AWS security groups failing to provision

[cynicXer]

For AWS http-c2 and dns-c2 modules, terraform fails to correctly interpolate the public IP address when creating the SSH ingress rule in security-group.tf. The security group resource creation fails silently unless ERROR logging is enabled, which generates the following:

2019/02/07 16:43:06 [ERROR] root.dns_c2: eval: *terraform.EvalValidateResource, err: Warnings: []. Errors: ["ingress.0.cidr_blocks.0" must contain a valid CIDR, got error parsing: invalid CIDR address: /32]

I verified the data/scripts/get_public_ip.sh script works when run locally. "terraform plan" works when I change the line in security-group.tf from:

cidr_blocks = ["${data.external.get_public_ip.result["ip"]}/32"]
to:
cidr_blocks = ["0.0.0.0/0"]

Thank you.