在CloudFormation模板中指定正确的VPC和安全组。例如：

Resources:
  EC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: ami-0c55b159cbfafe1f0
      InstanceType: t2.micro
      NetworkInterfaces:
      - GroupSet:
        - Ref: SecurityGroup
        AssociatePublicIpAddress: 'true'
        DeviceIndex: '0'
        DeleteOnTermination: 'true'
        SubnetId: subnet-0123456789abcdef
  SecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow SSH and HTTP access
      SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: '22'
        ToPort: '22'
        CidrIp: 0.0.0.0/0
      - IpProtocol: tcp
        FromPort: '80'
        ToPort: '80'
        CidrIp: 0.0.0.0/0
      VpcId: vpc-0123456789abcdef