# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   elasticsearch_data_node_fault_tolerance_check
# 
# Description:
#   This control checks whether ElasticSearch domains are configured with at least three data nodes and zone awareness enabled.
# 
# Reports on:
#   AWS::Elasticsearch::Domain
# 
# 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 Elasticsearch domain resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'ElasticsearchClusterConfig' 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 Elasticsearch domain resource
#       And: 'ElasticsearchClusterConfig' has been provided
#       And: 'ZoneAwarenessEnabled' in 'ElasticsearchClusterConfig' has not been provided
#             or provided and set to a value other than bool(true)
#       And: 'InstanceCount' in 'ElasticsearchClusterConfig' has not been provided or
#             provided and set to an integer value less than three (< 3)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'ElasticsearchClusterConfig' has been provided
#       And: 'ZoneAwarenessEnabled' in 'ElasticsearchClusterConfig' has been provided
#             and set to bool(true)
#       And: 'InstanceCount' in 'ElasticsearchClusterConfig' has not been provided or
#             provided and set to an integer value less than three (< 3)
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'ElasticsearchClusterConfig' has been provided
#       And: 'ZoneAwarenessEnabled' in 'ElasticsearchClusterConfig' has not been provided
#             or provided and set to a value other than bool(true)
#       And: 'InstanceCount' in 'ElasticsearchClusterConfig' has been provided and set to
#             an integer value greater than or equal to three (>= 3)
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Elasticsearch domain resource
#       And: 'ElasticsearchClusterConfig' has been provided
#       And: 'ZoneAwarenessEnabled' in 'ElasticsearchClusterConfig' has been provided
#             and set to bool(true)
#       And: 'InstanceCount' in 'ElasticsearchClusterConfig' has been provided and set to
#             an integer value greater than or equal to three (>= 3)
#      Then: PASS

#
# Constants
#
let ELASTICSEARCH_DOMAIN_TYPE = "AWS::Elasticsearch::Domain"
let INPUT_DOCUMENT = this

#
# Assignments
#
let elasticsearch_domains = Resources.*[ Type == %ELASTICSEARCH_DOMAIN_TYPE ]

#
# Primary Rules
#
rule elasticsearch_data_node_fault_tolerance_check when is_cfn_template(%INPUT_DOCUMENT)
                                                        %elasticsearch_domains not empty {
    check(%elasticsearch_domains.Properties)
        <<
        [CT.OPENSEARCH.PR.6]: Require an Elasticsearch domain to have zone awareness and at least three data nodes
        [FIX]: Within 'ElasticsearchClusterConfig', set 'ZoneAwarenessEnabled' to 'true', and set 'InstanceCount' to an integer value greater than or equal to three.
        >>
}

rule elasticsearch_data_node_fault_tolerance_check when is_cfn_hook(%INPUT_DOCUMENT, %ELASTICSEARCH_DOMAIN_TYPE) {
    check(%INPUT_DOCUMENT.%ELASTICSEARCH_DOMAIN_TYPE.resourceProperties)
        <<
        [CT.OPENSEARCH.PR.6]: Require an Elasticsearch domain to have zone awareness and at least three data nodes
        [FIX]: Within 'ElasticsearchClusterConfig', set 'ZoneAwarenessEnabled' to 'true', and set 'InstanceCount' to an integer value greater than or equal to three.
        >>
}

#
# Parameterized Rules
#
rule check(elasticsearch_domain) {
    %elasticsearch_domain {
        # Scenario 2
        ElasticsearchClusterConfig exists
        ElasticsearchClusterConfig is_struct

        ElasticsearchClusterConfig {
            # Scenario 3, 4, 5 and 6
            ZoneAwarenessEnabled exists
            ZoneAwarenessEnabled == true

            InstanceCount exists
            InstanceCount >= 3
        }
    }
}

#
# 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
}