Addanc

Project Status

Download

Documentation

SourceForge Project Support

Addanc is a distributed, scalable system for stress- or load-testing Web applications. Addanc is most useful for testing complex systems consisting of multiple "moving parts" with a web GUI.

Addanc focuses on the arrival rate of ”service requests”, rather than generating a server load based on a fixed number of clients. Addanc clients arrive at a specific rate and execute a set of HTTP/HTTPS GET and/or POST transactions representing the “service request.”

Addanc supports the following features:

Definable arrival rates
Unlimited number of clients
Scheduled tests
HTTP and HTTPS support
Cookie support
Redirection support
Configurable test durations
Ability to allow client scripts to complete at test termination
XML based scripts
Configurable inter-page wait times
Real-time monitoring of internal queues
Jabber support for distributed component command, control, and monitoring
Instrumentation of page times, transaction connect times, send and receive times, send and receive byte counts
MySQL and file support for recording instrumentation data
Configurable page and transaction ids
Distributed, scalable architecture

The Addanc project is open-source, uses open-source components and is hosted on sourceforge.net. The Addanc team appreciates the support of the open source community and the project support services provided by SourceForge.

Why Addanc?

Addanc is different from most other web performance testing systems in that it focuses on testing a system via the arrival rate of new requests for services rather than a fixed number of clients. Members of the development team have used a number of testing tools that focus on delivering testing traffic from a fixed (or varying) number of clients. In these test environments, the number of clients is fixed and each client iterates through a script. The load generated by a client-oriented system is limited by the number of clients and the time it takes the system under test (SUT) to respond to all the requests in a client's script. Thus, the load generator and the SUT are tied together in a feedback loop. This becomes a non-linear system leading to unpredictable behavior that may be sensitive to initial conditions. At extremes of performance, which is where most testing is interesting, this feedback loop limits the test load and often causes positive feedback and wild swings in measured performance and loads. Even when not at extremes, testing systems based on a fixed number of clients are difficult to "tune" when attempting to test systems against transaction rate metrics. For example, it can be difficult to determine, except with trial and error, the number of clients required to generate a targeted transaction rate.

Addanc decouples the generation of test traffic from the "life" of a client. Addanc generates new clients at a specified rate. These clients then execute their assigned script and exist for as long as necessary to complete the script. When the arrival rate of new clients is well below the work capacity of a tested system, the number of clients will remain relatively fixed, with some variance due to the stochastic nature of servicing the requests. When the client arrival rate starts to exceed the work capacity of the SUT, the number of active clients will start (and usually continue) to rise. When the client arrival rate closely matches the work capacity of the SUT, the number of active clients will vary as the system deals with the work requests. Because Addanc clients are generated at a determined rate, it avoids "surging" or client synchronization that can occur in other systems due to resource queuing. By generating new clients based on arrival rate, Addanc also avoids the problem of starting a set of clients at the same time (which would result in synchronized demand as all clients step through their scripts at the same rate).

So, Addanc offers a better testing environment than fixed-client testing systems by more accurately simulating a "real world" environment where service demand and capacity are independent. By focusing on arrival rates, Addanc allows the tester to plan and develop tests that will reveal the behavior of the SUT under loads expected when deployed.

Addanc is most useful when testing complex applications consisting of several "moving parts" with a web-based front end. The stochastic nature of such systems can make client based tests difficult to plan and interpret. Consider a system involving multiple application servers, a database server, and a communication channel to a mainframe application. When testing such a system at the limits of its capacity using a fixed number of clients, small perturbations in mainframe service times or communication channel capacity may cause strong feedback to the testing system leading to wide swings in test load, measured performance, and measured throughput. Because Addanc continues to generate new requests for service, uncoupled from the SUT's ability to handle the requests, this feedback is avoided and true measures of performance and capacity may be obtained.

Addanc Components

An Addanc test system consists of number of cooperating and interacting components. These components communicate with each other using the Jabber protocol. Addanc components can exist on the same network or can be distributed across any number of networks, as long as they can all access a common jabber server. The Addanc Brick provides the basic testing functionality. Thus, increasing testing capacity is simply a matter of provisioning additional Bricks.

The basic Addanc components are:

Addanc Commander - The Commander is the basic command and monitoring interface for the Addanc Web Testing System. The Commander provides the basic ability to schedule tests, monitor the state and activity of Addanc Bricks, and to control the activity of Addanc Bricks. The commander uses wxPython to provide a portable GUI .
Addanc Brick - An Addanc Brick provides the basic testing functionality for the Addanc Web Testing System. A Brick generates simulated clients at a specified rate, executes the simulated client's script, and collects the instrumentation metrics. The total number of Bricks provisioned or allocated to the testing system defines the overall testing capacity of an Annanc Web Testing System.
Addanc Jabber Server - Basic command, control, and status information is transferred between Addanc components via the jabber protocol. To minimize latency issues, we recommend using a dedicated jabber server in the Addanc Web Testing System.

Addanc Prerequisites

Addanc uses a number of other open-source components. To successfully install and use Addanc you must download and install the following packages:

Python 2.3 - Addanc is written in Python and uses features that first appeared in Python 2.3.
Jabber - You will probably want to install a local copy of a jabber server for your Addanc system if you need GUI control of multiple bricks via the Addanc Commander.
M2Crypto - Addanc uses the M2Crypto Python (Version 0.11) wrapper for the OpenSSL functions. If you do not need HTTPS transaction support, you do not have to install M2Crypto. The Addanc Brick will function without the module.
OpenSSL - To successfully use Addanc with SSL/HHTPS tests, you must download the source tar-ball and (re)build OpenSSL with RC5, and IDEA support. (This is really a M2Crypto prerequisite.)
SWIG - M2Crypto uses the Simplified Wrapper and Interface Generator, SWIG (Version 1.3.17), to build wrappers for the OpenSSL functions.
wxPython - Addanc (specifically, the Addanc Commander) uses wxPython to provide a portable GUI across Windows and X11 systems.
MySQLdb - The Addanc Brick can be configured to store instrumentation information in a MySQL database. If you choose to enable this feature, you will need to install the MySQLdb package.

The Addanc installation process will automatically install the following packages:

ElementTree - Addanc uses Fredrik Lundh's ElementTree object to handle some (soon to be all) XML parsing and storing operations.
pyjabber - Addanc uses jabber to coordinate the activities of distributed components.

Addanc Mailing Lists

The Addanc team has established the following mailing lists:

addanc-user - For usage questions and discussions.
addanc-developer - For developer exchange of information, discussions and debates.
addanc-announce - For announcing new releases of Addanc.

Where does the name Addanc come from?

Addanc (also spelled Affanc, Avanc, or Abac) is a character from pre-Christian Welsh and Celtic mythology. Like many cultures, early Welsh and Celtic mythology includes a story about a worldwide flood or deluge. In the Celtic flood mythology, Addanc was a primordial god or faery, often characterized as a dragon, who created and rode (surfed) the crest of the great flood near his home on Llyon Llion, the Lake of Waves. The flood washed over the entire earth killing all inhabitants except the God/Hero Dwyvan, and his wife, the Goddess/Heroine Dwyvach, who escaped the flood in an ark.

In modern Wales, "Addanc" is used to describe any evil fresh water-dwelling spirit. The related term "Afanc" describes a beaver.

The Addanc development team relishes the image of a giant dragon surfing the crest of a large wave washing across the world destroying everything in its path. Now that's a stress test!

Page Updated: 2/9/2004