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https://github.com/wearetechnative/catstack

Loosely coupled Terraform framework making complex infrastructure understandable and scalable.
https://github.com/wearetechnative/catstack

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Loosely coupled Terraform framework making complex infrastructure understandable and scalable.

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README 

          
# CatStack



Loosely coupled Terraform framework making complex infrastructure

understandable and scalable.






## What is CatStack?



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.



## Is CatStack magic?



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.



## The advantages of CatStack



These are the advantages of building a terraform project with CatStack.



### Collaboration in a team environment



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.



### DRY and multi-environments



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.



### DRY and data blocks



Through Terraform's data blocks, resources from one domain can read necessary

information from the state of another domain.



### DRY and shared code libraries



CatStack offers the possibility to place project-specific terraform code that

appears in multiple domains in a shared library.



### DRY and Domain modules



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.



### DRY and Terraform remote modules



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.



### Flexible



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.



### Cloud Agnostic



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.



### Optional tooling



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](https://github.com/wearetechnative/race) - Terraform Tools for TechNative CatStack 

- [Bootstrap-AWS-CatStack](https://github.com/wearetechnative/bootstrap-aws-catstack) - Bootstrap-AWS-CatStack Script



## FAQ



> 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.



## Definition of Terms



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.



## Documentation



For more detailed documentation, see the [docs](./docs/) directory:



- [Architecture](./docs/architecture.md) - Detailed CatStack architecture and structure



## Domains



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.