Friday, June 24, 2016

H2O HTTP/2 server 2.0.1 / 2.1.0-beta1 released, with new features and performance optimizations

Today I am happy to announce the release of H2O HTTP/2 server version 2.0.1 and 2.1.0-beta1.

Version 2.0.1 is a bug-fix release of the 2.0 series. Existing users can upgrade to the new version to avoid the issues listed in the changeling.

Version 2.1.0-beta1 is the first beta release of 2.1, with a new throttle-response handler for per-response bandwidth throttling, and an enhancement to the status handler (pull #893). It also includes two new features that improve HTTP/2 performance: TCP latency optimization and support for link: rel=preload headers in informational response (pull #916).

With TCP latency optimization, users can expect 1 RTT or more reduction in time-to-render if the main resource (i.e. HTML) is much larger INITCWND (typically ~15KB).

The reduction comes from the fact that with the optimization enabled, H2O tries to keep the amount of HTTP/2 frames kept unsent in the TCP send buffer very small (to just two packets) during the slow-start phase. Since the amount of data unsent is kept small, the server can switch to sending a resource that blocks the rendering path (e.g. CSS) immediately when it receives a request for such resource, instead of pushing the HTML body stored in the TCP send buffer. As CWND grows, the connection handling switches to bandwidth-optimization mode, that pre-fills more data into the send buffer so that the kernel can send additional data immediately after receiving ACKs without user-space intervention.

Support for link: rel=preload headers in informational response helps web developers utilize HTTP/2 push. Use of the link header is becoming the standard way to instruct HTTP/2 servers to start pushing assets. The downside of the approach is that application servers typically cannot send the header until it generates the final response. Generation of the final response often involves time-consuming operations such as access to the database, keeping the HTTP/2 connection idle for that period.

Use of informational response lets us use the time slot for pushing asset files. Application servers can now send an informational response with link rel=preload headers to H2O to start pushing the asset files, then perform heavy tasks, and send the final response. Use of 1xx response will not cause interoperability issues, since only the final response is sent to the client connected to H2O.

Details of the two optimizations were covered in my presentation at Tokyo RubyKaigi 11. The slides are shown below:

Wednesday, June 1, 2016

H2O HTTP2 server 2.0 released!

We are happy to announce the release of H2O version 2.0.

It is a major update from 1.7 series, including many improvements and bug fixes.

The most prominent changes are:Full list of changes can be found here. Please refer to the reference documentation to find out how to use them.

Have fun!

Thursday, May 26, 2016

H2O version 1.7.3 / 2.0.0-beta5 released with a vulnerability fix

We have just released version 1.7.3 and 2.0.0-beta5 of the H2O HTTP/2 server.

The releases include a fix for a security issue (CVE-2016-4817). Existing users are encouraged to update their installations.

The details of the issue can be found here.

We would like to thank Tim Newsham for reporting the issue and Frederik Deweerdt for providing a fix.

Monday, May 9, 2016

H2O HTTP/2 server 1.7.2 / 2.0.0-beta3 released

Today I have released H2O HTTP/2 server version 1.7.2 and 2.0.0-beta3.

The releases include an updated version of LibreSSL that fixes CVE-2016-2107; users of H2O built with the bundled version of LibreSSL are advised to update their installations.

In addition to the fix, 2.0.0-beta3 includes many new features and bug fixes.

Especially, support for reverse-proxying over HTTPS (#875) and the new configuration directives for tweaking environment variables passed to FastCGI (#868) might be helpful to the users who have wanted them.

We plan to release the final version of 2.0 soon, and then proceed to optimizing the server even further. Stay tuned!

Wednesday, March 23, 2016

H2O version 2.0.0-beta2 released, with a new "status" handler

Today I am happy to announce the release of H2O HTTP/2 server version 2.0.0-beta2.

The release comes with the new status handler that shows the HTTP requests in-flight. Now, you can monitor what's going on inside H2O!

Some notable features are:
  • both HTTP/1 and HTTP/2 requests are shown
  • HTTP/2 priorities are shown
  • the screen can be updated automatically by clicking the Refresh checkbox


Under the hood, the status is served via a JSON API (lib/handler/status.c L169), and rendered by a static HTML document(share/h2o/status/index.html). So it would be easy for anyone to extend the status or retrieve and use the status from another program.

The documentation of the status handler can be found here.

Thursday, March 17, 2016

File-level mapping introduced in H2O version 2.0

As the developer of H2O, the lack of ability to define a mapping for a specific path (not a directory) has been one of the complaints I hear the most. Finally, we have a fix for the issue, and that is why the next release will be given the number 2.0.

Starting from H2O version 2.0.0beta-1, it is possible to write a configuration like the following. The example maps all requests to a FastCGI server, with the exception of /robots.txt and /favicon.ico being served statically.
paths:
  /:
    fastcgi.connect:
      port: /tmp/fcgi.sock
      type: unix
  /robots.txt:
    file.file: /path/to/robots.txt
  /favicon.ico:
    file.file: /path/to/favicon.png
Pretty straight forward, isn't it?

For details, please refer to the updated documentation of paths directive, or refer to the discussion in the pull request.

Tuesday, March 15, 2016

H2O HTTP/2 server goes 2.0 adding support for Brotli

Today, I am happy to announce the release of H2O version 2.0.0-beta1, the first release of the 2.0 series. In the release, we have added support for Brotli in two ways.

For those who do not know, Brotli is a new compression method developed by Google. It is said to compress files ~20% smaller than gzip - means less bandwidth consumed and faster rendering on the client side. Mozilla has already added support for Brotli in Firefox 44, and Chrome is gradually turning the knob on as well.

Starting with H2O version 2.0.0-beta1, when the file.send-compressed directive is set to ON, the server sends a file with .br or .gz suffix instead of file being requested should such file exist. For example, if index.html is requested with a Accept-Encoding: br request header, and if a file named index.html.br exists, the server sends the contents of index.hmtl.br as the response with the Content-Encoding: br response header being set. In case the client is capable of decompressing both algorithms both algorithms and if both of .br and .gz files exist, the .br file is selected as the response.
# send pre-compressed files (.br or .gz)
file.send-compressed: ON

The other directive: compress controls on-the-fly compression. When turned on, it compresses the response as it is being sent to the client, using either brotli or gzip depending on the configuration and browser support. This can be used for compressing output from PHP and other dynamically-generated content.
# perform on-the-fly compression (brotli or gzip)
compress: [ brotli, gzip ]
Server administrators may also be interested in fine-tuning the compression quality of the compression methods. The following configuration sets the compression quality of brotli to 4 and gzip to 6, a suggested setting by Understanding Brotli's Potential - The Akamai Blog. The compression speed becomes about half of the default (1 for both gzip and brotli), but the size of the content after compression is expected to become ~15% smaller for both methods.
# perform more effective (but CPU-intensive) compression
compress:
  brotli: 4
  gzip:   6

In my upcoming blogposts I will cover other changes in the 2.0 release of H2O. Stay tuned!