Open-Source Apache Traffic Server 4 Accelerates the Web

The Apache Traffic Server 4 caching proxy server release improves Web performance and stability.

The open-source Apache Traffic Server is hitting a major milestone with the release of a new version and a new road map for future development. The Apache Traffic Server was originally donated to the Apache Software Foundation by Yahoo and is a caching proxy server that can speed up the delivery of Web server content. A caching proxy server stores copies of frequently accessed content, making it more rapidly accessible to users.

While Yahoo was the creator of the Traffic Server effort, Leif Hedstrom, vice president of the Apache Traffic Server (ATS) project, told eWEEK that currently, very little in the way of contributions are coming from Yahoo, at least for now.

"The reason is that Yahoo decided to pursue other software alternatives a few years ago," Hedstrom said. "The good news is that Yahoo recently announced that they will move their software development effort back to Apache Traffic Server again, and will contribute everything back to Apache."

Hedstrom noted that the large users of ATS are also among the project's biggest contributors. ATS users include Comcast, Akamai, GoDaddy and LinkedIn, among others.


Among the big improvements in the ATS 4.0 release are enhancements that improve performance.

"For most systems, there's not a noticeable performance increase," Hedstrom said. "On systems with two or more NUMA sockets, the performance improvements can be quite dramatic; we've measured two to three times the throughput in some cases."

One of the new features that can improve performance significantly is the ability to assign URL sets (address locations) to specific disk volumes. Hedstrom explained that, for example, if you have a subset of URLs that you know are hotter (or more important) than others, assigning those to a fast solid-state disk can yield significant performance improvements. Additionally, ATS users can now mix SSDs and rotational disks efficiently.

"There's also an experimental feature that lets ATS migrate objects [URLs] automatically between rotational disks and SSD disks," Hedstrom said. "This is still work in progress, which is why it is still in the experimental state."

The experimental migration feature is, however, already actively used by Asian Web giant Alibaba Taobao, the vendor that developed the feature.

"We have also started a foundation of making performance on very high connection servers better," Hedstrom said. "This will be completed during the 4.x release cycles, and the goal here is to scale to millions of concurrent connections with little CPU overhead."

In order to improve the stability of ATS, there is a new feature called HTTP transaction buffering control. Hedstrom explained that feature is about making sure that ATS does not consume boundless memory when proxying requests from clients to the origin server.

Road Map

With the ATS 4.0 release, the project is now embracing a new release process that will serve to accelerate innovation and development.

"From now on, all releases are stable and production-ready," Hedstrom said. "As such, the deltas between minor releases are much smaller, and always compatible, making upgrades safer and easier."

In terms of features in upcoming ATS releases, key areas that Hedstrom would like to see improve include Domain Name System (DNS) and load balancing. The team at Alibaba Taobao is also working feverishly on improvements to cache clustering, which promises significant improvements to the ATS distributed cache clustering solution, he added.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.