1. Technical Field
The present invention relates generally to testing a request-response service using live connection traffic. One such request-response service involves high-performance, fault-tolerant HTTP, streaming media and applications delivery over a content delivery network (CDN).
2. Description of the Related Art
It is well-known to deliver HTTP and streaming media using a content delivery network (CDN). A CDN is a self-organizing network of geographically distributed content delivery nodes that are arranged for efficient delivery of digital content (e.g., Web content, streaming media and applications) on behalf of third party content providers. A request from a requesting end user for given content is directed to a “best” replica, where “best” usually means that the item is served to the client quickly compared to the time it would take to fetch it from the content provider origin server. An entity that provides a CDN is sometimes referred to as a content delivery network service provider or CDNSP.
Typically, a CDN is implemented as a combination of a content delivery infrastructure, a request-routing mechanism, and a distribution infrastructure. The content delivery infrastructure usually comprises a set of “surrogate” origin servers that are located at strategic locations (e.g., Internet network access points, Internet Points of Presence, and the like) for delivering copies of content to requesting end users. The request-routing mechanism allocates servers in the content delivery infrastructure to requesting clients in a way that, for web content delivery, minimizes a given client's response time and, for streaming media delivery, provides for the highest quality. The distribution infrastructure consists of on-demand or push-based mechanisms that move content from the origin server to the surrogates. An effective CDN serves frequently-accessed content from a surrogate that is optimal for a given requesting client. In a typical CDN, a single service provider operates the request-routers, the surrogates, and the content distributors. In addition, that service provider establishes business relationships with content publishers and acts on behalf of their origin server sites to provide a distributed delivery system. A well-known commercial CDN service that provides web content and media streaming is provided by Akamai Technologies, Inc. of Cambridge, Mass.
CDNSPs may use content modification to tag content provider content for delivery. Content modification enables a content provider to take direct control over request-routing without the need for specific switching devices or directory services between the requesting clients and the origin server. Typically, content objects are made up of a basic structure that includes references to additional, embedded content objects. Most web pages, for example, consist of an HTML document that contains plain text together with some embedded objects, such as .gif or .jpg images. The embedded objects are referenced using embedded HTML directives. A similar scheme is used for some types of streaming content which, for example, may be embedded within an SMIL document. Embedded HTML or SMIL directives tell the client to fetch embedded objects from the origin server. Using a CDN content modification scheme, a content provider can modify references to embedded objects so that the client is told to fetch an embedded object from the best surrogate (instead of from the origin server).
In operation, when a client makes a request for an object that is being served from the CDN, an optimal or “best” edge-based content server is identified. The client browser then makes a request for the content from that server. When the requested object is not available from the identified server, the object may be retrieved from another CDN content server or, failing that, from the origin server.
A well-managed content delivery network implements frequent upgrades to its production software, e.g., the software used to provide HTTP content delivery from its edge-based content servers. Thus, for example, as new content or “edge” server functionalities are added to the network, they need to be tested, debugged, rewritten and, ultimately, deployed into production across the network as a whole. An ongoing challenge is testing such new software is the inability to reproduce real-world workload on new versions of the software short of deploying them in the field. While testing a CDN server with real-world traffic (a “live load test”) would be desirable, it has not been possible to do so without having the CDN server interact with the outside world. This interaction may cause significant problems if the version under live test has bugs or otherwise interferes with conventional server functions. Additionally, when field-deployment is used, there is no convenient mechanism for checking if a new version of the software under test produces equivalent output to the old version, namely, the production version.
Generally, there are a number of known approaches to testing software. Regression testing refers to the technique of constructing test cases and executing the software against those cases. Regression testing, while effective in avoiding repeat of bugs, is labor-intensive and thus costly. Stress or “load” testing refers to the technique of simulating the working environment of the software using a testbed or equivalent architecture. While stress/load testing is useful in evaluating system limits, finding representative workloads to use for the test is always difficult. Trace-based testing refers to the technique of playing back to the software under test a trace of activity obtained from a production version. This technique, although generally useful, may lead to inaccurate conclusions as, in some applications (like a CDN caching server), traces go stale very quickly and/or do not include information that might be needed to evaluate the new version effectively. Field-deployment testing, as its name suggests, refers to the technique of testing a version of the software with a real-world workload. As noted above, when field-deployment is used, there is no convenient way of isolating the software under test from interacting with real users and customers, and there is no mechanism for checking if a new version of the software under test produces equivalent output to the old version, namely, the production version. Error detection is hard, and debugging is difficult because there is limited information capture and the developer is often unable to deploy instrumented code. In addition, during live field-testing, the developer is not able to destructively test the code, i.e., to make the software less robust (e.g., letting it crash) in the face of problems instead of patching over them, in order to assist in tracking down problems.
It would be desirable to be able to provide a way to test IP-networking-based servers (either software, hardware, or some combination thereof) with live traffic and to compare the results of these tests with currently running CDN traffic. Such a method also could be used to test network-based servers before their actual deployment. The present invention addresses this need in the art.