# Amazon Simple Queue Service (Amazon SQS) controls
<a name="sqs-rules"></a>

**Topics**
+ [[CT.SQS.PR.1] Require any Amazon SQS queue to have a dead-letter queue configured](#ct-sqs-pr-1-description)
+ [[CT.SQS.PR.2] Require any Amazon SQS queue to have encryption at rest configured](#ct-sqs-pr-2-description)

## [CT.SQS.PR.1] Require any Amazon SQS queue to have a dead-letter queue configured
<a name="ct-sqs-pr-1-description"></a>

This control checks whether an Amazon SQS queue is configured with a dead-letter queue.
+ **Control objective: **Improve resiliency
+ **Implementation: **CloudFormation Guard Rule
+ **Control behavior: **Proactive
+ **Resource types: **`AWS::SQS::Queue`
+ **CloudFormation guard rule: ** [CT.SQS.PR.1 rule specification](#ct-sqs-pr-1-rule) 

**Details and examples**
+ For details about the PASS, FAIL, and SKIP behaviors associated with this control, see the: [CT.SQS.PR.1 rule specification](#ct-sqs-pr-1-rule) 
+ For examples of PASS and FAIL CloudFormation Templates related to this control, see: [CT.SQS.PR.1 example templates](#ct-sqs-pr-1-templates) 

**Explanation**

The main task of a dead-letter queue is to handle the lifecycle of unconsumed messages. A dead-letter queue lets you set aside and isolate messages that can`t be processed correctly, so you can determine why their processing didn`t succeed.

**Usage considerations**  
This control applies only to Amazon SQS queues that are not configured as a dead-letter queue with a `RedriveAllowPolicy` property.

### Remediation for rule failure
<a name="ct-sqs-pr-1-remediation"></a>

Create a `RedrivePolicy` with a `deadLetterTargetArn` value that`s set to the ARN of an Amazon SQS dead-letter queue. For Amazon SQS dead-letter queues, instead provide a redrive configuration in the `RedriveAllowPolicy' property.

The examples that follow show how to implement this remediation.

#### Amazon SQS Queue - Example
<a name="ct-sqs-pr-1-remediation-1"></a>

Amazon SQS queue configured to send messages to a dead-letter queue, if the messages can't be processed (consumed) successfully. The example is shown in JSON and in YAML.

**JSON example**

```
{
    "SQSQueue": {
        "Type": "AWS::SQS::Queue",
        "Properties": {
            "RedrivePolicy": {
                "deadLetterTargetArn": {
                    "Fn::GetAtt": [
                        "DLQQueue",
                        "Arn"
                    ]
                },
                "maxReceiveCount": 3
            }
        }
    }
}
```

**YAML example**

```
SQSQueue:
  Type: AWS::SQS::Queue
  Properties:
    RedrivePolicy:
      deadLetterTargetArn: !GetAtt 'DLQQueue.Arn'
      maxReceiveCount: 3
```

