Run a load test using Zelt

This guide will take you through:

  • Setting up Kubernetes
  • Defining your load test
  • Using Zelt to deploy Locust
  • Running your load test

Install Zelt

To get started, first install Zelt from PyPI:

pip install zelt

Install minikube

For the purpose of this guide we will use a local instance of Kubernetes called minikube. Note that this setup will not allow you to generate any significant load. We recommended using a hosted Kubernetes solution when you want to execute large-scale load tests.

If you already have a hosted Kubernetes, e.g. EKS, then skip this section.

  1. Download and install minikube

  2. Enable Ingress:
    minikube addons enable ingress
  3. Configure a hostname for minikube:
    echo `minikube ip` zelt.minikube | sudo tee -a /etc/hosts

Create a scenario

In order to run a load test, we need to create a load test scenario. If you already have a locustfile representing a load test scenario, then skip this section.

  1. Chose your target i.e the application you want to test
  2. Follow this guide to create a HAR file for the scenario
  3. Save the HAR file locally, we will refer to it as PATH_TO_HAR_FILE in this guide

Determine deployment type

Zelt can deploy Locust in either combined (standalone) or distributed mode. The decision for which mode to use depends on how much load you wish to generate and the hardware available to you.

In combined mode, Locust can generate ~500 users (per CPU core). This equivalent to running Locust locally.

In distributed mode, Locust uses workers to generate the load. Therefore, the number of users can be calculated as the number of workers you deploy multiplied by 500. For example, if you wanted to have 1000 users you would deploy Locust in distributed mode with 2 workers.

Keep in mind that since the amount of users is CPU-bound, the hardware of each worker will affect the amount of load generated.

If using an AWS-hosted Kubernetes, take a look at this table for a detailed breakdown of how much load can be generated by different instance types.

Prepare manifests

Kubernetes uses manifest files to define what to deploy. Example manifest files for both combined and distributed deployment are available in Zelt’s source code.

For the purpose of this guide, we will use the distributed manifests. These consist of:

  • controller-deployment.yaml that defines the Locust controller
  • worker-deployment.yaml that defines the Locust worker(s)
  • namespace.yaml that defines the Kubernetes namespace to deploy to
  • service.yaml that defines the Kubernetes service to create
  • ingress.yaml that defines the Kubernetes ingress to create

Note

Currently Zelt’s support is limited to the above Kubernetes resource types, as well as custom resources. Please note that Zelt will deploy a custom resource only if its custom resource definition is already deployed in the cluster, and only if the scope of the resource is limited to a namespace.

1. Download them and save them locally, we will refer to their location as PATH_TO_MANIFESTS in this guide.

N.B. The hostname specified when configuring minikube must match that defined in the ingress.yaml file.

Deploy to Kubernetes

Once you have a load test scenario, you can use Zelt to deploy it to Kubernetes.

First, ensure you are logged in to the correct cluster e.g.:

kubectl config use-context minikube

From HAR

Zelt will use Transformer to convert your HAR file to a locustfile before deploying it to Kubernetes.

zelt from-har PATH_TO_HAR_FILE --manifests PATH_TO_MANIFESTS

From locustfile

If you already have a locustfile, then run the following command instead:

zelt from-locustfile PATH_TO_LOCUSTFILE --manifests PATH_TO_MANIFESTS

Both of these commands will:

  1. Create a Namespace called zelt (subsequent items will be created there)
  2. Deploy 1 Locust controller and 2 workers
  3. Create a Service for communication between the controller and workers
  4. Expose the Locust UI at http://zelt.minikube using Ingress

Run the load test

In order to actually run the load test, we will use the Locust dashboard:

  1. In your browser, navigate to http://zelt.minikube
  2. Enter a desired number of users to simulate
  3. Enter the desired ramp-up speed
  4. Click Start swarming

Refer to Locust’s documentation for more information on how to run/stop/report your load test.

Rescale your deployment

You can use Zelt to increase/descrease the number of Locust workers that are available to generate load without needing to redeploy.

For example, to reduce the number of workers to 1 simply run:

zelt rescale 1 -m PATH_TO_MANIFESTS

N.B. If a load test is currently running then increasing the number of worker pods will not immediately increase the amount of load being generated. The load test must be restarted through the Locust UI. Decreasing the number of workers will decrease the amount of load being generated immediately.

Delete your deployment

Once your load test has completed, you can use Zelt to delete the Locust deployment from Kubernetes.

zelt delete -m PATH_TO_MANIFESTS

N.B. Make sure you have downloaded your Locust reports if you want them before doing this or they will be deleted!