Open sourcing our NGINX HTTP/2 + SPDY code

by John Graham-Cumming.

In December, we released HTTP/2 support for all customers and on April 28 we released HTTP/2 Server Push support as well.

The release of HTTP/2 by CloudFlare had a huge impact on the number of sites supporting and using the protocol. Today, 50% of sites that use HTTP/2 are served via CloudFlare.

CC BY 2.0 image by JD Hancock

When we released HTTP/2 support we decided not to deprecate SPDY immediately because it was still in widespread use and we promised to open source our modifications to NGINX as it was not possible to support both SPDY and HTTP/2 together with the standard release of NGINX.

We've extracted our changes and they are available as a patch here. This patch should build cleanly against NGINX 1.9.7.

The patch means that NGINX can be built with both --with-http_v2_module and --with-http_spdy_module. And it will accept both the spdy and http2 keywords to the listen directive.

To configure both HTTP/2 and SPDY in NGINX you'll need to run:

./configure --with-http_spdy_module --with-http_v2_module --with-http_ssl_module

Note that you need SSL support for both SPDY and HTTP/2.

Then it will be possible to configure an NGINX server to support both HTTP/2 and SPDY on the same port as follows:

server {
        listen       443 ssl spdy http2;

        ssl_certificate      cert.pem;
        ssl_certificate_key  cert.key;

        location / {
            root   html;
            index  index.html index.htm;

Our patch uses ALPN and NPN to advertise the availability of the two protocols. To test that the two protocols are being advertised you can use the OpenSSL client as follows (sending an empty ALPN/NPN extension in the ClientHello causes the server to return a list of available protocols).

openssl s_client -connect -nextprotoneg ''
Protocols advertised by server: h2, spdy/3.1, http/1.1

Many other tools for testing and debugging HTTP/2 connections can be found here.

The patch puts HTTP/2 before SPDY/3.1 and will prefer HTTP/2 over SPDY/3.1. If a web browser offers both, HTTP/2 will be preferred and used for the connection.

We continue to support SPDY and HTTP/2 across all CloudFlare sites and will keep an eye on the percentage of connections that use SPDY before making a decision on its eventual deprecation.

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