handle 100k+ reqs/s. It's supposed to be super robust and it's working well for us." -- @fawadkhaliq

"Insane C thing" -- Michael Sproul

"I've never had a chance to thank you for Lwan. It inspired me a lot to develop Zewo" -- @paulofariarl

"Let me say that lwan is a thing of beauty. I got sucked into reading the source code for pure entertainment, it's so good. high five" -- @kwilczynski

"Nice work with Lwan! I haven't looked that carefully yet but so far I like what I saw. You definitely have the right ideas." -- @thinkingfish

"Lwan is a work of art. Every time I read through it, I am almost always awe-struck." -- @neurodrone

"For Round 10, Lwan has taken the crown" -- TechEmpower