They somewhat compliment each other, they are not really alternatives to each other. Usually Ansible is used for declaring the desired state of the individual

They somewhat compliment each other, they are not really alternatives to each other. Usually Ansible is used for declaring the desired state of the individual servers for example you may use it to manage installed packages and configuration files on the servers. Whereas with Terraform you declare the desired state of cloud resources for example you may ask Terraform to give you 5 EC2 instances, 1 RDS instance for DB and 1 S3 bucket for storage. There's some overlap between them but what I've said is largely accurate.