Tune The Web

Setting up HTTP/2 on your web server

Introduction to HTTP/2

Hypertext Transfer Protocol (HTTP) is the way your web browser talks to a web server to ask for web pages and the resources they need. At it's heart it's a very simple protocol and has not moved on much in the last 20 years since HTTP/1.1 came on the scene in 1996 (HTTP/1.0 was very basic and almost immediately superseded by 1.1 as the world wide web was becoming mainstream so we'll ignore it). For various reasons it's showing it's age and is causing a performance bottleneck in today's world of rich web pages and applications. This has led to several work arounds which have their own drawbacks. HTTP/2 is the next version of the protocol which aims to address a lot of the issues we have seen. And apparently it is written HTTP/2 and not HTTP 2 or HTTP/2.0

Why do we need HTTP/2?

The main issue with HTTP/1.1 is that it is, basically synchronous. This means you request a resource from a web server (be it a web page, an image, a stylesheet...etc.) and you have to wait for a response. Typically a web page has many resources on it, so after you have downloaded the original webpage, you have a queue of resources to request from the web server. Most web resources are not actually that large, so a lot of that waiting time will be simply waiting for the request to travel across the internet and back. As websites and web applications get richer and richer this gets more and more of a problem. The average page size now has 100 requests in it. Now it still only takes milliseconds to travel have and forth but those start to add up when you have 100 resources to download. Imagine wanting to order several books from Amazon and having to wait for each to arrive, before you could order the next book - a crazy way of doing it, but that's basically what HTTP/1.1 does. It would be much better to fire off all requests to Amazon and it can ship them out to you as fast as it can (ignoring postage costs) and HTTP/2 works like that. There are several workarounds though that are currently used for HTTP/1.1:

All of these are hacks because of a fundamental issue with HTTP/1.1. It would be much better to fire off all the requests, and then deal with them as they come in. HTTP/2 allows this and therefore drastically reduces the need for the hacks and the downsides I have listed above.

HTTP/2 also has some other benefits including: It's a binary rather than text based protocol, it allows compression of HTTP Headers, it allows the server to push requests (e.g. if you ask for the home page, it might push the stylesheet and other resources it knows you will need). This last one will be interesting but is not widely supported yet. The main benefit at present is the ability to send and receive a number of requests at once. I've a separate post about HTTP/2 Server Push.

How to set up HTTP/2 on Apache from source

HTTP/2 is starting to become available for web servers in the last few weeks and months so it is not quite mainstream yet. HTTP/2 is heavily based on the SPDY protocol, which came out of Google, which is a bit more common in some web servers but it has officially been retired and will no longer be supported in Chrome after May 15th, so I would not recommend installing that now.

HTTP/2 also requires HTTPS so if you don't run that on your server, there is little point in continuing until you get that set up. Well to be honest, technically the spec doesn't require HTTPS but all browser vendors have said they will only support this over HTTPS so it might as well. Additionally some browsers also requires a decent HTTPS set up with modern ciphers. The HTTP/2 spec blacklists a number of older ciphers and so some browsers (e.g. Chrome) will give an error if you try to use HTTP/2 when your server is configured to use these ciphers. HTTP/2 also requires a fairly recent version of openssl (1.0.2 or above) - which also means you've now excuse not to use a decent cipher list :-)

I will list the steps to install HTTP/2 on Apache below, however I should sound a huge word of caution here: HTTP/2 support in a lot of web servers (Apache included) is still very bleeding edge and is not yet recommended in a production environment! Install at your own risk. However it can be good to install on a test server to start seeing the impact it will have, and if you run a simple blog like this one, maybe you'll be happy to take the risk. Just don't say I didn't warn you!

Apache is usually installed as part of package manager on Linux (e.g. yum or apt-get) but these often lag behind the latest versions, so, while you might be lucky enough to be on a linux install with the latest Apache version (Debian seems very up to date for example), it's likely you will need to download and compile the source code to get the latest version. This sounds more intimidating that it really is however I will advise that should only be attempted by experienced system administrators. Package Managers allow you to easily keep on top of security patches whereas installing from source does not. Additionally source packages should be verified to ensure they have not been tampered with when downloading them, which is not covered in these steps (see the Apache documentation on how to verify files). With that out of the way, the below commands will download and install Apache 2.4.25 into the default /usr/local/apache2 directory and enable HTTP/2 support on Centos or Red Hat Linux:

