Add logging for DNS update delays due to rate limit or backoff

packages/grpc-js/src/backoff-timeout.ts

@@ -78,6 +78,11 @@ export class BackoffTimeout {
    * running is true.
    */
   private startTime: Date = new Date();
+  /**
+   * The approximate time that the currently running timer will end. Only valid
+   * if running is true.
+   */
+  private endTime: Date = new Date();
 
   constructor(private callback: () => void, options?: BackoffOptions) {
     if (options) {
@@ -100,6 +105,8 @@ export class BackoffTimeout {
   }
 
   private runTimer(delay: number) {
+    this.endTime = this.startTime;
+    this.endTime.setMilliseconds(this.endTime.getMilliseconds() + this.nextDelay);
     clearTimeout(this.timerId);
     this.timerId = setTimeout(() => {
       this.callback();
@@ -178,4 +185,12 @@ export class BackoffTimeout {
     this.hasRef = false;
     this.timerId.unref?.();
   }
+
+  /**
+   * Get the approximate timestamp of when the timer will fire. Only valid if
+   * this.isRunning() is true.
+   */
+  getEndTime() {
+    return this.endTime;
+  }
 }

packages/grpc-js/src/resolver-dns.ts

@@ -353,6 +353,11 @@ class DnsResolver implements Resolver {
      * fires. Otherwise, start resolving immediately. */
     if (this.pendingLookupPromise === null) {
       if (this.isNextResolutionTimerRunning || this.backoff.isRunning()) {
+        if (this.isNextResolutionTimerRunning) {
+          trace('resolution update delayed by "min time between resolutions" rate limit');
+        } else {
+          trace('resolution update delayed by backoff timer until ' + this.backoff.getEndTime().toISOString());
+        }
         this.continueResolving = true;
       } else {
         this.startResolutionWithBackoff();

packages/grpc-js/src/resolving-load-balancer.ts

@@ -222,6 +222,7 @@ export class ResolvingLoadBalancer implements LoadBalancer {
          * In that case, the backoff timer callback will call
          * updateResolution */
         if (this.backoffTimeout.isRunning()) {
+          trace('requestReresolution delayed by backoff timer until ' + this.backoffTimeout.getEndTime().toISOString());
           this.continueResolving = true;
         } else {
           this.updateResolution();