From: Aurelien DARRAGON <adarragon@haproxy.com>
Date: Thu, 21 Sep 2023 18:24:14 +0000 (+0200)
Subject: MINOR: log/balance: support for the "sticky" lb algorithm
X-Git-Tag: v2.9-dev8~61
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=26f73dbcbb7ed87157c532f08d3a4bccea526834;p=thirdparty%2Fhaproxy.git

MINOR: log/balance: support for the "sticky" lb algorithm

sticky algorithm always tries to send log messages to the first server in
the farm. The server will stay in front during queue and dequeue
operations (no other server can steal its place), unless it becomes
unavailable, in which case it will be replaced by another server from
the tree.
---

diff --git a/doc/configuration.txt b/doc/configuration.txt
index 584d604236..6c903fcd50 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -8833,6 +8833,12 @@ log-balance <algorithm> [ <arguments> ]
                   fairest algorithm when the server's processing time remains
                   equally distributed.
 
+      sticky      The first server in the list of available servers receives all
+                  the log messages. When the server goes DOWN, the next server
+                  in the list takes its place. When a previously DOWN server
+                  goes back UP it is added at the end of the list so that the
+                  sticky server doesn't change until it becomes DOWN.
+
     <arguments> is an optional list of arguments which may be needed by some
                 algorithms.
 
diff --git a/src/backend.c b/src/backend.c
index 190e95ee12..8b76a9343e 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -2844,8 +2844,13 @@ int backend_parse_log_balance(const char **args, char **err, struct proxy *curpr
 		curproxy->lbprm.algo &= ~BE_LB_ALGO;
 		curproxy->lbprm.algo |= BE_LB_ALGO_RR;
 	}
+	else if (strcmp(args[0], "sticky") == 0) {
+		curproxy->lbprm.algo &= ~BE_LB_ALGO;
+		/* we use ALGO_FAS as "sticky" mode in log-balance context */
+		curproxy->lbprm.algo |= BE_LB_ALGO_FAS;
+	}
 	else {
-		memprintf(err, "only supports 'roundrobin' option");
+		memprintf(err, "only supports 'roundrobin', 'sticky' options");
 		return -1;
 	}
 	return 0;
diff --git a/src/log.c b/src/log.c
index 7f01ddf93a..6900407a41 100644
--- a/src/log.c
+++ b/src/log.c
@@ -2109,6 +2109,13 @@ static inline void __do_send_log_backend(struct proxy *be, struct log_header hdr
 		 */
 		targetid = HA_ATOMIC_FETCH_ADD(&be->lbprm.log.lastid, 1) % nb_srv;
 	}
+	else if ((be->lbprm.algo & BE_LB_ALGO) == BE_LB_ALGO_FAS) {
+		/* sticky mode: use first server in the pool, which will always stay
+		 * first during dequeuing and requeuing, unless it becomes unavailable
+		 * and will be replaced by another one
+		 */
+		targetid = 0;
+	}
 
  skip_lb: