From: Amaury Denoyelle <adenoyelle@haproxy.com>
Date: Thu, 13 Nov 2025 16:45:18 +0000 (+0100)
Subject: MINOR: check: clarify check-reuse-pool interaction with reuse policy
X-Git-Tag: v3.3-dev13~24
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8415254cea9344bb4755092f32831e5b0e51a927;p=thirdparty%2Fhaproxy.git

MINOR: check: clarify check-reuse-pool interaction with reuse policy

check-reuse-pool can only perform as expected if reuse policy on the
backend is set to aggressive or higher. Update the documentation to
reflect this and implement a server diag warning.
---

diff --git a/doc/configuration.txt b/doc/configuration.txt
index 8987d9fec..c169ba9e7 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -17831,6 +17831,8 @@ check-reuse-pool
   completion. The main objective is to limit the number of connections opening
   and closure on a specific server. This feature is compatible only with
   http-check rulesets. It is silently ignored for other check types.
+  Furthermore, reuse policy should be set to aggressive on the backend as each
+  check attempt is performed over a dedicated session.
 
   For configuration simplicity, this option is silently ignored if any specific
   check connect option is defined, either on the server line or via a custom
diff --git a/include/haproxy/backend.h b/include/haproxy/backend.h
index 41ad4de6e..94ca8f8c5 100644
--- a/include/haproxy/backend.h
+++ b/include/haproxy/backend.h
@@ -46,6 +46,8 @@ int alloc_bind_address(struct sockaddr_storage **ss,
                        struct server *srv, struct proxy *be,
                        struct stream *s);
 
+int be_reuse_mode(const struct proxy *be, const struct server *srv);
+
 int64_t be_calculate_conn_hash(struct server *srv, struct stream *strm,
                                struct session *sess,
                                struct sockaddr_storage *src,
diff --git a/src/backend.c b/src/backend.c
index c1f0ab213..ae6eac255 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -1555,7 +1555,7 @@ kill_random_idle_conn(struct server *srv)
 /* Returns backend reuse policy depending on <be>. It can be forced to always
  * mode if <srv> is not NULL and uses reverse HTTP.
  */
-static int be_reuse_mode(struct proxy *be, struct server *srv)
+int be_reuse_mode(const struct proxy *be, const struct server *srv)
 {
 	if (srv && srv->flags & SRV_F_RHTTP) {
 		/* Override reuse-mode if reverse-connect is used. */
diff --git a/src/cfgdiag.c b/src/cfgdiag.c
index 80c277ac1..0d4e580d3 100644
--- a/src/cfgdiag.c
+++ b/src/cfgdiag.c
@@ -65,8 +65,8 @@ static void srv_diag_cookies(int *ret, struct server *srv, struct eb_root *cooki
 	}
 }
 
-/* Reports a diag if check-reuse-pool is active while backend check ruleset is
- * non HTTP.
+/* Reports a diag if check-reuse-pool is active but incompatible with the
+ * backend configuration.
  */
 static void srv_diag_check_reuse(int *ret, struct server *srv, struct proxy *px)
 {
@@ -75,6 +75,10 @@ static void srv_diag_check_reuse(int *ret, struct server *srv, struct proxy *px)
 			diag_warning(ret, "parsing [%s:%d] : 'server %s': check-reuse-pool is ineffective for non http-check rulesets.\n",
 			             srv->conf.file, srv->conf.line, srv->id);
 		}
+		else if (be_reuse_mode(px, srv) < PR_O_REUSE_AGGR) {
+			diag_warning(ret, "parsing [%s:%d] : 'server %s': check-reuse-pool is ineffective due to http-reuse policy.\n",
+			             srv->conf.file, srv->conf.line, srv->id);
+		}
 	}
 }