Error: Reference to undeclared resource

 terraform plan
╷
│ Error: Reference to undeclared resource
│
│   on main.tf line 9, in resource "aws_instance" "example":
│    9:   ami               = data.aws_ami.windows.id
│
│ A data resource "aws_ami" "windows" has not been declared in the root module.

╷
│ Error: Reference to undeclared resource
│
│   on main.tf line 14, in resource "aws_db_instance" "my_mariadb_instance":
│   14:   db_subnet_group_name = vpc.subnet-0526dd2XXXXXX
│
│ A managed resource "vpc" "subnet-0526dd2e6fce5492b" has not been declared in the root module.
╵

╷
│ Error: Reference to undeclared resource
│
│   on main.tf line 16, in resource "aws_db_instance" "my_mariadb_instance":
│   16:   db_subnet_group_name =  "${aws_db_subnet_group.default.id}"
│
│ A managed resource "aws_db_subnet_group" "default" has not been declared in the root module.
╵

Related

• Terraform plan execution with errors: Error: Reference to undeclared module

See also

• terraform plan: [ -refresh-only | -lock=false | -target | -var-file | will be created | --help], Terraform plan errors, Terraform plan examples, Terraform plan execution errors, (known after apply)