Set server name implementation

doc/configuration.txt

@@ -5943,6 +5943,7 @@ option pgsql-check                        X          -         X         X
 option prefer-last-server            (*)  X          -         X         X
 option redispatch                    (*)  X          -         X         X
 option redis-check                        X          -         X         X
+option server-rename                      -          -         X         X
 option smtpchk                            X          -         X         X
 option socket-stats                  (*)  X          X         X         -
 option splice-auto                   (*)  X          X         X         X
@@ -6031,6 +6032,35 @@ use-server                                -          -         X         X
 
 
 4.2. Alphabetically sorted keywords reference
+
+option server-rename
+  Enable runtime renaming of servers via the CLI.
+
+  May be used in the following contexts: tcp, http
+
+  May be used in sections :   defaults | frontend | listen | backend
+                                 no    |    no    |   no   |   yes
+
+  When this option is enabled in a backend, it allows the name of any server in that backend to be changed at runtime using the CLI command:
+      set server <backend>/<server> name <newname>
+
+  Restrictions:
+    - The new name must be unique among all servers in the backend.
+    - The change is effective immediately for all runtime operations, stats, and logs.
+    - The new name is not persisted to the configuration file and will be lost on reload.
+    - Renaming is only available if 'option server-rename' is set in the backend.
+    - Some features that rely on static server names (such as certain stick-tables or external monitoring) may not recognize the new name until restart.
+
+  Example:
+      backend myapp
+        option server-rename
+        server s1 10.0.0.1:80
+        server s2 10.0.0.2:80
+
+  To rename server 's1' to 'blue':
+      echo "set server myapp/s1 name blue" | socat /var/run/haproxy.sock -
+
+  See also: 'set server <b>/<s> name' in the management guide (doc/management.txt).
 ---------------------------------------------
 
 This section provides a description of each keyword and its usage.

doc/management.txt

@@ -2663,6 +2663,36 @@ set server <backend>/<server> ssl [ on | off ]  (deprecated)
   This command is deprecated, create a new server dynamically with or without
   SSL instead, using the "add server" command.
 
+set server <backend>/<server> name <newname>
+  Change the name of a server at runtime (if 'option server-rename'
+  is enabled in the backend).
+
+  The new name must be unique among all servers in the backend. The
+  change is effective immediately for all runtime operations, stats,
+  and logs, but is not persisted to the configuration file and will
+  be lost on reload. Some features that rely on static server names
+  (such as stick-tables or external monitoring) may not recognize
+  the new name until restart.
+
+  There is no strict requirement that no sessions are active
+  before renaming. However, if there are active sessions, log entries
+  for those sessions may use either the old or new name, depending on
+  when the rename occurs relative to logging. This may result in split
+  or inconsistent logs for in-flight requests. If strict log consistency
+  is required, it is the user's responsibility to ensure all sessions
+  have finished before renaming (e.g., by draining or maintenance mode
+  and waiting for all connections to close).
+
+  For most use cases, a clear naming scheme (such as srv1 → srv1-old,
+  srv1-new, or srv1*) allows correlating log entries before and after
+  the rename, even if some overlap occurs. Users should choose a naming
+  convention that fits their operational and troubleshooting needs.
+
+  Example:
+      set server myapp/s1 name blue
+
+  See also: 'option server-rename' in doc/configuration.txt.
+
 set severity-output [ none | number | string ]
   Change the severity output format of the stats socket connected to for the
   duration of the current session.

include/haproxy/event_hdl-t.h

@@ -279,6 +279,8 @@ struct event_hdl_sub {
 #define EVENT_HDL_SUB_SERVER_CHECK                      EVENT_HDL_SUB_TYPE(1,7)
 /* server inet addr (addr:svc_port tuple) change event */
 #define EVENT_HDL_SUB_SERVER_INETADDR                   EVENT_HDL_SUB_TYPE(1,8)
+/* server name change event */
+#define EVENT_HDL_SUB_SERVER_NAME                       EVENT_HDL_SUB_TYPE(1,9)
 
 /* PAT_REF family, only published in pat ref subscription list
  * (not published in global subscription list for performance reasons)

include/haproxy/proxy-t.h

@@ -187,7 +187,9 @@ enum PR_SRV_STATE_FILE {
 #define PR_O3_HASHAFNTY_MAXQUEUE 0x00000200 /* preserve hash affinity until maxqueue is reached */
 #define PR_O3_HASHAFNTY_MASK     0x00000300 /* mask for hash-preserve-affinity */
 
-/* unused: 0x00000400 to  0x80000000 */
+#define PR_O3_SRV_RENAME         0x00000400 /* allow runtime server renaming */
+
+/* unused: 0x00000800 to  0x80000000 */
 /* end of proxy->options3 */
 
