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ipn/ipnlocal: improve sticky last suggestion

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The last suggested exit node needs to be incorporated in the decision
making process when a new suggestion is requested, but currently it is
not quite right: it'll be used if the suggestion code has an error or a
netmap is unavailable, but it won't be used otherwise.

Instead, this makes the last suggestion into a tiebreaker when making a
random selection between equally-good options. If the last suggestion
does not make it to the final selection pool, then a different
suggestion will be made.

Since LocalBackend.SuggestExitNode is back to being a thin shim that
sets up the parameters to suggestExitNode, it no longer needs a test.
Its test was unable to be comprehensive anyway as the code being tested
contains an uncontrolled random number generator.

Updates tailscale/corp#19681

Change-Id: I94ecc9a0d1b622de3df4ef90523f1d3e67b4bfba
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
This commit is contained in:
Adrian Dewhurst
2024-05-31 09:54:46 -04:00
committed by Adrian Dewhurst
parent 7a7e314096
commit 0219317372
2 changed files with 35 additions and 535 deletions
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75
ipn/ipnlocal/local.go
View File

@@ -154,12 +154,6 @@ type watchSession struct {
sessionID string
}
// lastSuggestedExitNode stores the last suggested exit node ID and name in local backend.
type lastSuggestedExitNode struct {
id tailcfg.StableNodeID
name string
}
// LocalBackend is the glue between the major pieces of the Tailscale
// network software: the cloud control plane (via controlclient), the
// network data plane (via wgengine), and the user-facing UIs and CLIs
@@ -340,9 +334,9 @@ type LocalBackend struct {
// outgoingFiles keeps track of Taildrop outgoing files keyed to their OutgoingFile.ID
outgoingFiles map[string]*ipn.OutgoingFile
// lastSuggestedExitNode stores the last suggested exit node ID and name.
// lastSuggestedExitNode updates whenever the suggestion changes.
lastSuggestedExitNode lastSuggestedExitNode
// lastSuggestedExitNode stores the last suggested exit node suggestion to
// avoid unnecessary churn between multiple equally-good options.
lastSuggestedExitNode tailcfg.StableNodeID
}
// HealthTracker returns the health tracker for the backend.
@@ -6047,8 +6041,8 @@ func (b *LocalBackend) resetForProfileChangeLockedOnEntry(unlock unlockOnce) err
}
b.lastServeConfJSON = mem.B(nil)
b.serveConfig = ipn.ServeConfigView{}
b.lastSuggestedExitNode = lastSuggestedExitNode{} // Reset last suggested exit node.
b.enterStateLockedOnEntry(ipn.NoState, unlock) // Reset state; releases b.mu
b.lastSuggestedExitNode = ""
b.enterStateLockedOnEntry(ipn.NoState, unlock) // Reset state; releases b.mu
b.health.SetLocalLogConfigHealth(nil)
return b.Start(ipn.Options{})
}
@@ -6425,7 +6419,6 @@ func mayDeref[T any](p *T) (v T) {
var ErrNoPreferredDERP = errors.New("no preferred DERP, try again later")
var ErrCannotSuggestExitNode = errors.New("unable to suggest an exit node, try again later")
var ErrUnableToSuggestLastExitNode = errors.New("unable to suggest last exit node")
// SuggestExitNode computes a suggestion based on the current netmap and last netcheck report. If
// there are multiple equally good options, one is selected at random, so the result is not stable. To be
@@ -6438,27 +6431,15 @@ func (b *LocalBackend) SuggestExitNode() (response apitype.ExitNodeSuggestionRes
b.mu.Lock()
lastReport := b.MagicConn().GetLastNetcheckReport(b.ctx)
netMap := b.netMap
lastSuggestedExitNode := b.lastSuggestedExitNode
prevSuggestion := b.lastSuggestedExitNode
b.mu.Unlock()
if lastReport == nil || netMap == nil {
last, err := lastSuggestedExitNode.asAPIType()
if err != nil {
