code: func (c *Cloud) findVPCID() (string, error) {
  	macs, err := c.metadata.GetMetadata("network/interfaces/macs/")
  	if err != nil {
  		return "", fmt.Errorf("Could not list interfaces of the instance: %q", err)
  	}
  
  	// loop over interfaces, first vpc id returned wins
  	for _, macPath := range strings.Split(macs, "\n") {
  		if len(macPath) == 0 {
  			continue
  		}
  		url := fmt.Sprintf("network/interfaces/macs/%svpc-id", macPath)
  		vpcID, err := c.metadata.GetMetadata(url)
  		if err != nil {
  			continue
  		}
  		return vpcID, nil
  	}
  	return "", fmt.Errorf("Could not find VPC ID in instance metadata")
  }
docs: // Retrieves instance's vpc id from metadata