From: Amaury Denoyelle <adenoyelle@haproxy.com>
Date: Fri, 6 Feb 2026 06:40:59 +0000 (+0100)
Subject: MINOR: backend: add function to check support for dynamic servers
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=817003aa310e918c64082655bf268edb399faf59;p=thirdparty%2Fhaproxy.git

MINOR: backend: add function to check support for dynamic servers

Move backend compatibility checks performed during 'add server' in a
dedicated function be_supports_dynamic_srv(). This should simplify
addition of future restriction.

This function will be reused when implementing backend creation at
runtime.
---

diff --git a/include/haproxy/backend.h b/include/haproxy/backend.h
index 120270730..6930ff256 100644
--- a/include/haproxy/backend.h
+++ b/include/haproxy/backend.h
@@ -69,6 +69,7 @@ int backend_parse_balance(const char **args, char **err, struct proxy *curproxy)
 int tcp_persist_rdp_cookie(struct stream *s, struct channel *req, int an_bit);
 
 int be_downtime(struct proxy *px);
+int be_supports_dynamic_srv(struct proxy *px, char **msg);
 void recount_servers(struct proxy *px);
 void update_backend_weight(struct proxy *px);
 
diff --git a/reg-tests/server/cli_add_server.vtc b/reg-tests/server/cli_add_server.vtc
index 8081312ba..93331a2bf 100644
--- a/reg-tests/server/cli_add_server.vtc
+++ b/reg-tests/server/cli_add_server.vtc
@@ -51,7 +51,7 @@ haproxy h1 -cli {
 
 	# invalid load-balancing algo
 	send "add server other/s1 ${s1_addr}:${s1_port}"
-	expect ~ "Backend must use a dynamic load balancing to support dynamic servers."
+	expect ~ "backend 'other' uses a non dynamic load balancing method"
 
 	# invalid mux proto
 	send "add server other2/s1 ${s1_addr}:${s1_port} proto h2"
diff --git a/src/backend.c b/src/backend.c
index 73b39306b..b531843fc 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -59,6 +59,7 @@
 #include <haproxy/task.h>
 #include <haproxy/ticks.h>
 #include <haproxy/time.h>
+#include <haproxy/tools.h>
 #include <haproxy/trace.h>
 
 #define TRACE_SOURCE &trace_strm
@@ -3055,6 +3056,27 @@ int be_downtime(struct proxy *px) {
 	return ns_to_sec(now_ns) - px->last_change + px->down_time;
 }
 
+/* Checks if <px> backend supports the addition of servers at runtime. Either a
+ * backend or a defaults proxy are supported. If proxy is incompatible, <msg>
+ * will be allocated to contain a textual explaination.
+ */
+int be_supports_dynamic_srv(struct proxy *px, char **msg)
+{
+	if (px->lbprm.algo && !(px->lbprm.algo & BE_LB_PROP_DYN)) {
+		memprintf(msg, "%s '%s' uses a non dynamic load balancing method",
+		          proxy_cap_str(px->cap), px->id);
+		return 0;
+	}
+
+	if (px->mode == PR_MODE_SYSLOG) {
+		memprintf(msg, "%s '%s' uses mode log",
+		          proxy_cap_str(px->cap), px->id);
+		return 0;
+	}
+
+	return 1;
+}
+
 /*
  * This function returns a string containing the balancing
  * mode of the proxy in a format suitable for stats.
diff --git a/src/server.c b/src/server.c
index d1bb43825..a475c881b 100644
--- a/src/server.c
+++ b/src/server.c
@@ -6104,7 +6104,7 @@ static int cli_parse_add_server(char **args, char *payload, struct appctx *appct
 	struct add_srv_ctx *ctx = applet_reserve_svcctx(appctx, sizeof(*ctx));
 	struct proxy *be;
 	struct server *srv;
-	char *be_name, *sv_name;
+	char *be_name, *sv_name, *errmsg;
 	int errcode, argc;
 	int next_id;
 	const int parse_flags = SRV_PARSE_DYNAMIC|SRV_PARSE_PARSE_ADDR;
@@ -6140,13 +6140,9 @@ static int cli_parse_add_server(char **args, char *payload, struct appctx *appct
 	if (!be)
 		return cli_err(appctx, "No such backend.\n");
 
-	if (!(be->lbprm.algo & BE_LB_PROP_DYN)) {
-		cli_err(appctx, "Backend must use a dynamic load balancing to support dynamic servers.\n");
-		return 1;
-	}
-
-	if (be->mode == PR_MODE_SYSLOG) {
-		cli_err(appctx," Dynamic servers cannot be used with log backends.\n");
+	errmsg = NULL;
+	if (!be_supports_dynamic_srv(be, &errmsg)) {
+		cli_dynerr(appctx, memprintf(&errmsg, "Backend does not support dynamic servers : %s.\n", errmsg));
 		return 1;
 	}