From: Aurelien DARRAGON <adarragon@haproxy.com>
Date: Wed, 4 Oct 2023 15:30:02 +0000 (+0200)
Subject: MINOR: log/balance: support for the "random" lb algorithm
X-Git-Tag: v2.9-dev8~60
X-Git-Url: http://git.haproxy.org/?a=commitdiff_plain;h=e0b46600150ceb67d3051cc6ed1150708f0ae7a1;p=haproxy-3.0.git

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

In this patch we add basic support for the random algorithm:

random algorithm picks a random server using the result of the
statistical_prng() function as if it was a hash key to then compute the
related server ID.

There is no support for the <draw> parameter (which is implemented for
tcp/http load-balancing), because we don't have the required metrics to
evaluate server's load in log backends for the moment. Plus it would add
more complexity to the __do_send_log_backend() function so we'll keep it
this way for now but this might be needed in the future.
---

diff --git a/doc/configuration.txt b/doc/configuration.txt
index 6c903fc..d064357 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -8839,6 +8839,12 @@ log-balance <algorithm> [ <arguments> ]
                   goes back UP it is added at the end of the list so that the
                   sticky server doesn't change until it becomes DOWN.
 
+      random      A random number will be used as the key for the server
+                  lookup. Random log balancing can be useful with large farms
+                  or when servers are frequently added or removed from the
+                  pool of available servers as it may avoid the hammering
+                  effect that could result from roundrobin in this situation.
+
     <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 8b76a93..e0b5a58 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -2849,8 +2849,12 @@ int backend_parse_log_balance(const char **args, char **err, struct proxy *curpr
 		/* we use ALGO_FAS as "sticky" mode in log-balance context */
 		curproxy->lbprm.algo |= BE_LB_ALGO_FAS;
 	}
+	else if (strcmp(args[0], "random") == 0) {
+		curproxy->lbprm.algo &= ~BE_LB_ALGO;
+		curproxy->lbprm.algo |= BE_LB_ALGO_RND;
+	}
 	else {
-		memprintf(err, "only supports 'roundrobin', 'sticky' options");
+		memprintf(err, "only supports 'roundrobin', 'sticky', 'random', options");
 		return -1;
 	}
 	return 0;
diff --git a/src/log.c b/src/log.c
index 6900407..53011f7 100644
--- a/src/log.c
+++ b/src/log.c
@@ -2116,6 +2116,10 @@ static inline void __do_send_log_backend(struct proxy *be, struct log_header hdr
 		 */
 		targetid = 0;
 	}
+	else if ((be->lbprm.algo & BE_LB_ALGO) == BE_LB_ALGO_RND) {
+		/* random mode */
+		targetid = statistical_prng() % nb_srv;
+	}
 
  skip_lb: