The depends_on Meta-Argument

Use the depends_on meta-argument to handle hidden resource or module dependencies that Terraform cannot automatically infer. You only need to explicitly specify a dependency when a resource or module relies on another resource's behavior but does not access any of that resource's data in its arguments.

Example

A good example of this is in an Application Security configuration exported with the cli-terraform (opens in a new tab).

The security module (we'll soon talk about modules) acts as a container for all security-related configurations. When you activate a security configuration, you want to ensure ALL security controls are properly configured first. In other words nothing in activate-security will proceed until the entire security module is complete

module "security" {
    source      = "./modules/security"
    hostnames   = var.hostnames
    name        = var.name
    description = var.description
    contract_id = var.contract_id
    group_name  = var.group_name
}
 
module "activate-security" {
    source              = "./modules/activate-security"
    name                = var.name
    config_id           = module.security.config_id
    network             = var.network
    notification_emails = var.emails
    note                = var.activation_note
    depends_on          = [ 
        module.security 
    ]
}

Exercise