cmd/cli: always rebootstrap when check upstream

Otherwise, network changes may not be seen on some platforms, causing
ctrld failed to recover and failing all requests.

While at it, also doing the check DNS in separate goroutine, prevent it
from blocking ctrld from notifying others that it "started". The issue
was seen when ctrld is configured as direct listener, requests are
flooded before ctrld started, causing the healtch process failed.

cmd/cli/loop.go

@@ -56,7 +56,10 @@ func (p *prog) checkDnsLoop() {
 	mainLog.Load().Debug().Msg("start checking DNS loop")
 	upstream := make(map[string]*ctrld.UpstreamConfig)
 	p.loopMu.Lock()
-	for _, uc := range p.cfg.Upstream {
+	for n, uc := range p.cfg.Upstream {
+		if p.um.isDown("upstream." + n) {
+			continue
+		}
 		uid := uc.UID()
 		p.loop[uid] = false
 		upstream[uid] = uc

cmd/cli/prog.go

@@ -282,14 +282,14 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 		}
 	}
 
-	// Check for possible DNS loop.
-	p.checkDnsLoop()
 	close(p.onStartedDone)
 
-	// Start check DNS loop ticker.
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
+		// Check for possible DNS loop.
+		p.checkDnsLoop()
+		// Start check DNS loop ticker.
 		p.checkDnsLoopTicker(ctx)
 	}()
 

cmd/cli/upstream_monitor.go

@@ -7,7 +7,6 @@ import (
 	"time"
 
 	"github.com/miekg/dns"
-	"tailscale.com/logtail/backoff"
 
 	"github.com/Control-D-Inc/ctrld"
 )
@@ -15,8 +14,8 @@ import (
 const (
 	// maxFailureRequest is the maximum failed queries allowed before an upstream is marked as down.
 	maxFailureRequest = 100
-	// checkUpstreamMaxBackoff is the max backoff time when checking upstream status.
+	// checkUpstreamBackoffSleep is the time interval between each upstream checks.
-	checkUpstreamMaxBackoff = 2 * time.Minute
+	checkUpstreamBackoffSleep = 2 * time.Second
 )
 
 // upstreamMonitor performs monitoring upstreams health.
@@ -76,7 +75,6 @@ func (um *upstreamMonitor) checkUpstream(upstream string, uc *ctrld.UpstreamConf
 	um.checking[upstream] = true
 	um.mu.Unlock()
 
-	bo := backoff.NewBackoff("checkUpstream", logf, checkUpstreamMaxBackoff)
 	resolver, err := ctrld.NewResolver(uc)
 	if err != nil {
 		mainLog.Load().Warn().Err(err).Msg("could not check upstream")
@@ -84,15 +82,20 @@ func (um *upstreamMonitor) checkUpstream(upstream string, uc *ctrld.UpstreamConf
 	}
 	msg := new(dns.Msg)
 	msg.SetQuestion(".", dns.TypeNS)
-	ctx := context.Background()
 
-	for {
+	check := func() error {
+		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		uc.ReBootstrap()
 		_, err := resolver.Resolve(ctx, msg)
-		if err == nil {
+		return err
+	}
+	for {
+		if err := check(); err == nil {
 			mainLog.Load().Debug().Msgf("upstream %q is online", uc.Endpoint)
 			um.reset(upstream)
 			return
 		}
-		bo.BackOff(ctx, err)
+		time.Sleep(checkUpstreamBackoffSleep)
 	}
 }