code: func (agent *ecsAgent) setVPCSubnet() (error, bool) {
  	mac, err := agent.ec2MetadataClient.PrimaryENIMAC()
  	if err != nil {
  		return fmt.Errorf("unable to get mac address of instance's primary ENI from instance metadata: %v", err), false
  	}
  
  	vpcID, err := agent.ec2MetadataClient.VPCID(mac)
  	if err != nil {
  		if isInstanceLaunchedInVPC(err) {
  			return fmt.Errorf("unable to get vpc id from instance metadata: %v", err), true
  		}
  		return instanceNotLaunchedInVPCError, false
  	}
  
  	subnetID, err := agent.ec2MetadataClient.SubnetID(mac)
  	if err != nil {
  		return fmt.Errorf("unable to get subnet id from instance metadata: %v", err), false
  	}
  	agent.vpc = vpcID
  	agent.subnet = subnetID
  	agent.mac = mac
  	return nil, false
  }
docs: // setVPCSubnet sets the vpc and subnet ids for the agent by querying the
  // instance metadata service