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wgengine/magicsock,ipn/ipnlocal: store and load homeDERP from cache (#19491)

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With netmap caching, the home DERP of the self node was neither saved to
the cache or loaded from it, making nodes not stick to a DERP when
starting without a connection to control.

Instead, make sure that when a cache is available, load that cache,
before looking for DERP servers. This is implemented by allowing a skip
of ReSTUN in setting the DERP map (we must have a DERP map before
setting the home DERP), so the DERP from cache will set itself and be
sticky until a connection to control is established.

Making DERP only change when connected to control is handled by existing
code from f072d017bd.

Updates #19490

Signed-off-by: Claus Lensbøl <claus@tailscale.com>
This commit is contained in:
Claus Lensbøl
2026-04-29 10:24:09 -04:00
committed by GitHub
parent 1841a93ab2
commit 78627c132f
9 changed files with 493 additions and 20 deletions
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wgengine/magicsock/derp.go
+38 -7
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@@ -102,6 +102,7 @@ type activeDerp struct {
var (
pickDERPFallbackForTests func() int
reSTUNHookForTests func(why string)
)
// pickDERPFallback returns a non-zero but deterministic DERP node to
@@ -155,7 +156,7 @@ var checkControlHealthDuringNearestDERPInTests = false
// region that it selected and set (via setNearestDERP).
//
// c.mu must NOT be held.
func (c *Conn) maybeSetNearestDERP(report *netcheck.Report) (preferredDERP int) {
func (c *Conn) maybeSetNearestDERP(report *netcheck.Report, force bool) (preferredDERP int) {
// Don't change our PreferredDERP if we don't have a connection to
// control; if we don't, then we can't inform peers about a DERP home
// change, which breaks all connectivity. Even if this DERP region is
@@ -169,7 +170,10 @@ func (c *Conn) maybeSetNearestDERP(report *netcheck.Report) (preferredDERP int)
//
// Despite the above behaviour, ensure that we set the nearest DERP if
// we don't currently have one set; any DERP server is better than
// none, even if not connected to control.
// none, even if not connected to control. The exception here is if we have
// a cached netmap with a previous DERP server. Retaining the previous DERP
// makes it easier for other nodes to find each other when control is not
// available.
var connectedToControl bool
if testenv.InTest() && !checkControlHealthDuringNearestDERPInTests {
connectedToControl = true
@@ -179,7 +183,7 @@ func (c *Conn) maybeSetNearestDERP(report *netcheck.Report) (preferredDERP int)
c.mu.Lock()
myDerp := c.myDerp
c.mu.Unlock()
if !connectedToControl {
if !connectedToControl && !force {
if myDerp != 0 {
metricDERPHomeNoChangeNoControl.Add(1)
return myDerp
@@ -198,15 +202,32 @@ func (c *Conn) maybeSetNearestDERP(report *netcheck.Report) (preferredDERP int)
}
if preferredDERP != myDerp {
c.logf(
"magicsock: home DERP changing from derp-%d [%dms] to derp-%d [%dms]",
c.myDerp, report.RegionLatency[myDerp].Milliseconds(), preferredDERP, report.RegionLatency[preferredDERP].Milliseconds())
"magicsock: home DERP changing from derp-%d [%dms] to derp-%d [%dms] (forced=%t)",
c.myDerp, report.RegionLatency[myDerp].Milliseconds(), preferredDERP, report.RegionLatency[preferredDERP].Milliseconds(), force)
}
if !c.setNearestDERP(preferredDERP) {
preferredDERP = 0
} else if preferredDERP != myDerp {
c.homeDERPChangedPub.Publish(HomeDERPChanged{Old: myDerp, New: preferredDERP})
}
return
}
// HomeDERPChanged is an event sent on the [eventbus.Bus] when a new home DERP
// server has been selected. Its publisher is [magicsock.Coon]; its main
// subscriber is [ipnlocal.LocalBackend] that updates the homeDERP used by the
// netmap cache.
// TODO(cmol): Move the subscriber to not inject into localBackend, but rather
// into the netmap at the controlClient mapSession level once there is a stable
// abstraction to use.
type HomeDERPChanged struct {
Old, New int
}
func (c *Conn) ForceSetNearestDERP(regionID int) int {
return c.maybeSetNearestDERP(&netcheck.Report{PreferredDERP: regionID}, true)
}
func (c *Conn) derpRegionCodeLocked(regionID int) string {
if c.derpMap == nil {
return ""
@@ -771,7 +792,11 @@ func (c *Conn) SetOnlyTCP443(v bool) {
// SetDERPMap controls which (if any) DERP servers are used.
// A nil value means to disable DERP; it's disabled by default.
func (c *Conn) SetDERPMap(dm *tailcfg.DERPMap) {
//
// If doReStun is false, the post setting ReSTUN is not performed.
// This flag is used for setting the map from a cache to make it possible to
// also set the homeDERP from cache.
func (c *Conn) SetDERPMap(dm *tailcfg.DERPMap, doReStun bool) {
c.mu.Lock()
defer c.mu.Unlock()
@@ -828,8 +853,14 @@ func (c *Conn) SetDERPMap(dm *tailcfg.DERPMap) {
}
}
go c.ReSTUN("derp-map-update")
if doReStun {
if reSTUNHookForTests != nil {
reSTUNHookForTests("derp-map-update")
}
go c.ReSTUN("derp-map-update")
}
}
func (c *Conn) wantDerpLocked() bool { return c.derpMap != nil }
// c.mu must be held.