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Zalando end-to-end load tester

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Zalando end-to-end load tester

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A command-line tool for orchestrating the deployment of Locust in Kubernetes.

Use it in conjunction with Transformer to run large-scale end-to-end load testing of your website.



Install using pip:

pip install zelt


Example HAR files, locustfile, and manifests are included in the examples/ directory, try them out.

N.B The cluster to deploy to is determined by your currently configured context. Ensure you are using the correct cluster before using Zelt.

Locustfile as input

Zelt can deploy Locust with a locustfile to a cluster:

zelt from-locustfile PATH_TO_LOCUSTFILE --manifests PATH_TO_MANIFESTS

HAR files(s) as input

Zelt can transform HAR file(s) into a locustfile and deploy it along with Locust to a cluster:

zelt from-har PATH_TO_HAR_FILES --manifests PATH_TO_MANIFESTS

N.B This requires Transformer to be installed. For more information about Transformer, please refer to Transformer’s documentation.

Rescale a deployment

Zelt can rescale the number of workers in a deployment it has made to a cluster:

zelt rescale NUMBER_OF_WORKERS --manifests PATH_TO_MANIFESTS

Delete a deployment

Zelt can delete deployments it has made from a cluster:

zelt delete --manifests PATH_TO_MANIFESTS

Run Locust locally

Zelt can also run Locust locally by providing the --local/-l flag to either the from-har or from-locustfile command e.g.:

zelt from-locustfile PATH_TO_LOCUSTFILE --local

Use S3 for locustfile storage

By default, Zelt uses a ConfigMap for storing the locustfile. ConfigMaps have a file-size limitation of ~2MB. If your locustfile is larger than this then you can use an S3 bucket for locustfile storage.

To do so, add the following parameters to your Zelt command:

  • --storage s3: Switch to S3 storage
  • --s3-bucket: The name of your S3 bucket
  • --s3-key: The name of the file as stored in S3

N.B. Zelt will not create the S3 bucket for you.

N.B. Make sure to update your deployment manifest(s) to download the locustfile file from S3 instead of loading from the ConfigMap volume mount.

Use a configuration file for Zelt options

An alternative to specifying Zelt’s options on the command-line is to use a configuration file, for example:

zelt from-har --config examples/config/config.yaml

N.B. The configuration file’s keys are the same as the command-line option names but without the double dash (--).


Take a look at our documentation for more details.


Please read for details on our process for submitting pull requests to us, and please ensure you follow the


We use SemVer for versioning.


See also the list of contributors who participated in this project.


This project is licensed under the MIT License - see the LICENSE file for details

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