Y U No Support SPDY Yet?

#fasterapp #ado #interop Mega-sites like Twitter and popular browsers are all moving to support SPDY – but there’s one small glitch in the game plan…

SPDY is gaining momentum as “big” sites begin to enable support for the would-be HTTP 2.0 protocol of choice.

Most recently Twitter announced its support for SPDY:

Twitter has embraced Google’s vision of a faster web and is now serving webpages over the SPDY protocol to browsers that support it.

SPDY is still only available for about 40 percent of desktop users. But with large services like Twitter throwing their weight behind it, SPDY may well start to take the web by storm — the more websites that embrace SPDY the more likely it is that other browsers will add support for the faster protocol.

-- Twitter Catches the ‘SPDY’ Train

But even with existing support from Google (where the protocol originated) and Amazon, there’s a speed bump on the road to fast for SPDY:

There is not yet any spdy support for the images on the Akamai CDN that twitter uses, and that's obviously a big part of performance. But still real deployed users of this are Twitter, Google Web, Firefox, Chrome, Silk, node etc.. this really has momentum because it solves the right problems.

Big pieces still left are a popular CDN, open standardization, a httpload balancing appliance like F5 or citrix. And the wind is blowing the right way on all of those things. This is happening very fast.

-- Twitter, SPDY, and Firefox 

The “big pieces” missing theme is one that’s familiar at this point; many folks are citing the lack of SPDY support at various infrastructure layers (in particular the application delivery tier and load balancing services) as an impediment embracing what is certainly the early frontrunner in the HTTP 2.0 War. While mod_spdy may address the basic requirement to support SPDY at the web server infrastructure layer, mod_spdy does not (and really can not) address the lack of support in the rest of the infrastructure.

Like the IPv4 to IPv6 transition, the move to support SPDY is transitory in nature and counts on HTTP 2.0 adopting SPDY as part of its overhaul of the aging HTTP protocol. Thus, infrastructure must maintain a dual SPDY-HTTP stack, much in the same way it must support both IPv4 and IPv6 until adoption is complete - or a firm cutover date is arrived at (unlikely).

U No Support SPDY because SPDY Support is No Easy

The use of SPDY is transparent to the user. But for IT the process of supporting SPDY is no simple task. To understand the impact on infrastructure first take a look at the typical steps a browser uses to switch to SPDY from HTTP:

  • The first request to a server is sent over HTTP
  • The server-side end-point (server or application delivery service), when it supports SPDY, can reply with an HTTP header 'Alternative-Protocols: 443:npn-spdy/2', indicating that the content can also be retrieved on this server on port 443, and on that port there is a TLS 1.2 endpoint that understands NPN and SPDY can be negotiated
  • Alternatively the server can just 301 redirect the user to an https end-point.
  • The client starts a TLS connection to the port described and when the server-side end-point indicates SPDY as part of the TLS NPN extension, it will use SPDY on that connection.

What this means is that infrastructure must be updated not just to handle SPDY – which has some unique behavior in its bi-directional messaging model – but also TLS 1.2 and NPN (Next Protocol Negotiation). This is no trivial task, mind you, and it’s not only relevant to infrastructure, it’s relevant to site administrators who want to enable SPDY support. Doing so has several pre-requisites that will make the task a challenging one, including supporting TLS 1.2 and the NPN extension and careful attention to links served, which must use HTTPS instead of HTTP.

While you technically can force SPDY to be used without TLS, this is not something a typical user will (or in the case of many mobile platforms can) attempt. For testing purposes, running SPDY without TLS can be beneficial, but for general deployment? SSL Everywhere will become a reality. Doing so without negatively impacting performance,  however, is going to be a challenge.

Establishing a secure SSL connection requires 15x more processing power on the server than on the client.

-- THC SSL DOS Tool Released 

The need to support secure connections becomes a big issue for sites desiring to support both HTTP and HTTPS without forcing SSL everywhere on every user, because there must be a way to rewrite links from HTTP to HTTPS (or vice-versa) without incurring a huge performance penalty. Network-scripting provides a solution to this quandary, with many options available – all carrying varying performance penalties from minimal to unacceptable.


Basically, there are a whole lot of pros to SPDY – and a whole lot of cons. Expect to see more sites – particularly social media focused sites like Facebook – continue to jump on the SPDY bandwagon. HTTP was not designed to support the real-time interaction inherent in social media today, and its bursty, synchronous nature often hinders the user-experience. SPDY has shown the highest benefits to just such sites – highly interactive applications with lots of small object transfers – so we anticipate a high rate of early adoption amongst those who depend on such applications to support its business model.

Supporting SPDY will be much easier for organizations that take advantage of an intelligent intermediary. Such solutions will be able to provide support for both HTTP and SPDY simultaneously – including all the pre-requisite capabilities. Using an intermediary application delivery platform further alleviates the need to attempt to deploy pre-production quality modules on critical application server infrastructure, and reduces the burden on operations to manage certificate sprawl (and all the associated costs that go along with that).

SPDY is likely to continue to gain more and more momentum, especially in the mobile device community. Unless Microsoft’s Speed+Mobility offers a compelling reason it should ascend to the top of the HTTP 2.0 stack over SPDY, it’s likely that supporting SPDY will become a “must do” instead of “might do” sooner rather than later.

Published May 07, 2012
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