MEDIUM: servers: Add a command to limit the number of idling connections.

Add a new command, "pool-max-conn" that sets the maximum number of connections
waiting in the orphan idling connections list (as activated with idle-timeout).
Using "-1" means unlimited. Using pools is now dependant on this.

doc/configuration.txt

@@ -11972,6 +11972,14 @@ on-marked-up <action>
 
   Actions are disabled by default
 
+pool-max-conn <max>
+  Set the maximum number of idling connections for a server. -1 means unlimited
+  connections, 0 means no idle connections. The default is -1. When idle
+  connections are enabled, orphaned idle connections which do not belong to any
+  client session anymore are moved to a dedicated pool so that they remain
+  usable by future clients. This only applies to connections that can be shared
+  according to the same principles as those applying to "http-reuse".
+
 port <port>
   Using the "port" parameter, it becomes possible to use a different port to
   send health-checks. On some servers, it may be desirable to dedicate a port

include/proto/connection.h

@@ -558,6 +558,7 @@ static inline void conn_init(struct connection *conn)
 	LIST_INIT(&conn->session_list);
 	conn->send_wait = NULL;
 	conn->recv_wait = NULL;
+	conn->idle_time = 0;
 }
 
 /* sets <owner> as the connection's owner */
@@ -673,6 +674,13 @@ static inline void conn_free(struct connection *conn)
 		if (objt_conn(s->si[1].end) == conn)
 			s->si[1].end = NULL;
 	}
+	/* The connection is currently in the server's idle list, so tell it
+	 * there's one less connection available in that list.
+	 */
+	if (conn->idle_time > 0) {
+		struct server *srv = __objt_server(conn->target);
+		srv->curr_idle_conns--;
+	}
 
 	conn_force_unsubscribe(conn);
 	LIST_DEL(&conn->list);

include/types/connection.h

@@ -446,7 +446,7 @@ struct connection {
 		struct sockaddr_storage from;	/* client address, or address to spoof when connecting to the server */
 		struct sockaddr_storage to;	/* address reached by the client, or address to connect to */
 	} addr; /* addresses of the remote side, client for producer and server for consumer */
-	unsigned int idle_time;                 /* Time the connection was added to the idle list */
+	unsigned int idle_time;                 /* Time the connection was added to the idle list, or 0 if not in the idle list */
 };
 
 /* PROTO token registration */

include/types/server.h

@@ -223,7 +223,9 @@ struct server {
 	struct list *safe_conns;		/* safe idle connections attached to stream interfaces, shared */
 	struct list *idle_orphan_conns;         /* Orphan connections idling */
 	unsigned int idle_timeout;              /* Time to keep an idling orphan connection alive */
-	struct task **idle_task;                 /* task responsible for cleaning idle orphan connections */
+	unsigned int max_idle_conns;            /* Max number of connection allowed in the orphan connections list */
+	unsigned int curr_idle_conns;           /* Current number of orphan idling connections */
+	struct task **idle_task;                /* task responsible for cleaning idle orphan connections */
 	struct task *warmup;                    /* the task dedicated to the warmup when slowstart is set */
 
 	struct conn_src conn_src;               /* connection source settings */

src/backend.c

@@ -1231,6 +1231,8 @@ int connect_server(struct stream *s)
 	 */
 	if (reuse && reuse_orphan) {
 		LIST_DEL(&srv_conn->list);
+		srv_conn->idle_time = 0;
+		srv->curr_idle_conns--;
 		LIST_ADDQ(&srv->idle_conns[tid], &srv_conn->list);
 		if (LIST_ISEMPTY(&srv->idle_orphan_conns[tid]))
 			task_unlink_wq(srv->idle_task[tid]);

src/cfgparse.c

@@ -471,6 +471,7 @@ void init_default_instance()
 	defproxy.defsrv.maxqueue = 0;
 	defproxy.defsrv.minconn = 0;
 	defproxy.defsrv.maxconn = 0;
+	defproxy.defsrv.max_idle_conns = -1;
 	defproxy.defsrv.slowstart = 0;
 	defproxy.defsrv.onerror = DEF_HANA_ONERR;
 	defproxy.defsrv.consecutive_errors_limit = DEF_HANA_ERRLIMIT;

src/server.c

@@ -380,6 +380,20 @@ static int srv_parse_idle_timeout(char **args, int *cur_arg, struct proxy *curpr
 	return 0;
 }
 