return response, ErrCannotSuggestExitNode
}
return last, err
}
res, err := suggestExitNode(lastReport, netMap, randomRegion, randomNode, getAllowedSuggestions())
res, err := suggestExitNode(lastReport, netMap, prevSuggestion, randomRegion, randomNode, getAllowedSuggestions())
if err != nil {
last, err := lastSuggestedExitNode.asAPIType()
if err != nil {
return response, ErrCannotSuggestExitNode
}
return last, err
return res, err
}
b.mu.Lock()
b.lastSuggestedExitNode.id = res.ID
b.lastSuggestedExitNode.name = res.Name
b.lastSuggestedExitNode = res.ID
b.mu.Unlock()
return res, err
}
@@ -6467,20 +6448,10 @@ func (b *LocalBackend) SuggestExitNode() (response apitype.ExitNodeSuggestionRes
// The value is returned, not the slice index.
type selectRegionFunc func(views.Slice[int]) int
// selectNodeFunc returns a node from the slice of candidate nodes.
type selectNodeFunc func(nodes views.Slice[tailcfg.NodeView]) tailcfg.NodeView
// asAPIType formats a response with the last suggested exit node's ID and name.
// Returns error if there is no id or name.
// Used as a fallback before returning a nil response and error.
func (n lastSuggestedExitNode) asAPIType() (res apitype.ExitNodeSuggestionResponse, _ error) {
if n.id != "" && n.name != "" {
res.ID = n.id
res.Name = n.name
return res, nil
}
return res, ErrUnableToSuggestLastExitNode
}
// selectNodeFunc returns a node from the slice of candidate nodes. The last
// selected node is provided for when that information is needed to make a better
// choice.
type selectNodeFunc func(nodes views.Slice[tailcfg.NodeView], last tailcfg.StableNodeID) tailcfg.NodeView
var getAllowedSuggestions = lazy.SyncFunc(fillAllowedSuggestions)
@@ -6500,7 +6471,7 @@ func fillAllowedSuggestions() set.Set[tailcfg.StableNodeID] {
return s
}
func suggestExitNode(report *netcheck.Report, netMap *netmap.NetworkMap, selectRegion selectRegionFunc, selectNode selectNodeFunc, allowList set.Set[tailcfg.StableNodeID]) (res apitype.ExitNodeSuggestionResponse, err error) {
func suggestExitNode(report *netcheck.Report, netMap *netmap.NetworkMap, prevSuggestion tailcfg.StableNodeID, selectRegion selectRegionFunc, selectNode selectNodeFunc, allowList set.Set[tailcfg.StableNodeID]) (res apitype.ExitNodeSuggestionResponse, err error) {
if report.PreferredDERP == 0 || netMap == nil || netMap.DERPMap == nil {
return res, ErrNoPreferredDERP
}
@@ -6587,7 +6558,7 @@ func suggestExitNode(report *netcheck.Report, netMap *netmap.NetworkMap, selectR
if !ok {
return res, errors.New("no candidates in expected region: this is a bug")
}
chosen := selectNode(views.SliceOf(regionCandidates))
chosen := selectNode(views.SliceOf(regionCandidates), prevSuggestion)
res.ID = chosen.StableID()
res.Name = chosen.Name()
if hi := chosen.Hostinfo(); hi.Valid() {
@@ -6614,7 +6585,7 @@ func suggestExitNode(report *netcheck.Report, netMap *netmap.NetworkMap, selectR
}
}
bestCandidates := pickWeighted(pickFrom)
chosen := selectNode(views.SliceOf(bestCandidates))
chosen := selectNode(views.SliceOf(bestCandidates), prevSuggestion)
if !chosen.Valid() {
return res, errors.New("chosen candidate invalid: this is a bug")
}
@@ -6655,8 +6626,18 @@ func randomRegion(regions views.Slice[int]) int {
return regions.At(rand.IntN(regions.Len()))
}
// randomNode is a selectNodeFunc that returns a uniformly random node.
func randomNode(nodes views.Slice[tailcfg.NodeView]) tailcfg.NodeView {
// randomNode is a selectNodeFunc that will return the node matching prefer if
// present, otherwise a uniformly random node will be selected.
func randomNode(nodes views.Slice[tailcfg.NodeView], prefer tailcfg.StableNodeID) tailcfg.NodeView {
if !prefer.IsZero() {
for i := range nodes.Len() {
nv := nodes.At(i)
if nv.StableID() == prefer {
return nv
}
}
}
return nodes.At(rand.IntN(nodes.Len()))
}