Update SG rule input variable defaults to null

[alexbasista]

Description

Be consistent with evaluating AWS security group rules creation based on null variable value rather than the length of a list. The following inputs defaulted to an empty list ([]) which can cause issues when transitioning from a populated list to an empty list (default value), given how the count logic currently exists within the resources.

• cidr_allow_ingress_ec2_ssh
• cidr_allow_ingress_tfe_metrics_http
• cidr_allow_ingress_tfe_metrics_https
• cidr_allow_egress_ec2_dns

When changing the value of an input from a list with one or more items in it to an empty list, Terraform wants to replace the resources, but they shouldn't really be recreated if the list is empty. Terraform will run for at least 10 minutes on the create operation until it reaches a timeout.

Error: waiting for Security Group (sg-0c30e23a66c96e769) Rule (sgrule-1073862818) create: couldn't find resource

Related issue

N/A

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)
• This change requires a documentation update

How has this been tested?

Transition from running terraform apply while the variables are populated with CIDR ranges in a list, to commenting them out and running another terraform apply which causes them to take on the default value of null - with no issue. Going back and forth between the two configurations without Terraform hanging/timing out.

Checklist

• [x ] My code follows the style guidelines of this project
• [x ] I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Additional notes

N/A

[abuxton]

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[jkellner-hashi]

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