### CT.SQS.PR.1 rule specification
<a name="ct-sqs-pr-1-rule"></a>

```
# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#    sqs_dlq_check
# 
# Description:
#   This control checks whether an Amazon SQS queue is configured with a dead-letter queue.
# 
# Reports on:
#    AWS::SQS::Queue
# 
# Evaluates:
#    CloudFormation, CloudFormation hook
# 
# Rule Parameters:
#     None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document does not contain any SQS queue resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'RedriveAllowPolicy' has been provided on the SQS queue
#       And: 'RedriveAllowPolicy.redrivePermission' is set to 'allowAll' or 'byQueue'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'RedriveAllowPolicy' has not been provided on the SQS queue or 'RedriveAllowPolicy.redrivePermission'
#            has been provided and is set to a value other than 'allowAll' or 'byQueue'
#       And: 'RedrivePolicy' has not been provided
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'RedriveAllowPolicy' has not been provided on the SQS queue or 'RedriveAllowPolicy.redrivePermission'
#            has been provided and is set to a value other than 'allowAll' or 'byQueue'
#       And: 'RedrivePolicy' has been provided
#       And: 'RedrivePolicy.deadLetterTargetArn' has not been provided or has been provided as an empty string or
#            invalid local reference to an SQS queue
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'RedriveAllowPolicy' has not been provided on the SQS queue or 'RedriveAllowPolicy.redrivePermission' has
#            been provided and is set to a value other than 'allowAll' or 'byQueue'
#       And: 'RedrivePolicy' has been provided
#       And: 'RedrivePolicy.deadLetterTargetArn' has been provided as a non-empty string or valid local reference to
#             an SQS queue
#      Then: PASS

#
# Constants
#
let SQS_QUEUE_TYPE = "AWS::SQS::Queue"
let INPUT_DOCUMENT = this
let DLQ_REDRIVE_PERMISSION = ["allowAll", "byQueue"]

#
# Assignments
#
let sqs_queues = Resources.*[ Type == %SQS_QUEUE_TYPE ]

#
# Primary Rules
#
rule sqs_dlq_check when is_cfn_template(%INPUT_DOCUMENT)
                        %sqs_queues not empty {
    check(%sqs_queues.Properties)
        <<
        [CT.SQS.PR.1]: Require any Amazon SQS queue to have a dead-letter queue configured
            [FIX]: Create a 'RedrivePolicy' with a 'deadLetterTargetArn' value that's set to the ARN of an Amazon SQS dead-letter queue. For Amazon SQS dead-letter queues, instead provide a redrive configuration in the 'RedriveAllowPolicy' property.
        >>
}

rule sqs_dlq_check when is_cfn_hook(%INPUT_DOCUMENT, %SQS_QUEUE_TYPE) {
    check(%INPUT_DOCUMENT.%SQS_QUEUE_TYPE.resourceProperties)
        <<
        [CT.SQS.PR.1]: Require any Amazon SQS queue to have a dead-letter queue configured
            [FIX]: Create a 'RedrivePolicy' with a 'deadLetterTargetArn' value that's set to the ARN of an Amazon SQS dead-letter queue. For Amazon SQS dead-letter queues, instead provide a redrive configuration in the 'RedriveAllowPolicy' property.
        >>
}

#
# Parameterized Rules
#
rule check(sqs_queues) {
    %sqs_queues [
        # Scenario 2
        RedriveAllowPolicy not exists or
        filter_is_not_dlq(this)
    ] {
        # Scenario 3
        RedrivePolicy exists
        RedrivePolicy is_struct

        # Scenario 4
        RedrivePolicy {
            deadLetterTargetArn exists

            check_is_string_and_not_empty(deadLetterTargetArn) or
            check_local_references(%INPUT_DOCUMENT, deadLetterTargetArn, %SQS_QUEUE_TYPE)
        }
    }
}

rule filter_is_not_dlq(sqs_queue) {
    RedriveAllowPolicy exists
    RedriveAllowPolicy is_struct

    RedriveAllowPolicy {
        redrivePermission exists
        redrivePermission not in %DLQ_REDRIVE_PERMISSION
    }
}

#
# 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
}

rule check_is_string_and_not_empty(value) {
    %value {
        this is_string
        this != /\A\s*\z/
    }
}

rule check_local_references(doc, reference_properties, referenced_resource_type) {
    %reference_properties {
        "Fn::GetAtt" {
            query_for_resource(%doc, this[0], %referenced_resource_type)
                <<Local Stack reference was invalid>>
        } or Ref {
            query_for_resource(%doc, this, %referenced_resource_type)
                <<Local Stack reference was invalid>>
        }
    }
}

rule query_for_resource(doc, resource_key, referenced_resource_type) {
    let referenced_resource = %doc.Resources[ keys == %resource_key ]
    %referenced_resource not empty
    %referenced_resource {
        Type == %referenced_resource_type
    }
}
```

### CT.SQS.PR.1 example templates
<a name="ct-sqs-pr-1-templates"></a>

You can view examples of the PASS and FAIL test artifacts for the AWS Control Tower proactive controls.