#You may need to install some dependencies if not already installed on your machine. #For Centos/RHEL 7 the following should do this for you: sudo yum install wget sudo yum install perl sudo yum install gcc sudo yum install pcre-devel cd ~ mkdir sources cd sources #Install latest version of openssl 1.0.2 #Note mod_http2 requires at least openssl 1.0.2 #Note that at the time of writing Apache httpd does not yet compile with the newly released openssl 1.1.0. #Get it from http://openssl.org/source/ #For example: #wget https://www.openssl.org/source/openssl-1.0.2j.tar.gz #wget https://www.openssl.org/source/openssl-1.0.2j.tar.gz.asc #Verify the package after download (not covered here but can be done with: gpg --verify openssl-1.0.2j.tar.gz.asc) tar -zxvf openssl-1.0.2j.tar.gz cd openssl-1.0.2j ./config shared zlib-dynamic make sudo make install cd .. #Install nghttp2 (needed for mod_http2). #Get it from https://nghttp2.org/ #Latest version here: https://github.com/nghttp2/nghttp2/releases/ #For example: #wget https://github.com/nghttp2/nghttp2/releases/download/v1.18.0/nghttp2-1.18.0.tar.gz #Verify the package after download (not covered here) tar -zxvf nghttp2-1.18.0.tar.gz cd nghttp2-1.18.0 export OPENSSL_CFLAGS="-I/usr/local/ssl/include" export OPENSSL_LIBS="-L/usr/local/ssl/lib -lssl -lcrypto" ./configure make sudo make install cd .. #Install latest apr #Get it from http://apr.apache.org/ #For example: #wget http://mirrors.whoishostingthis.com/apache/apr/apr-1.5.2.tar.gz #wget http://www.apache.org/dist/apr/apr-1.5.2.tar.gz.asc #Verify the package after download (not covered here but can be done with: gpg --verify apr-1.5.2.tar.gz.asc) tar -zxvf apr-1.5.2.tar.gz cd apr-1.5.2 ./configure make sudo make install cd .. #Install latest apr-util #Get it from http://apr.apache.org/ #For example: #wget http://mirrors.whoishostingthis.com/apache/apr/apr-util-1.5.4.tar.gz #wget http://www.apache.org/dist/apr/apr-util-1.5.4.tar.gz.asc #Verify the package after download (not covered here but can be done with: gpg --verify apr-util-1.5.4.tar.gz.asc) tar -zxvf apr-util-1.5.4.tar.gz cd apr-util-1.5.4 ./configure --with-apr=/usr/local/apr make sudo make install cd .. #Download and install apache #For example: #wget http://mirrors.whoishostingthis.com/apache/httpd/httpd-2.4.25.tar.gz #wget https://www.apache.org/dist/httpd/httpd-2.4.25.tar.gz.asc #Verify the package after download (not covered here but can be done with: gpg --verify httpd-2.4.25.tar.gz.asc) tar -zxvf httpd-2.4.25.tar.gz cd httpd-2.4.25 cp -r ../apr-1.5.2 srclib/apr cp -r ../apr-util-1.5.4 srclib/apr-util ./configure --with-ssl=/usr/local/ssl --with-pcre=/usr/bin/pcre-config --enable-unique-id --enable-ssl --enable-so --with-included-apr --enable-http2 make sudo make install cd ..

After this you need to add the /usr/local/lib/ and /usr/local/ssl/lib directories to the LD_LIBRARY_PATH. This can be set by either setting the LD_LIBRARY_PATH variable for the user, or by editing the /usr/local/apache2/bin/envvars script:

if test "x$LD_LIBRARY_PATH" != "x" ; then LD_LIBRARY_PATH="/usr/local/apache2/lib:/usr/local/lib/:/usr/local/ssl/lib:$LD_LIBRARY_PATH" else LD_LIBRARY_PATH="/usr/local/apache2/lib:/usr/local/lib:/usr/local/ssl/lib" fi

Next up you need to enable HTTP/2. This involved adding the following line to your apache config:

LoadModule http2_module modules/mod_http2.so

You also might want to add some debug for this module:

<IfModule http2_module> LogLevel http2:info </IfModule>

And finally, turn on the HTTP/2 protocol:

#Enable HTTP/2 support Protocols h2 http/1.1

After this stop and restart your apache (not just a graceful restart) using the apachectl script rather than just the httpd command so that the above env variables are picked up:

/usr/local/apache2/bin/apachectl -k stop

Note if you are running apache from a previous installation which was not in /usr/local/apache2 then you will need to use that stop command to stop it. Keep checking "ps" to ensure https is fully stopped running:

ps -ef | grep httpd | grep -v grep

Once it's fully down start it up again, you can start it up again:

