Parameterize your script for multiple environments

A CI/CD pipeline often runs the same script against different environments: a preview after a pull request, staging before a release, and sometimes production after deployment. If your script has a hardcoded URL, you need a separate script for each environment. Environment variables eliminate this problem. You define the target URL once as a variable and pass the value at runtime.

To parameterize your script, complete the following steps:

1. Open your k6 test script and replace any hardcoded URLs with __ENV.BASE_URL. For example, change:

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   const res = http.get('https://staging.example.com/api/health');

   to:

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   const res = http.get(`${__ENV.BASE_URL}/api/health`);

   __ENV is a k6 global object that provides access to environment variables passed with the -e / --env flag or set in the shell environment. For details, refer to Environment variables.

2. Run the script locally with the -e flag to pass the base URL:

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   k6 run -e BASE_URL=https://staging.example.com test.js

   Verify that the test runs successfully against the specified environment.

3. Add a default value check at the top of your script to catch missing variables early:

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   const BASE_URL = __ENV.BASE_URL;
   if (!BASE_URL) {
     throw new Error(
       'BASE_URL environment variable is required. Use: k6 run -e BASE_URL=https://... test.js'
     );
   }

   Without this check, a missing BASE_URL produces confusing HTTP errors instead of a clear message about the missing variable.

4. Test that the error message works by running without the -e flag:

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   k6 run test.js

   You should see the error message you defined. This confirms that the script fails fast when the required variable is missing.

Tip: You can parameterize more than just the URL. Use __ENV for any value that varies between environments, such as authentication tokens (__ENV.API_TOKEN). Keep secrets out of the script and inject them from your CI platform’s secret store.

In the next milestone, you add k6 as a step in your CI/CD pipeline.