PASS Example - Use this template to verify a compliant resource creation.

```
Resources:
  SQSQueue:
    Type: AWS::SQS::Queue
    Properties:
      RedrivePolicy:
        deadLetterTargetArn:
          Fn::GetAtt: [DLQQueue, Arn]
        maxReceiveCount: 3
  DLQQueue:
    Type: AWS::SQS::Queue
    Properties:
      RedriveAllowPolicy:
        redrivePermission: allowAll
```

FAIL Example - Use this template to verify that the control prevents non-compliant resource creation.

```
Resources:
  SQSQueue:
    Type: AWS::SQS::Queue
    Properties: {}
```

## [CT.SQS.PR.2] Require any Amazon SQS queue to have encryption at rest configured
<a name="ct-sqs-pr-2-description"></a>

This control checks whether an Amazon SQS queue is encrypted at rest.
+ **Control objective: **Encrypt data at rest
+ **Implementation: **CloudFormation Guard Rule
+ **Control behavior: **Proactive
+ **Resource types: **`AWS::SQS::Queue`
+ **CloudFormation guard rule: ** [CT.SQS.PR.2 rule specification](#ct-sqs-pr-2-rule) 

**Details and examples**
+ For details about the PASS, FAIL, and SKIP behaviors associated with this control, see the: [CT.SQS.PR.2 rule specification](#ct-sqs-pr-2-rule) 
+ For examples of PASS and FAIL CloudFormation Templates related to this control, see: [CT.SQS.PR.2 example templates](#ct-sqs-pr-2-templates) 

**Explanation**

Server-side encryption (SSE) allows you to transmit sensitive data in encrypted queues. To protect the content of messages in queues, SSE uses KMS keys.

### Remediation for rule failure
<a name="ct-sqs-pr-2-remediation"></a>

Set `SqsManagedSseEnabled` to `true` or set an AWS KMS key identifier in the `KmsMasterKeyId` property.

The examples that follow show how to implement this remediation.

#### Amazon SQS Queue - Example One
<a name="ct-sqs-pr-2-remediation-1"></a>

Amazon SQS queue configured to encrypt data at rest with server-side encryption enabled, by means of SQS managed encryption keys (SSE-SQS). The example is shown in JSON and in YAML.

**JSON example**

```
{
    "SQSQueue": {
        "Type": "AWS::SQS::Queue",
        "Properties": {
            "SqsManagedSseEnabled": true
        }
    }
}
```

**YAML example**

```
SQSQueue:
  Type: AWS::SQS::Queue
  Properties:
    SqsManagedSseEnabled: true
```

The examples that follow show how to implement this remediation.

#### Amazon SQS Queue - Example Two
<a name="ct-sqs-pr-2-remediation-2"></a>

Amazon SQS queue configured to encrypt data at rest with server-side encryption enabled, by means of AWS KMS (SSE-KMS). The example is shown in JSON and in YAML.

**JSON example**

```
{
    "SQSQueue": {
        "Type": "AWS::SQS::Queue",
        "Properties": {
            "KmsMasterKeyId": {
                "Ref": "KMSKey"
            }
        }
    }
}
```

