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Randomized Simulations


Helmit supports simulation of [Kubernetes] and [Helm] applications using a custom simulation framework and command line tool. Simulations are collections of operations on a Kubernetes application that are randomized by the Helmit simulator. To run a simulation, write a Golang simulation suite and then run the suite using the helmit sim tool:

helmit sim ./cmd/sims

Writing Simulations

To run a simulation you must first define a simulation suite. Simulation suites are Golang structs containing a series of receivers that simulate operations on Kubernetes applications:

import ""

type AtomixSimSuite struct {

Helmit runs each suite within its own namespace, and each simulation consists of a set of simulator functions to run. Prior to running simulations, simulation suites typically need to set up resources within the Kubernetes namespace. Simulations can implement the following interfaces to manage the namespace: * SetupSimulation - Called on a single simulation pod prior to running a simulation * SetupSimulator - Called on each simulator pod prior to running a simulation

Typically, simulation suites should implement the SetupSimulation interface to install Helm charts:

func (s *AtomixSimSuite) SetupSimulation(c *simulation.Simulator) error {
    err := helm.Chart("atomix-controller").
        Set("scope", "Namespace").
    if err != nil {
        return err

    err = helm.Chart("atomix-database").
        Set("clusters", 3).
        Set("partitions", 10).
        Set("backend.replicas", 3).
        Set("backend.image", "atomix/raft-replica:latest").
    if err != nil {
        return err
    return nil

Simulator functions can be written with any name pattern:

import ""

var keys = input.RandomChoice(input.SetOf(input.RandomString(8), 1000))
var values = input.RandomBytes(128)

func (s *AtomixSimSuite) SimulateMapPut(c *simulation.Simulator) error {
    ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
    defer cancel()
    _, err := s.m.Put(ctx, keys.Next().String(), values.Next().Bytes())
    return err

Simulations must schedule their simulator functions by implementing the ScheduleSimulator interface:

func (s *AtomixSimSuite) ScheduleSimulator(sim *simulation.Simulator) {
    sim.Schedule("get", s.SimulateMapGet, 1*time.Second, 1)
    sim.Schedule("put", s.SimulateMapPut, 5*time.Second, 1)
    sim.Schedule("remove", s.SimulateMapRemove, 30*time.Second, 1)

When scheduling simulators, the simulation specifies a default rate at which the simulators are executed. Note that simulator rates can be overridden from the simulator command line

Registering Simulation Suites

In order to run simulations, a main must be provided that registers and names simulation suites.

import ""

func init() {
    registry.RegisterSimulationSuite("atomix", &sims.AtomixSimulationSuite{})

Once the simulations have been registered, the main should call simulation.Main() to run the simulations:

import (
    simulations ""

func main() {
    registry.RegisterSimulationSuite("atomix", &sims.AtomixSimulationSuite{})

Running Simulations

Simulations are run using the helmit sim command. To run a simulation, run helmit sim with the path to the command in which simulations are registered:

helmit sim ./cmd/simulations

By default, the helmit sim command will run every simulation registered in the provided main. To run a specific simulation, use the --simulation flag:

helmit sim ./cmd/simulations --suite atomix

Simulations can either be run for a configurable duration of time:

helmit sim ./cmd/simulations --duration 10m

By default, simulations are run on a single client pod. Simulations can be scaled across many client pods by setting the --simulators flag:

helmit sim ./cmd/simulations --duration 10m --simulators 10

As with all Helmit commands, the helmit sim command supports contexts and Helm values and value files:

helmit sim ./cmd/simulations -c . -f kafka=kafka-values.yaml --set kafka.replicas=2 --duration 10m