MEDIUM: sessions: Don't keep an infinite number of idling connections.

In session, don't keep an infinite number of connection that can idle.
Add a new frontend parameter, "max-session-srv-conns" to set a max number,
with a default value of 5.

doc/configuration.txt

@@ -5358,6 +5358,10 @@ max-keep-alive-queue <value>
   See also : "option http-server-close", "option prefer-last-server", server
              "maxconn" and cookie persistence.
 
+max-session-srv-conns <nb>
+  Set the maximum number of outgoing connections we can keep idling for a given
+  client session. The default is 5 (it precisely equals MAX_SRV_LIST which is
+  defined at build time).
 
 maxconn <conns>
   Fix the maximum number of concurrent connections on a frontend

include/proto/connection.h

@@ -664,7 +664,11 @@ static inline void conn_force_unsubscribe(struct connection *conn)
 static inline void conn_free(struct connection *conn)
 {
 	/* Remove ourself from the session's connections list, if any. */
-	LIST_DEL(&conn->session_list);
+	if (!LIST_ISEMPTY(&conn->session_list)) {
+		struct session *sess = conn->owner;
+		sess->resp_conns--;
+		LIST_DEL(&conn->session_list);
+	}
 	/* If we temporarily stored the connection as the stream_interface's
 	 * end point, remove it.
 	 */

include/proto/server.h

@@ -233,6 +233,27 @@ static inline enum srv_initaddr srv_get_next_initaddr(unsigned int *list)
 	return ret;
 }
 
+static inline int srv_add_to_idle_list(struct server *srv, struct connection *conn)
+{
+	if (srv && srv->pool_purge_delay > 0 && (srv->max_idle_conns == -1 ||
+	    srv->max_idle_conns > srv->curr_idle_conns) &&
+	    !(conn->flags & CO_FL_PRIVATE) &&
+	    ((srv->proxy->options & PR_O_REUSE_MASK) != PR_O_REUSE_NEVR) &&
+	    conn->mux->avail_streams(conn) == conn->mux->max_streams(conn)) {
+		LIST_DEL(&conn->list);
+		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])) &&
+		    !(task_in_rq(srv->idle_task[tid])))
+			task_schedule(srv->idle_task[tid],
+			    tick_add(now_ms, srv->pool_purge_delay));
+		return 1;
+	}
+	return 0;
+}
+
 #endif /* _PROTO_SERVER_H */
 
 /*

include/proto/session.h

@@ -30,7 +30,9 @@
 #include <types/global.h>
 #include <types/session.h>
 
+#include <proto/obj_type.h>
 #include <proto/stick_table.h>
+#include <proto/server.h>
 
 extern struct pool_head *pool_head_session;
 struct session *session_new(struct proxy *fe, struct listener *li, enum obj_type *origin);
@@ -76,6 +78,7 @@ static inline void session_add_conn(struct session *sess, struct connection *con
 	int avail = -1;
 	int i;
 
+	sess->resp_conns++;
 	for (i = 0; i < MAX_SRV_LIST; i++) {
 		if (sess->srv_list[i].target == target) {
 			avail = i;
@@ -99,6 +102,7 @@ static inline void session_add_conn(struct session *sess, struct connection *con
 		}
 		/* Now unown all the connections */
 		list_for_each_entry_safe(conn, conn_back, &sess->srv_list[avail].list, session_list) {
+			sess->resp_conns--;
 			conn->owner = NULL;
 			LIST_DEL(&conn->session_list);
 			LIST_INIT(&conn->session_list);
@@ -111,6 +115,24 @@ static inline void session_add_conn(struct session *sess, struct connection *con
 	LIST_ADDQ(&sess->srv_list[avail].list, &conn->session_list);
 }
 
