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fix(rest-api): reuse unchanged instance interfaces #5014

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790d18f
fix(rest-api): reuse unchanged instance interfaces
hwadekar-nv Aug 14, 2026
ff36a85
Addressed review comments by cr
hwadekar-nv Aug 14, 2026
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92 changes: 75 additions & 17 deletions rest-api/api/pkg/api/handler/instance.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2581,8 +2581,8 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
// Collect all Subnet and VPC Prefix IDs for batch query
subnetIDs := []uuid.UUID{}
vpcPrefixIDs := []uuid.UUID{}
subnetIfcMap := map[uuid.UUID]int{}
vpcPrefixIfcMap := map[uuid.UUID]int{}
subnetIfcMap := map[uuid.UUID]uint64{}
vpcPrefixIfcMap := map[uuid.UUID]uint64{}

for _, ifc := range apiRequest.Interfaces {
if ifc.SubnetID != nil {
Expand Down Expand Up @@ -2638,8 +2638,8 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
return cutil.NewAPIErrorResponse(c, interfaceVpcErr.Code, interfaceVpcErr.Message, interfaceVpcErr.Data)
}

existingSubnetIfcMap := map[uuid.UUID]int{}
existingVpcPrefixIfcMap := map[uuid.UUID]int{}
existingSubnetIfcMap := map[uuid.UUID]uint64{}
existingVpcPrefixIfcMap := map[uuid.UUID]uint64{}
if len(apiRequest.Interfaces) > 0 {
ifcDAO := cdbm.NewInterfaceDAO(uih.dbSession)
existingIfcsForCapacity, _, err := ifcDAO.GetAll(ctx, nil, cdbm.InterfaceFilterInput{InstanceIDs: []uuid.UUID{instance.ID}}, cdbp.PageInput{Limit: cutil.GetPtr(cdbp.TotalLimit)}, nil)
Expand All @@ -2649,6 +2649,10 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
}
for i := range existingIfcsForCapacity {
eifc := &existingIfcsForCapacity[i]
if eifc.Status == cdbm.InterfaceStatusDeleting {
continue
}

if eifc.SubnetID != nil {
existingSubnetIfcMap[*eifc.SubnetID]++
}
Expand Down Expand Up @@ -2742,9 +2746,13 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
}

// Check if Subnet is exhausted
incomingInterfaceIPs := subnetIfcMap[subnetID] - existingSubnetIfcMap[subnetID]
incomingInterfaceIPs := uint64(0)
if subnetIfcMap[subnetID] > existingSubnetIfcMap[subnetID] {
incomingInterfaceIPs = subnetIfcMap[subnetID] - existingSubnetIfcMap[subnetID]
}

subnetUsage := subnetUsageMap[subnetID]
if subnetUsage != nil && subnetUsage.AvailableIPs > 0 && subnetUsage.AcquiredIPs+uint64(incomingInterfaceIPs) > subnetUsage.AvailableIPs {
if incomingInterfaceIPs > 0 && subnetUsage != nil && subnetUsage.AvailableIPs > 0 && subnetUsage.AcquiredIPs+incomingInterfaceIPs > subnetUsage.AvailableIPs {
msg := fmt.Sprintf(
"Subnet %v does not have enough IP addresses: %d of %d IP addresses remain available, but the %d additional interface(s) in this request require %d IP address(es)",
subnetID, subnetUsage.AvailableIPs-subnetUsage.AcquiredIPs, subnetUsage.AvailableIPs, incomingInterfaceIPs, incomingInterfaceIPs,
Expand Down Expand Up @@ -2826,9 +2834,13 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
}

// Check if VPC Prefix is exhausted
incomingInterfaceIPs := max(vpcPrefixIfcMap[vpcPrefixID]-existingVpcPrefixIfcMap[vpcPrefixID], 0)
incomingInterfaceIPs := uint64(0)
if vpcPrefixIfcMap[vpcPrefixID] > existingVpcPrefixIfcMap[vpcPrefixID] {
incomingInterfaceIPs = vpcPrefixIfcMap[vpcPrefixID] - existingVpcPrefixIfcMap[vpcPrefixID]
}

