Progressive bootstrap interval up to 10mins.

src/knot/server/xfr-handler.c

@@ -321,14 +321,17 @@ static int xfr_task_close(knot_ns_xfr_t *rq)
 
 	/* Reschedule failed bootstrap. */
 	if (rq->type == XFR_TYPE_AIN && !knot_zone_contents(rq->zone)) {
-		int tmr_s = AXFR_BOOTSTRAP_RETRY * tls_rand();
+		/* Progressive retry interval up to AXFR_RETRY_MAXTIME */
+		zd->xfr_in.bootstrap_retry += AXFR_BOOTSTRAP_RETRY * tls_rand();
+		if (zd->xfr_in.bootstrap_retry > AXFR_RETRY_MAXTIME)
+			zd->xfr_in.bootstrap_retry = AXFR_RETRY_MAXTIME;
 		event_t *ev = zd->xfr_in.timer;
 		if (ev) {
 			evsched_cancel(ev->parent, ev);
-			evsched_schedule(ev->parent, ev, tmr_s);
+			evsched_schedule(ev->parent, ev, zd->xfr_in.bootstrap_retry);
 		}
 		log_zone_notice("%s Bootstrap failed, next attempt in %d seconds.\n",
-		                rq->msg, tmr_s / 1000);
+		                rq->msg, zd->xfr_in.bootstrap_retry / 1000);
 	}
 
 	/* Close socket and free task. */

src/knot/server/zones.h

@@ -45,6 +45,7 @@
 #define ZONES_JITTER_PCT    10 /*!< +-N% jitter to timers. */
 #define IXFR_DBSYNC_TIMEOUT (60*1000) /*!< Database sync timeout = 60s. */
 #define AXFR_BOOTSTRAP_RETRY (30*1000) /*!< Interval between AXFR BS retries. */
+#define AXFR_RETRY_MAXTIME (10*60*1000) /*!< Maximum interval 10mins */
 
 enum {
 	REFRESH_DEFAULT = -1 /* Use time value from zone structure. */