Contents

Introduction

While there exists good services for cloud-based load testing of Web sites (like in Visual Studio Team Services), sometimes there is a need for more lightweight and flexible solution.

In my case, I wanted to create load towards an Azure Event Hub to benchmark an IoT solution where the Event Hub handles the data ingestion to the cloud. Additionally, I wanted to generate the load with varying payload so that I could track in the downstream services how individual messages got handled.

For this purpose, there is an HTTP benchmarking tool called wrk that supports executing a LuaJIT script to modify the requests.

In this post, I’ll describe how I used wrk within a docker container and how I run it in Azure in a scalable and cost-efficient way.

Single instance locally

The sources of the image I used can be found here. Basic usage locally is:

docker pull vjrantal/wrk-with-online-script
docker run -e TARGET_URL=https://google.com vjrantal/wrk-with-online-script

As the name of the image indicate, in addition to running wrk, there is support for pointing wrk to a script hosted online. An example of such run below:

docker run -e SCRIPT_URL=https://gist.githubusercontent.com/vjrantal/113fa910444130d2d6431cdc84e6f80e/raw/0f67559a620647d6842c579b362a139a6b338cb1/script.lua -e TARGET_URL=https://google.com vjrantal/wrk-with-online-script

The benefit of pulling the script online versus passing it to the container as a file is that with the online approach, there is no need to mount any storage to the containers.

Scaling it up in Azure

There are several options to run containers in the cloud, but for this purpose, Azure Container Instances (ACI) works really well.

Running the container can be done using the azure-cli with a command like:

az container create -g MyResourceGroup --name wrk-with-online-script --image vjrantal/wrk-with-online-script -e TARGET_URL=https://google.com

Logs can be seen with:

az container logs -g MyResourceGroup --name wrk-with-online-script

And the container can be deleted with:

az container delete -g MyResourceGroup --name wrk-with-online-script

With a simple Python/Bash script, one can create multiple containers in wanted regions. The benefit over, for example, virtual machines is that the containers start in seconds and due to the per-second billing, you end up paying only for how long your load generator runs.

End to end example

As mentioned in the introduction, I used the described approach to generate load to an Event Hub. You can find the necessary steps and scripts from https://github.com/vjrantal/event-hub-loader and the repository also contains a Travis CI configuration that runs the load generator using a configurable amount of containers. Every CI run generates more than million messages with a running counter as the JSON payload. This all happens within minutes and can be considered a relatively cheap approach to generate load.