experiment-template.md

Experiment Parameter Templating

Parameters provides Kallisti users with the ability to templatize your chaos experiments and trials. You can define various key-value pairs in parameters inside chaos experiments and trials which would be interpolated into step defined under pre_steps, steps and post_steps.

In where clause of a step definition, you can refer to a template parameter with the parameter_name. This will be interpolated with parameter_value during trial execution. See sample below:

{
  "name": "some experiment name",
  "description": "detailed description of the experiment",
  "parameters": {
    "parameter_name": "parameter_value"
  },
  "steps": [ 
    { "step": "HTTP health check",
      "do" : "cm.http_probe",
      "where": { "url" : "{{ parameter_name }}" }
    }
  ]
}

Kallisti will search the parameters field in experiment or trial definition for the value with key parameter_name, and replace the template parameter reference (i.e. {{ parameter_name}} occurrences) with the value found. This gives the ability to maintain configuration separate from the step definitions and reuse it across steps.

Rules

• The parameter_name allows any combination of alphanumeric characters and underscore ("_").
• You cannot have spaces or punctuation characters in parameter_name.
• You can provide parameters field in either experiment, schedule, trial definition or all of them.
• In the case where parameters are provided at multiple places (experiment and/or schedule and/or trial) then the parameters used for trial execution will be in the mentioned order of precedence: trial over schedule over experiment.
  You can see some sample use cases below.
• If a parameter_name is used in the experiment body but not defined under the parameters object in both experiment json and trial json then the trial will be marked with Invalid status. See Trial Status for more details.

Sample Use Cases

Use case 1: Providing parameters in experiment

The example above shows experiment definition contains template parameters and will be interpolated to the parameters value during trial execution on the right side

Use case 2: Providing parameters in both experiment and trial

The example shows the interpolation effect if you provide the parameters field in trial definition. The value of parameters provided in experiment definition will be overwritten.

Note:

This feature currently only support interpolation of String type parameters in experiment step. We are working on providing the complete support for other types of step parameters.