SecurityGroup

Creates an Amazon EC2 security group within a VPC. Security Groups act like a firewall with a set of rules, and are associated with any AWS resource that has or creates Elastic Network Interfaces (ENIs). A typical example of a resource that has a security group is an Instance (or Auto Scaling Group of instances) If you are defining new infrastructure in CDK, there is a good chance you won't have to interact with this class at all. Like IAM Roles, Security Groups need to exist to control access between AWS resources, but CDK will automatically generate and populate them with least-privilege permissions for you so you can concentrate on your business logic. All Constructs that require Security Groups will create one for you if you don't specify one at construction. After construction, you can selectively allow connections to and between constructs via--for example-- the `instance.connections` object. Think of it as "allowing connections to your instance", rather than "adding ingress rules a security group". See the [Allowing Connections](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-cdk-lib.aws_ec2-readme.html#allowing-connections) section in the library documentation for examples. Direct manipulation of the Security Group through `addIngressRule` and `addEgressRule` is possible, but mutation through the `.connections` object is recommended. If you peer two constructs with security groups this way, appropriate rules will be created in both. If you have an existing security group you want to use in your CDK application, you would import it like this: ```ts const securityGroup = ec2.SecurityGroup.fromSecurityGroupId(this, 'SG', 'sg-12345', { mutable: false }); ```