 /* Cookie settings for pr->ck_opts */

include/haproxy/server-t.h

@@ -565,6 +565,7 @@ struct event_hdl_cb_data_server {
 	 *   EVENT_HDL_SUB_SERVER_ADMIN
 	 *   EVENT_HDL_SUB_SERVER_CHECK
 	 *   EVENT_HDL_SUB_SERVER_INETADDR
+	 *   EVENT_HDL_SUB_SERVER_NAME
 	 */
 	struct {
 		/* safe data can be safely used from both
@@ -768,6 +769,24 @@ struct event_hdl_cb_data_server_inetaddr {
 	/* no unsafe data */
 };
 
+/* data provided to EVENT_HDL_SUB_SERVER_NAME handlers through
+ * event_hdl facility
+ *
+ * Note that this may be casted to regular event_hdl_cb_data_server if
+ * you don't care about name related optional info
+ */
+struct event_hdl_cb_data_server_name {
+	/* provided by:
+	 *   EVENT_HDL_SUB_SERVER_NAME
+	 */
+	struct event_hdl_cb_data_server server;                 /* must be at the beginning */
+	struct {
+		char old_name[64];
+		char new_name[64];
+	} safe;
+	/* no unsafe data */
+};
+
 /* Storage structure to load server-state lines from a flat file into
  * an ebtree, for faster processing
  */

src/proxy.c

@@ -156,6 +156,7 @@ const struct cfg_opt cfg_opts3[] =
 {
 	{"assume-rfc6587-ntf",            PR_O3_ASSUME_RFC6587_NTF, PR_CAP_FE, 0, PR_MODE_SYSLOG },
 	{"dont-parse-log",                PR_O3_DONTPARSELOG, PR_CAP_FE, 0, PR_MODE_SYSLOG },
+	{"server-rename",                 PR_O3_SRV_RENAME, PR_CAP_BE, 0, 0 },
 	{ NULL, 0, 0, 0 }
 };
 

src/server.c

@@ -56,6 +56,8 @@
 #include <haproxy/tools.h>
 #include <haproxy/xxhash.h>
 #include <haproxy/event_hdl.h>
+#include <haproxy/stick_table-t.h>
+#include <haproxy/peers-t.h>
 
 static void srv_update_status(struct server *s, int type, int cause);
 static int srv_apply_lastaddr(struct server *srv, int *err_code);
@@ -5397,6 +5399,114 @@ const char *srv_update_fqdn(struct server *server, const char *fqdn, const char
 }
 
