Parameterize config watcher loop speed

This loop spins really quickly otherwise. This will allow cluster
operators to choose how quickly the thin plugin reconciles the
kubeconfig in the event of a stale service account token.

Signed-off-by: Connor Kuehl <connor.kuehl@suse.com>

cmd/thin_entrypoint/main.go

@@ -57,6 +57,7 @@ type Options struct {
 	AdditionalBinDir         string
 	ForceCNIVersion          bool
 	SkipTLSVerify            bool
+	WatchTimer               time.Duration
 }
 
 const (
@@ -90,6 +91,7 @@ func (o *Options) addFlags() {
 	fs.StringVar(&o.AdditionalBinDir, "additional-bin-dir", "", "adds binDir option to configuration (used only with --multus-conf-file=auto)")
 	fs.BoolVar(&o.SkipTLSVerify, "skip-tls-verify", false, "skip TLS verify")
 	fs.BoolVar(&o.ForceCNIVersion, "force-cni-version", false, "force cni version to '--cni-version' (only for e2e-kind testing)")
+	fs.DurationVar(&o.WatchTimer, "multus-config-watch-timer", 1*time.Second, "how long to wait before reconciling multus config")
 	fs.MarkHidden("force-cni-version")
 	fs.MarkHidden("skip-tls-verify")
 }
@@ -594,9 +596,12 @@ func main() {
 		fmt.Printf("multus config file is created.\n")
 	}
 
+	watcher := time.NewTicker(opt.WatchTimer)
+	defer watcher.Stop()
+
 	if opt.CleanupConfigOnExit && opt.MultusConfFile == "auto" {
 		fmt.Printf("Entering watch loop...\n")
-		for {
+		for range watcher.C {
 			// Check kubeconfig and update if different (i.e. service account updated)
 			caHash, saTokenHash, err = opt.createKubeConfig(caHash, saTokenHash)
 			if err != nil {
@@ -625,7 +630,6 @@ func main() {
 				fmt.Fprintf(os.Stderr, "failed to create multus config: %v\n", err)
 				return
 			}
-			time.Sleep(1 * time.Second)
 		}
 	} else {
 		// sleep infinitely

docs/how-to-use.md

@@ -634,3 +634,7 @@ Sometimes, you may wish to not have the entrypoint copy the binary file onto the
 If you wish to have auto configuration use the `readinessindicatorfile` in the configuration, you can use the `--readiness-indicator-file` to express which file should be used as the readiness indicator.
 
     --readiness-indicator-file=/path/to/file
+
+The thin plugin will reconcile its kubeconfig and config file every second when using `--cleanup-config-on-exit` and `--multus-conf-file=auto`. The config poll interval is configurable with `--multus-config-watch-timer=<duration>`
+
+    --multus-config-watch-timer=5m