I had some spare time last month and decided it was time to take a closer look at Azure Chaos Studio, which is a managed service that allows you to orchestrate fault injection on your Azure resources, or inside of virtual machines, in a controlled manner. It helps you to perform chaos engineering on the Azure platform. Before my encounter with Azure Chaos Studio, I had also tinkered with Chaos Toolkit. It is open-source software that can be used to perform chaos engineering experiments.
A friend of mine asked me whether I could combine PowerShell, Pester 5 (a test and mock framework for PowerShell) and Azure Chaos Studio, in order to perform chaos experiments in a similar fashing to how Chaos Toolkit does it. If I wanted to tackle this I figured I'd have to go back and see what a Chaos Toolkit experiment consists of. When you run a Chaos Toolkit experiment, the following actions take place:
- A first check (or pass, as I refer to it) of the steady-state hypothesis.
- Defines what the working state of our app should be.
- For example: does this call to our web page return a status code 200?
- A method block.
- Changes the conditions of our system.
- For example: block incoming traffic on the firewall.
- A second pass of the same steady-state hypothesis.
- This is to validate that everything is still working as intended.
- A rollback block
- Does what it needs to, to roll back the changes introduced by the method block.
The method, second steady-state hypothesis pass and rollback blocks can only be executed when the first steady-state hypothesis pass was completed succesfully.
After reading through all that, wasn't quite certain whether I could build something similar with PowerShell and Pester 5... But I think I've managed to come up with something that can work, after all.
Feel free to read the full blog post!
You will need to run the Pester (chaos experiment) test against! The following template creates a simple web server, which will be sitting in a web subnet on the virtual network, a network security group will be associated with the web subnet. Through the use of a chaos experiment, we will inject a faulty inbound rule, in the network security group, for just a few minutes. This should cause the website to become unreachable!
