From 5ce08521d57f72606d9e0b7bdc1ad227bf56b478 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Thu, 11 Aug 2022 21:38:36 -0700
Subject: [PATCH] ircd::net::dns: Perturb the minimum TTL to avoid groupings on
 expiration.

---
 ircd/net_dns.cc | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/ircd/net_dns.cc b/ircd/net_dns.cc
index a13992d73..35b1fdd6b 100644
--- a/ircd/net_dns.cc
+++ b/ircd/net_dns.cc
@@ -239,24 +239,29 @@ bool
 ircd::net::dns::expired(const json::object &rr,
                         const time_t &rr_ts)
 {
-	const seconds &min_seconds
-	{
-		cache::min_ttl
-	};
-
-	const seconds &err_seconds
-	{
-		cache::error_ttl
-	};
-
-	const time_t &min
+	const seconds base
 	{
 		is_error(rr)?
-			err_seconds.count():
-			min_seconds.count()
+			seconds(cache::error_ttl):
+			seconds(cache::min_ttl)
 	};
 
-	return expired(rr, rr_ts, min);
+	const pair<u64> perturb_range
+	{
+		1, base.count() / 3
+	};
+
+	const seconds perturb
+	{
+		rand::integer(perturb_range.first, perturb_range.second)
+	};
+
+	const seconds min
+	{
+		base + perturb
+	};
+
+	return expired(rr, rr_ts, min.count());
 }
 
 bool