Chaos Engineering Concepts in the Chaos Toolkit¶
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Chaos Engineering is a discipline that allows you to surface weaknesses, and eventually build confidence, in complex and often distributed systems.
The Chaos Toolkit aims to give you the simplest experience for writing and running your own Chaos Engineering experiments. The main concepts are all expressed in an experiment definition, of which the following is an example from the Chaos Toolkit Samples project:
{
"title": "System is resilient to provider's failures",
"description": "Can our consumer survive gracefully a provider's failure?",
"tags": [
"service",
"kubernetes",
"spring"
],
"steady-state-hypothesis": {
"title": "Services are all available and healthy",
"probes": [
{
"type": "probe",
"name": "all-services-are-healthy",
"tolerance": true,
"provider": {
"type": "python",
"module": "chaosk8s.probes",
"func": "all_microservices_healthy"
}
}
]
},
"method": [
{
"type": "action",
"name": "stop-provider-service",
"provider": {
"type": "python",
"module": "chaosk8s.actions",
"func": "kill_microservice",
"arguments": {
"name": "my-provider-service"
}
},
"pauses": {
"after": 10
}
},
{
"ref": "all-services-are-healthy"
},
{
"type": "probe",
"name": "consumer-service-must-still-respond",
"provider": {
"type": "http",
"url": "http://192.168.42.58:31018/invokeConsumedService"
}
}
],
"rollbacks": []
}
title: System is resilient to provider's failures
description: Can our consumer survive gracefully a provider's failure?
tags:
- service
- kubernetes
- spring
steady-state-hypothesis:
title: Services are all available and healthy
probes:
- type: probe
name: all-services-are-healthy
tolerance: true
provider:
type: python
module: chaosk8s.probes
func: all_microservices_healthy
method:
- type: action
name: stop-provider-service
provider:
type: python
module: chaosk8s.actions
func: kill_microservice
arguments:
name: my-provider-service
pauses:
after: 10
- ref: all-services-are-healthy
- type: probe
name: consumer-service-must-still-respond
provider:
type: http
url: http://192.168.42.58:31018/invokeConsumedService
rollbacks: []
The key concepts of the Chaos Toolkit are Experiments, Steady State Hypothesis and the experiment’s Method. The Method contains a combination of Probes and Actions.
Experiments¶
A Chaos Toolkit experiment is provided in a single file and is currently expressed in JSON.
Steady State Hypothesis¶
A Steady State Hypothesis describes “what normal looks like” for your system in order for the experiment to surface information about weaknesses when compared against the declared “normal” tolerances of what is measured.
The Chaos Toolkit uses the Steady State Hypothesis for two purposes. It is used as a check before an experiment is run that the target system is in a recognised normal state. It is also used as the template for comparison of the state of your system after the experiment has been run, forming the results provided by the experiment’s report.
Method¶
An experiment’s activities are contained within its Method block.
Probes¶
A probe is a way of observing a particular set of conditions in the system that is undergoing experimentation.
Actions¶
An action is a particular activity that needs to be enacted on the system under experimentation.
Rollbacks¶
An experiment may define a sequence of actions that revert what was undone during the experiment.
Controls¶
An experiment may declare a set of controls which have an impact over the execution of the experiment itself. Controls are operational elements rather than experimental.