+/* Returns 0 if the session can keep the idle conn, -1 if it was destroyed, or 1 if it was added to the server list */
+static inline int session_check_idle_conn(struct session *sess, struct connection *conn)
+{
+	if (sess->resp_conns > sess->fe->max_out_conns) {
+		/* We can't keep the connection, let's try to add it to the server idle list */
+		LIST_DEL(&conn->session_list);
+		LIST_INIT(&conn->session_list);
+		conn->owner = NULL;
+		sess->resp_conns--;
+		if (!srv_add_to_idle_list(objt_server(conn->target), conn)) {
+			/* The server doesn't want it, let's kill the connection right away */
+			conn->mux->destroy(conn);
+			return -1;
+		}
+		return 1;
+	}
+	return 0;
+}
 
 #endif /* _PROTO_SESSION_H */
 

include/types/proxy.h

@@ -278,6 +278,7 @@ struct proxy {
 
 	int options;				/* PR_O_REDISP, PR_O_TRANSP, ... */
 	int options2;				/* PR_O2_* */
+	int max_out_conns;                      /* Max number of idling connections we keep for a session */
 	struct in_addr mon_net, mon_mask;	/* don't forward connections from this net (network order) FIXME: should support IPv6 */
 	unsigned int ck_opts;			/* PR_CK_* (cookie options) */
 	unsigned int fe_req_ana, be_req_ana;	/* bitmap of common request protocol analysers for the frontend and backend */

include/types/session.h

@@ -54,6 +54,7 @@ struct session {
 	struct vars vars;               /* list of variables for the session scope. */
 	struct task *task;              /* handshake timeout processing */
 	long t_handshake;               /* handshake duration, -1 = not completed */
+	int resp_conns;                 /* Number of connections we're currently responsible for */
 	struct sess_srv_list srv_list[MAX_SRV_LIST]; /* List of servers and the connections the session is currently responsible for */
 };
 

src/backend.c

@@ -1254,8 +1254,9 @@ int connect_server(struct stream *s)
 				    (srv_conn->mux->avail_streams(srv_conn) == 1)) {
 					LIST_DEL(&old_conn->session_list);
 					LIST_INIT(&old_conn->session_list);
-					session_add_conn(sess, old_conn, s->target);
 					old_conn->owner = sess;
+					session_add_conn(sess, old_conn, s->target);
+					session_check_idle_conn(sess, old_conn);
 				}
 			}
 
@@ -1283,6 +1284,7 @@ int connect_server(struct stream *s)
 	if (srv_conn && old_conn != srv_conn) {
 		srv_conn->owner = s->sess;
 		LIST_DEL(&srv_conn->session_list);
+		LIST_INIT(&srv_conn->session_list);
 		session_add_conn(s->sess, srv_conn, s->target);
 	}
 

src/cfgparse-listen.c

@@ -421,6 +421,7 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 			curproxy->fe_sps_lim = defproxy.fe_sps_lim;
 
 			curproxy->to_log = defproxy.to_log & ~LW_COOKIE & ~LW_REQHDR & ~ LW_RSPHDR;
+			curproxy->max_out_conns = defproxy.max_out_conns;
 		}
 
 		if (curproxy->cap & PR_CAP_BE) {
@@ -1327,6 +1328,17 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 		else
 			curproxy->server_state_file_name = strdup(args[1]);
 	}
+	else if (!strcmp(args[0], "max-session-srv-conns")) {
+		if (warnifnotcap(curproxy, PR_CAP_FE, file, linenum, args[0], NULL))
+			err_code |= ERR_WARN;
+		if (*(args[1]) == 0) {
+			ha_alert("parsine [%s:%d] : '%s' expects a number. Got no argument\n",
+			    file, linenum, args[0]);
+			err_code |= ERR_ALERT | ERR_FATAL;
+			goto out;
+		}
+		curproxy->max_out_conns = atoi(args[1]);
+	}
 	else if (!strcmp(args[0], "capture")) {
 		if (warnifnotcap(curproxy, PR_CAP_FE, file, linenum, args[0], NULL))
 			err_code |= ERR_WARN;

src/cfgparse.c

@@ -455,6 +455,7 @@ void init_default_instance()
 	defproxy.redispatch_after = 0;
 	defproxy.lbprm.chash.balance_factor = 0;
 	defproxy.options = PR_O_REUSE_SAFE;
+	defproxy.max_out_conns = MAX_SRV_LIST;
 
