axfr: progressive bootstrap retry backoff backported

Conflicts:
	src/knot/server/xfr-handler.c

src/knot/server/xfr-handler.c

@@ -310,6 +310,7 @@ static int xfr_task_close(knot_ns_xfr_t *rq)
 	/* Reschedule failed bootstrap. */
 	if (rq->type == XFR_TYPE_AIN && !rq->zone->contents) {
 		/* Progressive retry interval up to AXFR_RETRY_MAXTIME */
+		zd->xfr_in.bootstrap_retry *= 2;
 		zone->xfr_in.bootstrap_retry += knot_random_uint32_t() % AXFR_BOOTSTRAP_RETRY;
 		if (zone->xfr_in.bootstrap_retry > AXFR_RETRY_MAXTIME) {
 			zone->xfr_in.bootstrap_retry = AXFR_RETRY_MAXTIME;

src/knot/server/zones.h

@@ -42,8 +42,8 @@
 
 /* Constants. */
 #define ZONES_JITTER_PCT    10 /*!< +-N% jitter to timers. */
-#define AXFR_BOOTSTRAP_RETRY (30*1000) /*!< Interval between AXFR BS retries. */
-#define AXFR_RETRY_MAXTIME (10*60*1000) /*!< Maximum interval 10mins */
+#define AXFR_BOOTSTRAP_RETRY (30*1000) /*!< Jitter cap between AXFR bootstrap retries. */
+#define AXFR_RETRY_MAXTIME (24*60*60*1000) /*!< Maximum AXFR retry interval cap of 24 hours. */
 
 /* Timer special values. */
 #define REFRESH_DEFAULT -1 /* Use time value from zone structure. */