What is the role of 'depends_on' in Terraform modules?

The role of 'depends_on' in Terraform modules is to declare resource dependencies. This functionality is crucial in situations where the order of resource creation is essential. By explicitly defining dependencies using 'depends_on', you ensure that Terraform executes your resources in the specified sequence, which is necessary for ensuring the correct functionality and integrity of your infrastructure.

For example, if you have a resource that relies on another resource to be fully created before it can be initiated, using 'depends_on' allows you to enforce this order. Without this specification, Terraform may not be aware of the dependency, potentially leading to errors where resources attempt to interact prematurely, such as trying to use outputs from a resource that hasn't yet been created.

Understanding how resource dependencies work is a key part of managing infrastructure in Terraform, allowing for better organization, performance, and reliability in deployments.