vpUsage := vpcPrefixUsageMap[vpcPrefixID]
if vpUsage != nil && vpUsage.AvailableIPs > 0 && vpUsage.AcquiredIPs+uint64(incomingInterfaceIPs)*2 > vpUsage.AvailableIPs {
if incomingInterfaceIPs > 0 && vpUsage != nil && vpUsage.AvailableIPs > 0 && vpUsage.AcquiredIPs+incomingInterfaceIPs*2 > vpUsage.AvailableIPs {
msg := fmt.Sprintf(
"VPC Prefix %v does not have enough IP addresses: %d of %d IP addresses remain available, but the %d additional interface(s) in this request require %d IP addresses",
vpcPrefixID, vpUsage.AvailableIPs-vpUsage.AcquiredIPs, vpUsage.AvailableIPs, incomingInterfaceIPs, incomingInterfaceIPs*2,
Expand Down Expand Up @@ -3460,8 +3472,8 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
// return an empty list. Reads after this should reflect the
// auto contract (no explicit interfaces) rather than the
// stale rows that pre-dated the mode switch.
// - Explicit interfaces in the request: create the new rows
// and mark the previous rows as Deleting (existing behavior).
// - Explicit interfaces in the request: reuse matching rows,
// create new rows, and mark only removed rows as Deleting.
// - Neither (no interface change, not switching to auto):
// carry the existing rows forward.
switch {
Expand All @@ -3476,7 +3488,36 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
}
newdbIfcs = []cdbm.Interface{}
case len(apiRequest.Interfaces) > 0:
existingIfcMap := make(map[cdbm.EthernetInterfaceKey][]cdbm.Interface)

for existingIfcIndex := range existingIfcs {
if existingIfcs[existingIfcIndex].Status == cdbm.InterfaceStatusDeleting {
continue
}

key := existingIfcs[existingIfcIndex].EthernetKey()
existingIfcMap[key] = append(existingIfcMap[key], existingIfcs[existingIfcIndex])
}

reusedIfcIDs := make(map[uuid.UUID]struct{})
for _, dbifc := range dbInterfaces {
key := dbifc.EthernetKey()

existingIfcsForKey := existingIfcMap[key]
if len(existingIfcsForKey) > 0 {
reusedIfc := existingIfcsForKey[0]
if len(existingIfcsForKey) == 1 {
delete(existingIfcMap, key)
} else {
existingIfcMap[key] = existingIfcsForKey[1:]
}

reusedIfcIDs[reusedIfc.ID] = struct{}{}
newdbIfcs = append(newdbIfcs, reusedIfc)

continue
}

input := cdbm.InterfaceCreateInput{
InstanceID: instance.ID,
SubnetID: dbifc.SubnetID,
Expand All @@ -3502,19 +3543,36 @@ func (uih UpdateInstanceHandler) Handle(c echo.Context) error {
ifc := *newDbifc
ifc.Vpc = dbifc.Vpc
ifc.VpcPrefix = dbifc.VpcPrefix // We created the interface in the DB based on the values in dbifc, so we can populate this as well.
ifc.Subnet = dbifc.Subnet
// Add the new Interface to the list of new Interfaces
newdbIfcs = append(newdbIfcs, ifc)
}

// Update status of existing Interfaces to Deleting
for i := range existingIfcs {
existingIfcs[i].Status = cdbm.InterfaceStatusDeleting
_, err := ifcDAO.Update(ctx, tx, cdbm.InterfaceUpdateInput{InterfaceID: existingIfcs[i].ID, Status: cutil.GetPtr(cdbm.InterfaceStatusDeleting)})
if err != nil {
logger.Error().Err(err).Msg("failed to update Interface record in DB")
return cutil.NewAPIError(http.StatusInternalServerError, "Failed to update Interface for Instance, DB error", nil)
unmatchedIfcs := make([]cdbm.Interface, 0, len(existingIfcs)-len(reusedIfcIDs))
for existingIfcIndex := range existingIfcs {
if _, reused := reusedIfcIDs[existingIfcs[existingIfcIndex].ID]; reused {
continue
}

if existingIfcs[existingIfcIndex].Status != cdbm.InterfaceStatusDeleting {
existingIfcs[existingIfcIndex].Status = cdbm.InterfaceStatusDeleting

// Deleting rows retain their associations and allocated addresses until Site cleanup releases them.
_, err := ifcDAO.Update(ctx, tx, cdbm.InterfaceUpdateInput{
InterfaceID: existingIfcs[existingIfcIndex].ID,
Status: cutil.GetPtr(cdbm.InterfaceStatusDeleting),
}) //nolint:exhaustruct // Only the lifecycle status changes; associations remain held.
if err != nil {
logger.Error().Err(err).Msg("failed to update Interface record in DB")

return cutil.NewAPIError(http.StatusInternalServerError, "Failed to update Interface for Instance, DB error", nil)
}
}

unmatchedIfcs = append(unmatchedIfcs, existingIfcs[existingIfcIndex])
}

existingIfcs = unmatchedIfcs
default:
newdbIfcs = existingIfcs
}
Expand Down
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