# Large-size infrastructure with Terraform

Source: <https://github.com/antonbabenko/terraform-best-practices/tree/master/examples/large-terraform>

This example contains code as an example of structuring Terraform configurations for a large-size infrastructure which uses:

* 2 AWS accounts
* 2 regions
* 2 separate environments (`prod` and `stage` which share nothing). Each environment lives in a separate AWS account and span resources between 2 regions
* Each environment uses a different version of the off-the-shelf infrastructure module (`alb`) sourced from [Terraform Registry](https://registry.terraform.io/)
* Each environment uses the same version of an internal module `modules/network` since it is sourced from a local directory.

{% hint style="info" %}
In a large project like described here the benefits of using Terragrunt become very visible. See [Code Structures examples with Terragrunt](https://www.terraform-best-practices.com/examples/terragrunt).
{% endhint %}

{% hint style="success" %}

* Perfect for projects where infrastructure is logically separated (separate AWS accounts)
* Good when there is no need to modify resources shared between AWS accounts (one environment = one AWS account = one state file)
* Good when there is no need for the orchestration of changes between the environments
* Good when infrastructure resources are different per environment on purpose and can't be generalized (eg, some resources are absent in one environment or in some regions)
  {% endhint %}

{% hint style="warning" %}
As the project grows, it will be harder to keep these environments up-to-date with each other. Consider using infrastructure modules (off-the-shelf or internal) for repeatable tasks.
{% endhint %}

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