 	defproxy.defsrv.check.inter = DEF_CHKINTR;
 	defproxy.defsrv.check.fastinter = 0;

src/mux_h1.c

@@ -1947,6 +1947,19 @@ static void h1_detach(struct conn_stream *cs)
 			h1c->conn->owner = sess;
 			session_add_conn(sess, h1c->conn, h1c->conn->target);
 		}
+		if (h1c->conn->owner == sess) {
+			int ret = session_check_idle_conn(sess, h1c->conn);
+			if (ret == -1)
+				/* The connection got destroyed, let's leave */
+				return;
+			else if (ret == 1) {
+				/* The connection was added to the server list,
+				 * wake the task so we can subscribe to events
+				 */
+				tasklet_wakeup(h1c->wait_event.task);
+				return;
+			}
+		}
 		/* we're in keep-alive with an idle connection, monitor it if not already done */
 		if (LIST_ISEMPTY(&h1c->conn->list)) {
 			struct server *srv = objt_server(h1c->conn->target);

src/mux_h2.c

@@ -2850,6 +2850,11 @@ static void h2_detach(struct conn_stream *cs)
 				h2c->conn->owner = sess;
 				session_add_conn(sess, h2c->conn, h2c->conn->target);
 			}
+			if (eb_is_empty(&h2c->streams_by_id)) {
+				if (session_check_idle_conn(h2c->conn->owner, h2c->conn) != 0)
+					/* At this point either the connection is destroyed, or it's been added to the server idle list, just stop */
+					return;
+			}
 			/* Never ever allow to reuse a connection from a non-reuse backend */
 			if ((h2c->proxy->options & PR_O_REUSE_MASK) == PR_O_REUSE_NEVR)
 				h2c->conn->flags |= CO_FL_PRIVATE;

src/proto_http.c

@@ -3489,9 +3489,19 @@ void http_end_txn_clean_session(struct stream *s)
 		srv_conn = NULL;
 	else if (!srv_conn->owner) {
 		srv_conn->owner = s->sess;
+		/* Add it unconditionally to the session list, it'll be removed
+		 * later if needed by session_check_idle_conn(), once we'll
+		 * have released the endpoint and know if it no longer has
+		 * attached streams, and so an idling connection
+		 */
 		session_add_conn(s->sess, srv_conn, s->target);
 	}
 	si_release_endpoint(&s->si[1]);
+	if (srv_conn && srv_conn->owner == s->sess) {
+		if (session_check_idle_conn(s->sess, srv_conn) != 0)
+			srv_conn = NULL;
+	}
+
 
 	s->si[1].state     = s->si[1].prev_state = SI_ST_INI;
 	s->si[1].err_type  = SI_ET_NONE;

src/session.c

@@ -64,6 +64,7 @@ struct session *session_new(struct proxy *fe, struct listener *li, enum obj_type
 			sess->srv_list[i].target = NULL;
 			LIST_INIT(&sess->srv_list[i].list);
 		}
+		sess->resp_conns = 0;
 	}
 	return sess;
 }
@@ -86,30 +87,11 @@ void session_free(struct session *sess)
 		list_for_each_entry_safe(conn, conn_back, &sess->srv_list[i].list, session_list) {
 			count++;
 			if (conn->mux) {
-				struct server *srv;
 
 				LIST_DEL(&conn->session_list);
 				LIST_INIT(&conn->session_list);
-				srv = objt_server(conn->target);
 				conn->owner = NULL;
-				if (srv && srv->pool_purge_delay > 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)) {
-					LIST_DEL(&conn->list);
-
-					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])) &&
-					    !(task_in_rq(srv->idle_task[tid])))
-						task_schedule(srv->idle_task[tid],
-						    tick_add(now_ms, srv->pool_purge_delay));
-				} else
+				if (!srv_add_to_idle_list(objt_server(conn->target), conn))
 					conn->mux->destroy(conn);
 			} else {
 				/* We have a connection, but not yet an associated mux.