AWS Lambda template

The following template uses an AWS Lambda (Lambda) function and custom resource to append a new security group to a list of existing security groups. This function is useful when you want to build a list of security groups dynamically, so that your list includes both new and existing security groups. For example, you can pass a list of existing security groups as a parameter value, append the new value to the list, and then associate all your values with an EC2 instance. For more information about the Lambda function resource type, see AWS::Lambda::Function.

In the example, when CloudFormation creates the AllSecurityGroups custom resource, CloudFormation invokes the AppendItemToListFunction Lambda function. CloudFormation passes the list of existing security groups and a new security group (NewSecurityGroup) to the function, which appends the new security group to the list and then returns the modified list. CloudFormation uses the modified list to associate all security groups with the MyEC2Instance resource.

JSON

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Parameters": {
        "ExistingSecurityGroups": {
            "Type": "List<AWS::EC2::SecurityGroup::Id>"
        },
        "ExistingVPC": {
            "Type": "AWS::EC2::VPC::Id",
            "Description": "The VPC ID that includes the security groups in the ExistingSecurityGroups parameter."
        },
        "InstanceType": {
            "Type": "String",
            "Default": "t2.micro",
            "AllowedValues": [
                "t2.micro",
                "t3.micro"
            ]
        }
    },

    "Resources": {
        "SecurityGroup": {
            "Type": "AWS::EC2::SecurityGroup",
            "Properties": {
                "GroupDescription": "Allow HTTP traffic to the host",
                "VpcId": {
                    "Ref": "ExistingVPC"
                },
                "SecurityGroupIngress": [
                    {
                        "IpProtocol": "tcp",
                        "FromPort": 80,
                        "ToPort": 80,
                        "CidrIp": "0.0.0.0/0"
                    }
                ],
                "SecurityGroupEgress": [
                    {
                        "IpProtocol": "tcp",
                        "FromPort": 80,
                        "ToPort": 80,
                        "CidrIp": "0.0.0.0/0"
                    }
                ]
            }
        },
        "AllSecurityGroups": {
            "Type": "Custom::Split",
            "Properties": {
                "ServiceToken": {
                    "Fn::GetAtt": [
                        "AppendItemToListFunction",
                        "Arn"
                    ]
                },
                "List": {
                    "Ref": "ExistingSecurityGroups"
                },
                "AppendedItem": {
                    "Ref": "SecurityGroup"
                }
            }
        },
        "AppendItemToListFunction": {
            "Type": "AWS::Lambda::Function",
            "Properties": {
                "Handler": "index.handler",
                "Role": {
                    "Fn::GetAtt": [
                        "LambdaExecutionRole",
                        "Arn"
                    ]
                },
                "Code": {
                    "ZipFile": {
                        "Fn::Join": [
                            "",
                            [
                                "var response = require('cfn-response');",
                                "exports.handler = function(event, context) {",
                                "   var responseData = {Value: event.ResourceProperties.List};",
                                "   responseData.Value.push(event.ResourceProperties.AppendedItem);",
                                "   response.send(event, context, response.SUCCESS, responseData);",
                                "};"
                            ]
                        ]
                    }
                },
                "Runtime": "nodejs20.x"
            }
        },
        "MyEC2Instance": {
            "Type": "AWS::EC2::Instance",
            "Properties": {
                "ImageId": "{{resolve:ssm:/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2}}",
                "SecurityGroupIds": {
                    "Fn::GetAtt": [
                        "AllSecurityGroups",
                        "Value"
                    ]
                },
                "InstanceType": {
                    "Ref": "InstanceType"
                }
            }
        },
        "LambdaExecutionRole": {
            "Type": "AWS::IAM::Role",
            "Properties": {
                "AssumeRolePolicyDocument": {
                    "Version": "2012-10-17", 		 	 	 
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Principal": {
                                "Service": [
                                    "lambda.amazonaws.com"
                                ]
                            },
                            "Action": [
                                "sts:AssumeRole"
                            ]
                        }
                    ]
                },
                "Path": "/",
                "Policies": [
                    {
                        "PolicyName": "root",
                        "PolicyDocument": {
                            "Version": "2012-10-17", 		 	 	 
                            "Statement": [
                                {
                                    "Effect": "Allow",
                                    "Action": [
                                        "logs:*"
                                    ],
                                    "Resource": "arn:aws:logs:*:*:*"
                                }
                            ]
                        }
                    }
                ]
            }
        }
    },
    "Outputs": {
        "AllSecurityGroups": {
            "Description": "Security Groups that are associated with the EC2 instance",
            "Value": {
                "Fn::Join": [
                    ", ",
                    {
                        "Fn::GetAtt": [
                            "AllSecurityGroups",
                            "Value"
                        ]
                    }
                ]
            }
        }
    }
}

YAML

AWSTemplateFormatVersion: '2010-09-09'
Parameters:
  ExistingSecurityGroups:
    Type: List<AWS::EC2::SecurityGroup::Id>
  ExistingVPC:
    Type: AWS::EC2::VPC::Id
    Description: The VPC ID that includes the security groups in the ExistingSecurityGroups parameter.
  InstanceType:
    Type: String
    Default: t2.micro
    AllowedValues:
      - t2.micro
      - t3.micro
Resources:
  SecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow HTTP traffic to the host
      VpcId: !Ref ExistingVPC
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0
      SecurityGroupEgress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0
  AllSecurityGroups:
    Type: Custom::Split
    Properties:
      ServiceToken: !GetAtt AppendItemToListFunction.Arn
      List: !Ref ExistingSecurityGroups
      AppendedItem: !Ref SecurityGroup
  AppendItemToListFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        ZipFile: !Join
          - ''
          - - var response = require('cfn-response');
            - exports.handler = function(event, context) {
            - '   var responseData = {Value: event.ResourceProperties.List};'
            - '   responseData.Value.push(event.ResourceProperties.AppendedItem);'
            - '   response.send(event, context, response.SUCCESS, responseData);'
            - '};'
      Runtime: nodejs20.x
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: '{{resolve:ssm:/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2}}'
      SecurityGroupIds: !GetAtt AllSecurityGroups.Value
      InstanceType: !Ref InstanceType
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17' 		 	 	 
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
            Action:
              - sts:AssumeRole
      Path: /
      Policies:
        - PolicyName: root
          PolicyDocument:
            Version: '2012-10-17' 		 	 	 
            Statement:
              - Effect: Allow
                Action:
                  - logs:*
                Resource: arn:aws:logs:*:*:*
Outputs:
  AllSecurityGroups:
    Description: Security Groups that are associated with the EC2 instance
    Value: !Join
      - ', '
      - !GetAtt AllSecurityGroups.Value