Simulation hooks #

SimKube supports running arbitrary setup or cleanup scripts at a number of different points during the simulation process. The general method for configuring hooks is the same at each extension point: simply inject the following command into the Simulation custom resource:

- cmd: echo           # required
  args: ["foo"]       # required
  ignoreFailure: true # optional, will not abort the simulation on failure
  sendSim: true       # optional, will send the Simulation resource to the hook as JSON over stdin

Extension points #

There are four places where hooks can be injected:

preStartHooks #

Pre-start hooks run once before any other simulation setup; you can use these hooks to create additional namespaces, set up monitoring, etc.

postStopHooks #

Similarly, post-stop hooks run once after all simulation iterations have completed and after all other cleanup tasks are complete. They can be used to clean up any resources or do additional reporting on the simulation results (extracting logs from relevant pods, for example).

preRunHooks #

Pre-run hooks run before every iteration of the simulation, and can be used to re-create resources that should be "fresh" at the beginning of each iteration. They are the first thing the SimKube driver runs, before executing any other setup.

postRunHooks #

Lastly, post-run hooks run at the end of every simulation iteration, and can be used to clean up resources that might pollute future simulation iterations. They are the last thing the SimKube driver runs.

Injecting hooks #

If you are using skctl to run your simulation, you can provide a set of hooks via a YAML file similar to the following, using the --hooks CLI argument:

---
# Pre-start hooks execute before any simulation setup occurs
preStartHooks:
  - cmd: echo
    args: ["foo"]
# Pre-run hooks execute after setup but before the driver begins
preRunHooks:
  - cmd: echo
    args: ["bar"]
# Post-run hooks execute after the driver stops but before simulation cleanup
postRunHooks:
  - cmd: echo
    args: ["baz"]
# Post-stop hooks execute after all other simulation cleanup steps
postStopHooks:
  - cmd: echo
    args: ["baz"]

Otherwise, you can specify the hooks as part of the Simulation custom resource object.

Running hooks #

All executables needed to run hooks must be present and on the path in the sk-ctrl pod (for pre-start and post-stop hooks) or in the sk-driver pod (for pre-run and post-run hooks). The standard Docker images built for SimKube include kubectl, curl, and jq for this purpose.