driftctl/docs/middlewares.md

Middlewares

The main goal of middlewares is to reconciliate IaC and remote resources. For this we filter default resources, mutate, or remove fields in resources or even create and delete new resources.

type AwsDefaultRoute struct{}

func NewAwsDefaultRoute() AwsDefaultRoute {
	return AwsDefaultRoute{}
}

func (m AwsDefaultRoute) Execute(remoteResources, resourcesFromState *[]*resource.Resource) error {

	newRemoteResources := make([]*resource.Resource, 0)

	// ...

	*remoteResources = newRemoteResources

  return nil
}

In the above example, we define a middleware called AwsDefaultRoute that will modify remote resources. Middleware can access two arrays of type *[]*resource.Resource: IaC resources first and then remote resources. The goal is to rework these slices to remove false positive drifts. Notice both remoteResources and resourcesFromState variables are pointers, which mean middlewares can perform mutations on resources before the comparison is made.

Different kind of middlewares

1. Help driftctl match IaC resources and remote resources.
2. Filter noises from provider default resources
3. Resource transformation
4. Specific edge cases

Examples

1. aws_route_table_expander explode inline route in dedicated resources
2. aws_default_route ignore route created by default when creating a table if they are not managed in IaC
3. aws_iam_user_policy_attachment and aws_iam_role_policy_attachment transformed to aws_iam_policy_attachment
4. route53_records_id_reconcilier that rework ID's to match Terraform ones