There could be scenarios where you want to import the already existing resources from cloud providers into terraform.
Terraform has an import modude which does this job and using the module is a tedious process
https://www.terraform.io/docs/cli/import/index.html
There is tool called Terraformer which does the job of reverese terraforming
https://github.com/GoogleCloudPlatform/terraformer
Google cloud
https://gist.github.com/kiranchavala/54a930c8da148cc2b637c053dc1ba8ba
AWS
https://gist.github.com/kiranchavala/c2a01a7a43ea15cb8921a710d6cf22ea
Azure
https://gist.github.com/kiranchavala/18a1c555c198eb0944cbad3791602dc7
Openstack
https://gist.github.com/kiranchavala/c63243b0b76adcdafc7d06d87a304370
Cloudstack
https://gist.github.com/kiranchavala/c1b81f1d629b0567e08e219891d4ed48