1. 在实例化 TaskDefinition 时，将 taskSubnets 属性设置为所需的子网数组，如下所示：

const taskDefinition = new ecs.TaskDefinition(this, 'taskdef', {
  compatibility: ecs.Compatibility.EC2,
  taskRole: props.taskRole,
  executionRole: props.executionRole,
  networkMode: ecs.NetworkMode.BRIDGE,
  cpu: '256',
  memoryMiB: '512',
  family: `${props.environmentPrefix}-${props.serviceName}`,
  taskSubnets: { subnetType: ec2.SubnetType.PRIVATE }
});

2. 使用 ECSService 将任务定义分配给服务时，将 vpcSubnets 属性设置为所需的子网数组，如下所示：

const service = new ecs.Ec2Service(this, 'service', {
  cluster: props.cluster,
  taskDefinition: taskDefinition,
  desiredCount: props.desiredCount,
  securityGroup: props.securityGroup,
  vpcSubnets: [{ subnetType: ec2.SubnetType.PRIVATE }],
  serviceName: `${props.environmentPrefix}-${props.serviceName}`,
  propagateTags: ecs.PropagatedTagSource.SERVICE,
});

使用上述方法设置任务和服务的子网将确保在启动任务时使用正确的子网。