+static int srv_parse_pool_max_conn(char **args, int *cur_arg, struct proxy *curproxy, struct server *newsrv, char **err)
+{
+	char *arg;
+
+	arg = args[*cur_arg + 1];
+	if (!*arg) {
+		memprintf(err, "'%s' expects <value> as argument.\n", args[*cur_arg]);
+		return ERR_ALERT | ERR_FATAL;
+	}
+	newsrv->max_idle_conns = atoi(arg);
+
+	return 0;
+}
+
 /* parse the "id" server keyword */
 static int srv_parse_id(char **args, int *cur_arg, struct proxy *curproxy, struct server *newsrv, char **err)
 {
@@ -1230,6 +1244,7 @@ static struct srv_kw_list srv_kws = { "ALL", { }, {
 	{ "no-send-proxy-v2",    srv_parse_no_send_proxy_v2,    0,  1 }, /* Disable use of PROXY V2 protocol */
 	{ "non-stick",           srv_parse_non_stick,           0,  1 }, /* Disable stick-table persistence */
 	{ "observe",             srv_parse_observe,             1,  1 }, /* Enables health adjusting based on observing communication with the server */
+	{ "pool-max-conn",       srv_parse_pool_max_conn,       1,  1 }, /* Set the max number of orphan idle connections, 0 means unlimited */
 	{ "proto",               srv_parse_proto,               1,  1 }, /* Set the proto to use for all outgoing connections */
 	{ "proxy-v2-options",    srv_parse_proxy_v2_options,    1,  1 }, /* options for send-proxy-v2 */
 	{ "redir",               srv_parse_redir,               1,  1 }, /* Enable redirection mode */
@@ -1665,6 +1680,7 @@ static void srv_settings_cpy(struct server *srv, struct server *src, int srv_tmp
 #endif
 	srv->mux_proto = src->mux_proto;
 	srv->idle_timeout = src->idle_timeout;
+	srv->max_idle_conns = src->max_idle_conns;
 
 	if (srv_tmpl)
 		srv->srvrq = src->srvrq;
@@ -1708,6 +1724,9 @@ struct server *new_server(struct proxy *proxy)
 	srv->agent.server = srv;
 	srv->xprt  = srv->check.xprt = srv->agent.xprt = xprt_get(XPRT_RAW);
 
+	srv->idle_timeout = 1000;
+	srv->max_idle_conns = -1;
+
 	return srv;
 
   free_idle_conns:
@@ -1914,7 +1933,7 @@ static int server_finalize_init(const char *file, int linenum, char **args, int
 		px->srv_act++;
 	srv_lb_commit_status(srv);
 
-	if (!srv->tmpl_info.prefix && srv->idle_timeout != 0) {
+	if (!srv->tmpl_info.prefix && srv->max_idle_conns != 0) {
 			int i;
 
 			srv->idle_orphan_conns = calloc(global.nbthread, sizeof(*srv->idle_orphan_conns));
@@ -2019,7 +2038,7 @@ static int server_template_init(struct server *srv, struct proxy *px)
 		/* Linked backwards first. This will be restablished after parsing. */
 		newsrv->next = px->srv;
 		px->srv = newsrv;
-		if (newsrv->idle_timeout != 0) {
+		if (newsrv->max_idle_conns != 0) {
 			int i;
 
 			newsrv->idle_orphan_conns = calloc(global.nbthread, sizeof(*newsrv->idle_orphan_conns));

src/session.c

@@ -93,6 +93,8 @@ void session_free(struct session *sess)
 				srv = objt_server(conn->target);
 				conn->owner = NULL;
 				if (srv && srv->idle_timeout > 0 &&
+				    (srv->max_idle_conns == -1 ||
+				     srv->max_idle_conns > srv->curr_idle_conns) &&
 				    !(conn->flags & CO_FL_PRIVATE) &&
 				    conn->mux->avail_streams(conn) ==
 				    conn->mux->max_streams(conn)) {
@@ -100,6 +102,7 @@ void session_free(struct session *sess)
 
 					LIST_ADDQ(&srv->idle_orphan_conns[tid],
 					    &conn->list);
+					srv->curr_idle_conns++;
 
 					conn->idle_time = now_ms;
 					if (!(task_in_wq(srv->idle_task[tid])) &&