func (a *Allocator) taskCreateNetworkAttachments(t *api.Task, s *api.Service) {
	// If task network attachments have already been filled in no
	// need to do anything else.
	if len(t.Networks) != 0 {
		return
	}

	var networks []*api.NetworkAttachment
	if isIngressNetworkNeeded(s) {
		networks = append(networks, &api.NetworkAttachment{Network: a.netCtx.ingressNetwork})
	}

	a.store.View(func(tx store.ReadTx) {
		// Always prefer NetworkAttachmentConfig in the TaskSpec
		specNetworks := t.Spec.Networks
		if len(specNetworks) == 0 && s != nil && len(s.Spec.Networks) != 0 {
			specNetworks = s.Spec.Networks
		}

		for _, na := range specNetworks {
			n := store.GetNetwork(tx, na.Target)
			if n == nil {
				continue
			}

			attachment := api.NetworkAttachment{Network: n}
			attachment.Aliases = append(attachment.Aliases, na.Aliases...)
			attachment.Addresses = append(attachment.Addresses, na.Addresses...)

			networks = append(networks, &attachment)
		}
	})

	taskUpdateNetworks(t, networks)
}

// allocate the IP addresses for a single network attachment of the task.
func (na *NetworkAllocator) allocateNetworkIPs(nAttach *api.NetworkAttachment) error {
	var ip *net.IPNet

	ipam, _, _, err := na.resolveIPAM(nAttach.Network)
	if err != nil {
		return errors.Wrap(err, "failed to resolve IPAM while allocating")
	}

	localNet := na.getNetwork(nAttach.Network.ID)
	if localNet == nil {
		return fmt.Errorf("could not find network allocator state for network %s", nAttach.Network.ID)
	}

	addresses := nAttach.Addresses
	if len(addresses) == 0 {
		addresses = []string{""}
	}

	for i, rawAddr := range addresses {
		var addr net.IP
		if rawAddr != "" {
			var err error
			addr, _, err = net.ParseCIDR(rawAddr)
			if err != nil {
				addr = net.ParseIP(rawAddr)

				if addr == nil {
					return errors.Wrapf(err, "could not parse address string %s", rawAddr)
				}
			}
		}

		for _, poolID := range localNet.pools {
			var err error

			ip, _, err = ipam.RequestAddress(poolID, addr, nil)
			if err != nil && err != ipamapi.ErrNoAvailableIPs && err != ipamapi.ErrIPOutOfRange {
				return errors.Wrap(err, "could not allocate IP from IPAM")
			}

			// If we got an address then we are done.
			if err == nil {
				ipStr := ip.String()
				localNet.endpoints[ipStr] = poolID
				addresses[i] = ipStr
				nAttach.Addresses = addresses
				return nil
			}
		}
	}

	return errors.New("could not find an available IP")
}

func (a *Allocator) taskCreateNetworkAttachments(t *api.Task, s *api.Service) {
	// If task network attachments have already been filled in no
	// need to do anything else.
	if len(t.Networks) != 0 {
		return
	}

	var networks []*api.NetworkAttachment

	// The service to which this task belongs is trying to expose
	// ports to the external world. Automatically attach the task
	// to the ingress network.
	if s != nil && s.Spec.Endpoint != nil && len(s.Spec.Endpoint.Ports) != 0 {
		networks = append(networks, &api.NetworkAttachment{Network: a.netCtx.ingressNetwork})
	}

	a.store.View(func(tx store.ReadTx) {
		// Always prefer NetworkAttachmentConfig in the TaskSpec
		specNetworks := t.Spec.Networks
		if len(specNetworks) == 0 && s != nil && len(s.Spec.Networks) != 0 {
			specNetworks = s.Spec.Networks
		}

		for _, na := range specNetworks {
			n := store.GetNetwork(tx, na.Target)
			if n == nil {
				continue
			}

			attachment := api.NetworkAttachment{Network: n}
			attachment.Aliases = append(attachment.Aliases, na.Aliases...)
			attachment.Addresses = append(attachment.Addresses, na.Addresses...)

			networks = append(networks, &attachment)
		}
	})

	taskUpdateNetworks(t, networks)
}