S3-shield: Terraform and docs updates

[mariusmagureanu]

Synopis

This PR aims to introduce some minimal Terraform best practices, along with a newer TF and AWS provider version.

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Implementation

• prefer lower case variables, upper case ones are usually reserved for environment variables
• prefer underscore instead of dashes in resource or data-lookup names
• run terraform fmt against all terraform files
• prefer variables instead of hardcoded values in data-lookups
• remove default values for mandatory variables (e.g. key_name)
• extend the README with Terraform requirements/providers/inputs/outputs
• added a pre-commit goodie to format tf files and update the README file accordingly
• moved from t2.micro to t3.micro as default instance type

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Notes

The tables in the README file have automatically been generated with:

• pre-commit
• terraform-docs

by running the folllowing in the terraform-aws folder:

$ pre-commit run --show-diff-on-failure --all-files terraform_docs

---

Potential trouble

This section is relevant only if you already have provisioned infrastructure. Otherwise, if starting from scratch - skip the following lines.

The tf-ve6 resource has been renamed to tf_ve6.

If you'll plan this code against already provisioned infra, then Terraform will attempt to create a new aws_instance resource.

You most likely don't want that - as you already have the instance you need. However, this situation can easily be handled using the Terraform moved block.

Example:

moved {
    from = aws_instance.tf-ve6
    to = aws_instance.tf_ve6
}