Introduction

This Guide describes how the OnDemand Agents work for Apica LoadTest (ALT), and tips to not overload them.

Locations

Location Map	OnDemand Agent Locations
When you set up a load test, you choose from a set of locations, from where you want to run your load test:	Each location has a number of available OnDemand Agents.

OnDemand Agents

On the following link you can find up-to-date information about locations and agents:

ALT Agent Global Locations with IPs

The current number of available agents per location:

How Customer Jobs are Allocated

Each OnDemand Agent has a limit of 500-1,000 Virtual Users, depending on the location and contract.

When a customer runs a load test job, one or more agents are:

• Reserved for that customer only

  • For each location

  • For the duration of the job

  • For a maximum of 500 Virtual Users (VU) per Agent

• The allocation takes place before the jobs start.

• These agents are not available for any other customers or jobs for the duration of the test.

Example:

A customer wants to run a load test of 1,800 VU’s from 2 locations. The system will then allocate 2 agents in each location, and each agent will run 450 VU’s.

When using Performance Test Scenarios and several tests, each test/Job is handled separately.

Performance of a Load test Agent

As before, each Agent is allocated up to 500 VU’s, but the CPU load on the Agents can vary a lot depending on the script:

Each of these conditions calls for More/Higher CPUs:

• The number of calls per “page”

  • Higher calls

• If calls are made in “parallel” or “serial”

  • Parallel Calls

• The think time (pause) between each “page”

  • Shorter Think Times

• The response times of the called resources

  • Shorter Response Time

Can you see if an Agent is overloaded?

1. Compare Response Times

The typical symptom of an overloaded Agent is that the total duration of a test iteration (“loop time”) is clearly longer than the sum of the “page times”.

This is because not all execution time is included in the page times. For instance, SSL handshakes, HTTP handshakes, and garbage collection.

• When the CPU of the Agent is overused, these processes may take significant time.

Example:

On the test “Overview” tab look for this

Compare to this:

In this example, there was no difference, so the Agent worked fine!

Looking in the detailed result file

Once a job is finished, you can download the detailed result file and analyze it. In the “Jobs” view, click the download icon for the job you’re interested in.

This will get you an xxx.prxres file. Put the file in the ZebraTester/MyTests folder.

Open the file in the ZebraTester UI/Project Navigator:

Then click the magnifying glass next to the Load Test name:

Then select the Diagram: Load Generator Performance:

Finally, look at the CPU Usage graph:

In this example, the usage is very low, so we’re fine!

2. Leverage SSL Cache Efficiencies

You can check for this in the result file (see the previous section), by selecting Diagram: SSL Cache Efficiency. In the example below, it shows that a new SSL handshake was performed for each and every request. This can be CPU intensive.

Also, look at the Results per Page | URL (Details) view. Compare the numbers in the Av SSL/TLS column with the Av Time column. In the example below, about 10% of the time is spent on SSL.