# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   ec2_instance_nitro_encryption_in_transit_check
# 
# Description:
#   This control checks whether an EC2 instance has been configured to run using a Nitro instance type that supports encryption in-transit between instances.
# 
# Reports on:
#   AWS::EC2::Instance
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document does not contain any EC2 instance resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 instance resource
#       And: 'InstanceType' has not been provided
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 instance resource
#       And: 'InstanceType' been provided and set to an instance type other than a Nitro
#            instance type that supports encryption in-transit between instances
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 instance resource
#       And: 'InstanceType' been provided and set to a Nitro instance type that supports
#            encryption in-transit between instances
#      Then: PASS

#
# Constants
#
let INPUT_DOCUMENT = this
let EC2_INSTANCE_TYPE = "AWS::EC2::Instance"
let NITRO_ENCRYPTION_IN_TRANSIT_INSTANCE_TYPES = [
    /^c5a\..+?$/, /^c5ad\..+?$/, /^c5n\..+?$/, /^c6a\..+?$/, /^c6gn\..+?$/, /^c6i\..+?$/,
    /^c6id\..+?$/, /^c6in\..+?$/, /^c7a\..+?$/, /^c7g\..+?$/, /^c7gd\..+?$/, /^c7gn\..+?$/,
    /^c7i\..+?$/,
    /^d3\..+?$/, /^d3en\..+?$/, /^dl1\..+?$/, /^dl2q\..+?$/,
    /^g4ad\..+?$/, /^g4dn\..+?$/, /^g5\..+?$/,
    /^hpc6a\..+?$/, /^hpc6id\..+?$/, /^hpc7a\..+?$/, /^hpc7g\..+?$/,
    /^i3en\..+?$/, /^i4g\..+?$/, /^i4i\..+?$/, /^im4gn\..+?$/, /^inf1\..+?$/,
    /^inf2\..+?$/, /^is4gen\..+?$/,
    /^m5dn\..+?$/, /^m5n\..+?$/, /^m5zn\..+?$/, /^m6a\..+?$/, /^m6i\..+?$/, /^m6id\..+?$/,
    /^m6idn\..+?$/, /^m6in\..+?$/, /^m7a\..+?$/, /^m7g\..+?$/, /^m7gd\..+?$/,
    /^m7i-flex\..+?$/, /^m7i\..+?$/,
    /^p3dn\..+?$/, /^p4d\..+?$/, /^p4de\..+?$/, /^p5\..+?$/,
    /^r5dn\..+?$/, /^r5n\..+?$/, /^r6a\..+?$/, /^r6i\..+?$/, /^r6id\..+?$/, /^r6idn\..+?$/,
    /^r6in\..+?$/, /^r7a\..+?$/, /^r7g\..+?$/, /^r7gd\..+?$/, /^r7i\..+?$/, /^r7iz\..+?$/,
    /^trn1\..+?$/, /^trn1n\..+?$/,
    /^u-12tb1\..+?$/, /^u-18tb1\..+?$/, /^u-24tb1\..+?$/, /^u-3tb1\..+?$/, /^u-6tb1\..+?$/,
    /^u-9tb1\..+?$/,
    /^vt1\..+?$/,
    /^x2idn\..+?$/, /^x2iedn\..+?$/, /^x2iezn\..+?$/
]

#
# Assignments
#
let ec2_instances = Resources.*[ Type == %EC2_INSTANCE_TYPE ]

#
# Primary Rules
#
rule ec2_instance_nitro_encryption_in_transit_check when is_cfn_template(%INPUT_DOCUMENT)
                                                         %ec2_instances not empty {
    check(%ec2_instances.Properties)
        <<
        [CT.EC2.PR.19]: Require an EC2 instance to use an AWS Nitro instance type that supports encryption in-transit between instances when created using the AWS::EC2::Instance resource type
        [FIX]: Set 'InstanceType' to an EC2 instance type based on the AWS Nitro system that supports encryption in-transit between instances.
        >>
}

rule ec2_instance_nitro_encryption_in_transit_check when is_cfn_hook(%INPUT_DOCUMENT, %EC2_INSTANCE_TYPE) {
    check(%INPUT_DOCUMENT.%EC2_INSTANCE_TYPE.resourceProperties)
        <<
        [CT.EC2.PR.19]: Require an EC2 instance to use an AWS Nitro instance type that supports encryption in-transit between instances when created using the AWS::EC2::Instance resource type
        [FIX]: Set 'InstanceType' to an EC2 instance type based on the AWS Nitro system that supports encryption in-transit between instances.
        >>
}

#
# Parameterized Rules
#
rule check(ec2_instance) {
    %ec2_instance {
        # Scenario 2
        InstanceType exists
        # Scenarios 3 and 4
        InstanceType in %NITRO_ENCRYPTION_IN_TRANSIT_INSTANCE_TYPES
    }
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists  or
        Resources exists
    }
}

rule is_cfn_hook(doc, RESOURCE_TYPE) {
    %doc.%RESOURCE_TYPE.resourceProperties exists
}