Loosely coupled Terraform framework making complex infrastructure understandable and scalable.
CatStack is a Terraform/OpenTofu framework that originated within TechNative. The framework solves several crucial problems that Cloud Engineers face when performing migrations and helps them set up completely new projects much faster. CatStack draws inspiration from frameworks in the software development world without trying to resemble them.
The main principles of CatStack are:
- "Don't repeat yourself" (DRY)
- Domain-separated organization of infrastructure
CatStack is designed to be used without having to install additional software except for Terraform/OpenTofu itself.
No, we're not making it prettier than it is. CatStack is simply a well-considered collection of conventions, best practices, and a directory structure that bundles multiple Terraform projects together. All of this combined delivers a comprehensible and scalable IaC project that increases productivity for any cloud team, whether small or large.
These are the advantages of building a terraform project with CatStack.
By dividing infrastructure into logical domains, multiple engineers can
collaborate on a larger project. CatStack has best practices, but in principle,
a team is free to determine its own domains. A domain has its own
terraform state, so as long as engineers don't work on a domain simultaneously,
they can use terraform apply whenever they want.
CatStack helps engineers write efficient source code that is reusable. First, CatStack implements multi-environments in a clear and scalable way. An environment can be deployed in multiple ways but the most obvious application is to separate production and non-production cloud accounts from each other. Heavier resources can be configured for the production account. The source code that defines the resources is shared across all environments.
Through Terraform's data blocks, resources from one domain can read necessary information from the state of another domain.
CatStack offers the possibility to place project-specific terraform code that appears in multiple domains in a shared library.
This is a programming pattern that CatStack encourages, but that every good Terraform programmer naturally knows and applies. As soon as you define multiple nearly identical resources within a domain, you create a module. You do this within the domain. You can compare this to creating a function in a generic programming language.
Within a domain, you can of course make use of Terraform's powerful module system. Use any of the thousands of modules from the Terraform Registry, or reference previously written modules in a git repo. Don't limit yourself because Terraform modules are the building blocks of the Cloud.
CatStack is incredibly flexible. Any application can be captured within the CatStack framework. And this while maintaining the ability to make as much use as possible of existing building blocks. This combination of qualities makes CatStack ideal for teams that execute many projects. Each project is tailor-made, and at the same time, each project contributes to the projects that are yet to come.
Just like Terraform is suitable for AWS, Azure, or any other provider... CatStack is just as versatile. It's even possible within a CatStack project to have multiple providers working together. As a fun experiment, we built a several projects in MineCraft with CatStack and the Terraform MineCraft provider.
As stated earlier, CatStack is a framework that can be used with Terraform as its only dependency. However, because CatStack is based on smart conventions, it offers excellent opportunities to make tasks even easier. TechNative has created quite a few scripts and small programs for AWS that make our engineers even more productive.
At TechNative, we work with the rule: feel free to use all those handy scripts that allow you to work faster. But not before you understand how Terraform works and how CatStack is structured.
Here's a list of CatStack tooling we use withing TechNative:
- RACE - Terraform Tools for TechNative CatStack
- Bootstrap-AWS-CatStack - Bootstrap-AWS-CatStack Script
What does the name CatStack mean?
CatStack doesn't mean that much. A cat is a nice animal. You can read it as: Cloud AWS Terraform Stack.
Does CatStack also work with OpenTofu instead of Terraform?
CatStack is 100% compatible with OpenTofu.
infra_environments: infra_environments short for infrastructure environments are the AWS accounts where resources will be created and hosted.
xxx.tfvars.json: This file hosts Terraform variables that are shared between the domains and stacks.
xxx.tfbackend: This file hosts the details of the Terraform backend configuration for that specific infrastructure environment.
Domain: Domains are directories which contains the IaC code of the resources deployed. Domains have numbers infront of them which indicates in which order of the Stack they are applied. For example, Domains starting with 001 means that the resources in those domains are the first that should be deployed in an environment.
Stack: The Stack directory contains the directory of all domains. Think of a Stack as a kitchen drawer and the contents in that drawer are known as domains.
Module: A module is a group of resources that together provide a certain value for a domain or stack.
A CatStack is a composition of domains. A domain is an autonomous Terraform component with its own seperated Terraform state. You can have low level domains and higher level domains, E.g. the KMS domain is a low level domain as it has many dependants, while an EC2 instance domain is high level domain. Like any other vanilla Terraform project, a CatStack domain can use terraform modules.
A CatStack domain is not distributed as an installable module, but its more like glue code for one or more resources to define an infrastruture component in a larger system or solution.