**YAML example**

```
SQSQueue:
  Type: AWS::SQS::Queue
  Properties:
    KmsMasterKeyId: !Ref 'KMSKey'
```

### CT.SQS.PR.2 rule specification
<a name="ct-sqs-pr-2-rule"></a>

```
# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#    sqs_queue_encrypted_check
# 
# Description:
#   This control checks whether an Amazon SQS queue is encrypted at rest.
# 
# Reports on:
#    AWS::SQS::Queue
# 
# Evaluates:
#    CloudFormation, CloudFormation hook
# 
# Rule Parameters:
#     None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document does not contain any SQS queue resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' or 'SqsManagedSseEnabled' have not been provided on the SQS queue resource
#      Then: FAIL
#   Scenario: 3
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' has not been provided
#       And: 'SqsManagedSseEnabled' has been provided and set to bool(false)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' has been provided as an empty string or invalid local reference to a KMS key or alias
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'SqsManagedSseEnabled' is not provided or set to bool(false)
#       And: 'KmsMasterKeyId' is provided as a non-empty string or local reference to a KMS key
#      Then: PASS
#   Scenario: 6
#     Given: The input document is an CloudFormation or CloudFormation hook document
#       And: The input document contains an SQS queue resource
#       And: 'KmsMasterKeyId' is not provided
#       And: 'SqsManagedSseEnabled' is provided and set to bool(true)
#      Then: PASS

#
# Constants
#
let SQS_QUEUE_TYPE = "AWS::SQS::Queue"
let INPUT_DOCUMENT = this
#
# Assignments
#
let sqs_queues = Resources.*[ Type == %SQS_QUEUE_TYPE ]

#
# Primary Rules
#
rule sqs_queue_encrypted_check when is_cfn_template(%INPUT_DOCUMENT)
                                    %sqs_queues not empty {
    check(%sqs_queues.Properties)
        <<
        [CT.SQS.PR.2]: Require any Amazon SQS queue to have encryption at rest configured
        [FIX]: Set 'SqsManagedSseEnabled' to 'true' or set an AWS KMS key identifier in the 'KmsMasterKeyId' property.
        >>
}

rule sqs_queue_encrypted_check when is_cfn_hook(%INPUT_DOCUMENT, %SQS_QUEUE_TYPE) {
    check(%INPUT_DOCUMENT.%SQS_QUEUE_TYPE.resourceProperties)
        <<
        [CT.SQS.PR.2]: Require any Amazon SQS queue to have encryption at rest configured
        [FIX]: Set 'SqsManagedSseEnabled' to 'true' or set an AWS KMS key identifier in the 'KmsMasterKeyId' property.
        >>
}

#
# Parameterized Rules
#
rule check(sqs_queue) {
    %sqs_queue{
        check_sse_enabled(this) or
        check_kms_valid(this)
    }
}

rule check_sse_enabled(sqs_queue) {
    # Scenario 2
    SqsManagedSseEnabled exists

    # Scenario 3, 6
    KmsMasterKeyId not exists
    SqsManagedSseEnabled == true
}

rule check_kms_valid(sqs_queue) {
    # Scenario 2
    KmsMasterKeyId exists

    # Scenario 4, 5
    check_is_string_and_not_empty(KmsMasterKeyId) or
    check_local_references(%INPUT_DOCUMENT, KmsMasterKeyId, "AWS::KMS::Key") or
    check_local_references(%INPUT_DOCUMENT, KmsMasterKeyId, "AWS::KMS::Alias")

    # Scenario 5
    SqsManagedSseEnabled not exists or
    SqsManagedSseEnabled == false
}

#
# 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
}

rule check_is_string_and_not_empty(value) {
    %value {
        this is_string
        this != /\A\s*\z/
    }
}

rule check_local_references(doc, reference_properties, referenced_resource_type) {
    %reference_properties {
        "Fn::GetAtt" {
            query_for_resource(%doc, this[0], %referenced_resource_type)
                <<Local Stack reference was invalid>>
        } or Ref {
            query_for_resource(%doc, this, %referenced_resource_type)
                <<Local Stack reference was invalid>>
        }
    }
}

rule query_for_resource(doc, resource_key, referenced_resource_type) {
    let referenced_resource = %doc.Resources[ keys == %resource_key ]
    %referenced_resource not empty
    %referenced_resource {
        Type == %referenced_resource_type
    }
}
```

### CT.SQS.PR.2 example templates
<a name="ct-sqs-pr-2-templates"></a>

You can view examples of the PASS and FAIL test artifacts for the AWS Control Tower proactive controls.

PASS Example - Use this template to verify a compliant resource creation.

```
Resources:
  KMSKey:
    Type: AWS::KMS::Key
    Properties:
      KeyPolicy:
        Version: 2012-10-17		 	 	 
        Id: key-default-1
        Statement:
        - Sid: Enable IAM User Permissions
          Effect: Allow
          Principal:
            AWS: '*'
          Action: 'kms:*'
          Resource: '*'
  SQSQueue:
    Type: AWS::SQS::Queue
    Properties:
      KmsMasterKeyId:
        Ref: KMSKey
```

FAIL Example - Use this template to verify that the control prevents non-compliant resource creation.

```
Resources:
  SQSQueue:
    Type: AWS::SQS::Queue
    Properties: {}
```