 
+/* Rename a server at runtime. This function handles all precondition checks,
+ * tree re-indexing under thread_isolate(), and event publication.
+ *
+ * The caller must NOT hold any lock — this function uses thread_isolate()
+ * internally for tree manipulation.
+ *
+ * Preconditions enforced:
+ *   - backend must have "option server-rename" set
+ *   - server must be administratively in maintenance
+ *   - new name must not conflict with an existing server in the backend
+ *   - new name must be syntactically valid (no spaces, '/', '#' prefix)
+ *   - backend must not have sticking rules referencing a peer-synced table
+ *
+ * Returns NULL on success, or a pointer to a static/trash error message
+ * string on failure. On success, a ha_notice() is emitted and the
+ * EVENT_HDL_SUB_SERVER_NAME event is published.
+ */
+static const char *srv_update_server_name(struct server *srv, const char *new_name)
+{
+	struct proxy *be = srv->proxy;
+	struct sticking_rule *rule;
+	char *old_name;
+	char *dup;
+	const char *p;
+
+	/* validate the new name is not empty */
+	if (!*new_name)
+		return "Require a new server name.\n";
+
+	/* reject names starting with '#' (numeric ID syntax in server_find) */
+	if (*new_name == '#')
+		return "Server name must not start with '#'.\n";
+
+	/* reject control characters, spaces, and '/' which break CLI parsing */
+	for (p = new_name; *p; p++) {
+		if ((unsigned char)*p <= ' ' || *p == '/')
+			return "Server name must not contain spaces, control characters, or '/'.\n";
+	}
+
+	/* per-backend opt-in required */
+	if (!(be->options3 & PR_O3_SRV_RENAME))
+		return "Backend does not allow server renaming (add 'option server-rename').\n";
+
+	/* server must be administratively down (in maintenance) */
+	if (!(srv->cur_admin & SRV_ADMF_MAINT))
+		return "Server must be in maintenance mode to be renamed (set server <b>/<s> state maint).\n";
+
+	/* reject if any sticking rule references a peer-synced table */
+	list_for_each_entry(rule, &be->sticking_rules, list) {
+		if (rule->table.t && rule->table.t->peers.p)
+			return "Cannot rename: backend has sticking rules using a peer-synced table.\n";
+	}
+	list_for_each_entry(rule, &be->storersp_rules, list) {
+		if (rule->table.t && rule->table.t->peers.p)
+			return "Cannot rename: backend has store-response rules using a peer-synced table.\n";
+	}
+
+	/* same name is a no-op success */
+	if (strcmp(srv->id, new_name) == 0)
+		return NULL;
+
+	/* allocate new name before taking isolation */
+	dup = strdup(new_name);
+	if (!dup)
+		return "Out of memory allocating new server name.\n";
+
+	/* tree manipulation requires thread isolation (same pattern as
+	 * add/del server). This is rare enough that the cost is acceptable.
+	 */
+	thread_isolate();
+
+	/* re-check for name conflict under isolation — another rename or
+	 * add server could have raced before we isolated.
+	 */
+	if (server_find_by_name(be, new_name)) {
+		thread_release();
+		free(dup);
+		return "A server with the same name already exists in this backend.\n";
+	}
+
+	/* --- point of no return --- */
+
+	old_name = srv->id;
+
+	/* re-index in the name tree */
+	cebis_item_delete(&be->conf.used_server_name, conf.name_node, id, srv);
+	srv->id = dup;
+	cebis_item_insert(&be->conf.used_server_name, conf.name_node, id, srv);
+
+	/* publish rename event with both old and new names */
+	{
+		struct event_hdl_cb_data_server_name cb_data;
+
+		_srv_event_hdl_prepare(&cb_data.server, srv, 1);
+		snprintf(cb_data.safe.old_name, sizeof(cb_data.safe.old_name), "%s", old_name);
+		snprintf(cb_data.safe.new_name, sizeof(cb_data.safe.new_name), "%s", new_name);
+		_srv_event_hdl_publish(EVENT_HDL_SUB_SERVER_NAME, cb_data, srv);
+	}
+
+	thread_release();
+
+	ha_notice("Server %s/%s renamed from '%s'.\n", be->id, srv->id, old_name);
+	free(old_name);
+
+	return NULL;
+}
+
+
 /* Expects to find a backend and a server in <arg> under the form <backend>/<server>,
  * and returns the pointer to the server. Otherwise, display adequate error messages
  * on the CLI, sets the CLI's state to CLI_ST_PRINT and returns NULL. This is only
@@ -5654,11 +5764,26 @@ static int cli_parse_set_server(char **args, char *payload, struct appctx *appct
 #else
 		cli_msg(appctx, LOG_NOTICE, "server ssl setting not supported.\n");
 #endif
-	} else {
+	}
+	else if (strcmp(args[3], "name") == 0) {
+		if (!*args[4]) {
+			cli_err(appctx, "set server <b>/<s> name requires a new name.\n");
+			goto out;
+		}
+		/* srv_update_server_name() handles its own locking via
+		 * thread_isolate(), so do NOT hold the server lock here.
+		 */
+		warning = srv_update_server_name(sv, args[4]);
+		if (warning)
+			cli_err(appctx, warning);
+		else
+			cli_msg(appctx, LOG_NOTICE, "Server name updated.\n");
+	}
+	else {
 		cli_err(appctx,
 			"usage: set server <backend>/<server> "
 			"addr | agent | agent-addr | agent-port | agent-send | "
-			"check-addr | check-port | fqdn | health | ssl | "
+			"check-addr | check-port | fqdn | health | name | ssl | "
 			"state | weight\n");
 	}
  out:
@@ -6533,7 +6658,7 @@ static struct cli_kw_list cli_kws = {{ },{
 	{ { "enable", "health",  NULL },         "enable health                           : enable health checks",                                        cli_parse_enable_health, NULL },
 	{ { "enable", "server",  NULL },         "enable server  (DEPRECATED)             : enable a disabled server (use 'set server' instead)",         cli_parse_enable_server, NULL },
 	{ { "set", "maxconn", "server",  NULL }, "set maxconn server <bk>/<srv>           : change a server's maxconn setting",                           cli_parse_set_maxconn_server, NULL },
-	{ { "set", "server", NULL },             "set server <bk>/<srv> [opts]            : change a server's state, weight, address or ssl",             cli_parse_set_server },
+	{ { "set", "server", NULL },             "set server <bk>/<srv> [opts]            : change a server's state, weight, address, name or ssl",  cli_parse_set_server },
 	{ { "get", "weight", NULL },             "get weight <bk>/<srv>                   : report a server's current weight",                            cli_parse_get_weight },
 	{ { "set", "weight", NULL },             "set weight <bk>/<srv>  (DEPRECATED)     : change a server's weight (use 'set server' instead)",         cli_parse_set_weight },
 	{ { "add", "server", NULL },             "add server <bk>/<srv>                   : create a new server",                                         cli_parse_add_server, cli_io_handler_add_server },