Structure.md

Repository Structure

The Repository structure is as follows:

.
+-- app
|   +-- components
|       +-- ...
|   +-- modules
|       +-- ...
|   +-- stacks
|       +-- global
|           +-- ...
|       +-- uk-south
|           +-- ...
|       +-- uk-west
|           +-- ...
+-- config
|   +-- variables
|       +-- stacks
|           +-- ...
|       +-- dev.hcl
|       +-- global.hcl
|       +-- prod.hcl
|       +-- test.hcl
|   +-- backend.tf
|   +-- provider.tf
|   +-- terragrunt.hcl
+-- pipelines
|   +-- infra-cd.yml
|   +-- infra-cd.yml
+-- .gitignore
+-- .pre-commit-config.yaml
+-- .tflint.hcl

• app: contains the Terraform modules. These are broken down into 3 types.

-	-
Modules	Small re-usable modules with a collection of resources that are used together often. These are referenced by stacks.
Components	Larger collection of resources and sub-modules that will be deployed across multiple stacks. These are referenced by stacks.
Stacks	The main stack of resources e.g. the Appeals service in the UK West region.

• config: contains the configuration for the project with things like variables for each environment.

• The project uses Terragrunt to deploy and manage the Terraform modules. This works via the parent and child terragrunt.hcl files. The parent file is located within the config folder, and contains the re-usable configuration across all stacks such as remote backend etc. The child terragrunt.hcl file is located in each stack folder. For example, when deploying the UK West Appeals Service stack, the child terragrunt.hcl file is read from app/stacks/uk-west/appeals-service/terragrunt.hcl and the parent is read from config/terragrunt.hcl.

• The variables are divided up into *.hcl files in the variables folder. The global.hcl file contains global variables, and there are also variables for each environment e.g. dev.hcl. There are also variables specific to each stack in the config/varirables/stacks/<stack_name>/<environment>.hcl files. These files are loaded in the parent terragrunt.hcl file.

• pipelines: contains Azure pipelines specified as YAML templates.

• Various config files are located at the project root e.g. .tflint.hcl.

Entry point

Each stack in the stacks directory has an app-service.tf file. This can be seen as the entry point of that stack. Other resources instantiated alongside it are typically referenced by the app-service.tf file.

infrastructure-modules

The infrastructure-modules repository contains some custom modules imported by this repository.

For example, the app/components/back-office-app-services/app-service.tf file instantiates node-app-service, which is a custom module that handles most of the setup for a Linux-based web application.

Regions

The primary region for the applications is UK West, with a secondary region of UK South for failover. This is why the stacks folder is organised as it is. Global infrastructure such as Front Door is located in the global folder.