Adding an existing security group CloudFormation EC2 template

Question

Instead of having to set ingress and egress rules, how do I reference existing EC2 security groups in a CloudFormation Template?

 Resources: EC2Instance: Type: AWS::EC2::Instance Properties: InstanceType: Ref: InstanceType SecurityGroups: - Ref: InstanceSecurityGroup KeyName: Ref: KeyName ImageId: Fn::FindInMap: - AWSRegionArch2AMI - Ref: AWS::Region - Fn::FindInMap: - AWSInstanceType2Arch - Ref: InstanceType - Arch InstanceSecurityGroup: Type: AWS::EC2::SecurityGroup Properties: GroupDescription: Existing Groups SecurityGroupIds: - Ref: sg-12345 - Ref: sg-12312 

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 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 

Answer 1

To do this you just add them in your EC2 Resource property directly under SecurityGroupIds:

Resources: EC2Instance: Type: AWS::EC2::Instance Properties: InstanceType: Ref: InstanceType SecurityGroupIds: - sg-12345 - sg-12312 KeyName: Ref: KeyName ImageId: Fn::FindInMap: - AWSRegionArch2AMI - Ref: AWS::Region - Fn::FindInMap: - AWSInstanceType2Arch - Ref: InstanceType - Arch