Is it possible to append a parent module argument?

For example, I have a parent module that creates aws_db_instance resource,
with the tags argument:

tags = {
Name = “test”
Service = “service1”
Environment = “development”

Is there any way that I can append/modify this argument from a child module?

Use case is I want to add more tags to the RDS instance without modifying the parent module.

Hi @derianpt,

Data flow in Terraform is always explicit, so there is no way for a child module to implicitly alter the content of a parent module.

The closest you can get here is to make your child module export a map of additonal tags and then explicitly merge that with the tags in your RDS instance block, so that the value is clearly defined in the configuration:

  tags = merge(module.example.additional_tags, {
    Name        = "test"
    Service     = "service1"
    Environment = "development"
1 Like

Thanks Martin. Even though this requires a one time update to the parent module, it fulfils the use case :grinning: