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How to write a Litmusbook

The Litmus framework adopts a user-friendly structure in which addition of new experiments (tests) can be an easy exercise without too-much logic building. However, it does involve packaging the test in the standard litmusbook structure and reusing/creating simple ansible task files and playbooks. Here is a quick refresher on the moving parts & basic process flow in a Litmus experiment:

  • The deployable/executable artifact associated with the Litmus experiment is called Litmusbook. This is a Kubernetes Job (run_litmus_test.yml)

  • The Litmusbook runs & manages the “ansible-runner” container

  • The ansible-runner container executes the test playbook (test.yml) as the entrypoint function.

  • The test playbook executes several locally defined tasks as well as those in (statically imported) LitmusLib utils/taskfiles (viz. common, funclib, chaoslib)

  • The LitmusLib utils may utilize specific “third-party” tools (deployed as Kubernetes deployments or daemonsets) to perform specific functions

  • Test result is updated in a dedicated Kubernetes custom resource called litmusresult

The subsequent sections will explain how an interested user/developer can approach the creation of a new Litmus Experiment. An intermediate-level knowledge of ansible (& of course, Kubernetes) is expected.