From: Christopher Faulet <cfaulet@haproxy.com>
Date: Wed, 2 May 2018 10:12:45 +0000 (+0200)
Subject: BUG/MINOR: checks: Fix check->health computation for flapping servers
X-Git-Tag: v1.9-dev1~278
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b119a79fc336f2b6074de1c3113b1682c717985c;p=thirdparty%2Fhaproxy.git

BUG/MINOR: checks: Fix check->health computation for flapping servers

This patch fixes an old bug introduced in the commit 7b1d47ce ("MAJOR: checks:
move health checks changes to set_server_check_status()"). When a DOWN server is
flapping, everytime a check succeds, check->health is incremented. But when a
check fails, it is decremented only when it is higher than the rise value. So if
only one check succeds for a DOWN server, check->health will remain set to 1 for
all subsequent failing checks.

So, at first glance, it seems not that terrible because the server remains
DOWN. But it is reported in the transitional state "DOWN server, going up". And
it will remain in this state until it is UP again. And there is also an
insidious side effect. If a DOWN server is flapping time to time, It will end to
be considered UP after a uniq successful check, , regardless the rise threshold,
because check->health will be increased slowly and never decreased.

To fix the bug, we just need to reset check->health to 0 when a check fails for
a DOWN server. To do so, we just need to relax the condition to handle a failure
in the function set_server_check_status.

This patch must be backported to haproxy 1.5 and newer.
---

diff --git a/src/checks.c b/src/checks.c
index 80a9c70d2a..d07a82f84b 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -243,7 +243,7 @@ static void set_server_check_status(struct check *check, short status, const cha
 		 */
 		if ((!(check->state & CHK_ST_AGENT) ||
 		    (check->status >= HCHK_STATUS_L57DATA)) &&
-		    (check->health >= check->rise)) {
+		    (check->health > 0)) {
 			HA_ATOMIC_ADD(&s->counters.failed_checks, 1);
 			report = 1;
 			check->health--;