EC2 instance blocks Internet ingress to MySQL port 3306

# Restrict MySQL (3306) from Internet
resource "aws_security_group" "<example_resource_name>" {
  name   = "<example_resource_name>"
  vpc_id = "<example_resource_id>"

  ingress {
    from_port   = 3306
    to_port     = 3306
    protocol    = "tcp"
    cidr_blocks = ["10.0.0.0/8"] # Critical: do NOT use 0.0.0.0/0; restrict 3306 to a private CIDR
  }
}

# CloudFormation: restrict MySQL (3306) from Internet
Resources:
  <example_resource_name>:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Restrict MySQL access
      VpcId: <example_resource_id>
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 3306
          ToPort: 3306
          CidrIp: 10.0.0.0/8  # Critical: do NOT use 0.0.0.0/0; restrict 3306 to a private range