/usr/local/apache2/bin/apachectl -k start

If all has gone well then you should see something like the following in your main error log file:

[Wed Jan 04 18:12:07.003271 2016] [http2:info] [pid 12345:tid 123456789012345] mod_http2 (v1.8.3, nghttp2 1.18.0), initializing... [Wed Jan 04 18:12:07.004910 2016] [mpm_event:notice] [pid 12345:tid 123456789012345] AH00489: Apache/2.4.25 (Unix) OpenSSL/1.0.2j configured -- resuming normal operations

If that works then you're looking good and can test a request from Chrome, by opening developer tools, adding protocol and making a request. It should hopefully look like this:

While Chrome Developer Tools does show HTTP/2 status, I have heard that it doesn't truly measure the performance boast given to HTTP/2 properly in the network tab. So better to measure the whole time, or perhaps use a tool like webpagetest.org to see any end to end improvement.

Note that the mod_http2 module is changing quite a bit (thanks to the awesome work of Stefan Eissing on mod_h[ttp]2 and Tatsuhiro Tsujikawa on the underlying nghttp2 library it uses). So you may want to install the latest version, even before the next version of Apache comes out. For example since Apache 2.4.25 (which includes mod_http2 1.8.3) there have been a few other releases with bug fixes. To install the latest mod_http2 from source follow these instructions:

#Download and install mod_http2 outside of a regular Apache release #Latest version is here: https://github.com/icing/mod_h2/releases/ wget https://github.com/icing/mod_h2/releases/download/v1.8.9/mod_http2-1.8.9.tar.gz tar -zxvf mod_http2-1.8.9.tar.gz cd mod_http2-1.8.9 ./configure --with-apxs=/usr/local/apache2/bin/apxs make sudo make install


Browser support is actually very strong, and the HTTP/2 is an upgrade request of HTTP/1.1 so those browsers that do not support it will continue to use HTTP/1.1 without issue.

Web server support is a bit behind the browsers. Apache added support for HTTP/2 from 2.4.17 and even then they state it's experimental at present. Similarly Ngingx has release 1.9.5 with HTTP/2 support, though again in experimental (Scott Helme has a similar blog entry to this one on how to install HTTP/2 on Nginx). Despite the experimental tag, these do seem fairly stable from the feedback online.

NodeJS had a problem with the upgrade header that some HTTP/2 servers send (including Apache from 2.4.18 onwards), which could cause some problems). I noticed this after upgrading to HTTP/2 and UptimeRobot stopped working for example as they use NodeJS (Update 9-April-2016: Fixed now!). As Node is fairly popular you may notice other issues like this for those running older versions (prior to version 4).

The Downsides

The main downside at present is the lack of support in production stable versions on the web server side. It is not yet recommended to run this on a production server. So far I've been running it on this blog with almost no issues - the one Node issue noted above is the main thing for now and that's a problem with Node rather than Apache - but I'd still advise caution before commercial businesses upgrade their own servers. Saying that using a third party CDN like Cloudflare may be an option and in fact they may already have upgraded you without your noticing!

As mentioned above HTTP/2 also requires HTTPS to work in the browsers, and more than that, some browsers also require good HTTPS config to use HTTP/2 - but really why would you not want to ensure you have good HTTPS config if you're proficient enough to get HTTP/2 up and running!. Run your site through SSLLabs HTTPS Testing tool before you upgrade to HTTP/2 and see also my tips on securing your HTTPS set-up.

And finally support in other tools for HTTP/2 is still being implemented. Cloudflare have an excellent list of resources for testing HTTP/2, but some of your regular tools (e.g. Chrome Developer Tools), may not be reporting accurate statistics at present.


HTTP/2 is an exciting new version of the main way our browsers talk to web servers. There are huge performance gains here. This website is very simple, with few resources, but even that has seen a speed improvement of 15%. This will be larger for more complex sites, and also over lower latency networks (e.g. browsing on mobile phones). At the moment I would not quite recommend installing on your production servers, but it's not far off and soon will be ready for the mainstream. Many big tech companies (e.g Google) are already on HTTP/2 and others (e.g. Facebook) are on the older SPDY protocol so will surely not be far behind. As I keep stating, performance is key in this world and HTTP/2 gives us a good jump up on that.

Some of the CDNs are offering HTTP/2 as part of their package (e.g. Cloudflare have excellent HTTP/2 support and are far and away the biggest implementers of HTTP/2 at the time of writing). If you really want HTTP/2 on your website you could do a lot worse than looking at them`for a hassle free set up.


I've written a follow up blog on HTTP/2 Server Push, which I've started using on this site as an experiment.

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