Use cluster connections too, to limit maxclients.

See #7401.

src/cluster.c

@@ -691,6 +691,13 @@ void clusterAcceptHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
     }
 }
 
+/* Return the approximated number of sockets we are using in order to
+ * take the cluster bus connections. */
+unsigned long getClusterConnectionsCount(void) {
+    return server.cluster_enabled ?
+           (dictSize(server.cluster->nodes)*2) : 0;
+}
+
 /* -----------------------------------------------------------------------------
  * Key space handling
  * -------------------------------------------------------------------------- */

src/cluster.h

@@ -283,5 +283,6 @@ typedef struct {
 clusterNode *getNodeByQuery(client *c, struct redisCommand *cmd, robj **argv, int argc, int *hashslot, int *ask);
 int clusterRedirectBlockedClientIfNeeded(client *c);
 void clusterRedirectClient(client *c, clusterNode *n, int hashslot, int error_code);
+unsigned long getClusterConnectionsCount(void);
 
 #endif /* __CLUSTER_H */

src/networking.c

@@ -892,17 +892,24 @@ static void acceptCommonHandler(connection *conn, int flags, char *ip) {
     client *c;
     UNUSED(ip);
 
-    /* Admission control will happen before a client is created and connAccept()
+    /* Limit the number of connections we take at the same time.
+     *
+     * Admission control will happen before a client is created and connAccept()
      * called, because we don't want to even start transport-level negotiation
-     * if rejected.
-     */
-    if (listLength(server.clients) >= server.maxclients) {
-        char *err = "-ERR max number of clients reached\r\n";
+     * if rejected. */
+    if (listLength(server.clients) + getClusterConnectionsCount()
+        >= server.maxclients)
+    {
+        char *err;
+        if (server.cluster_enabled)
+            err = "-ERR max number of clients reached\r\n";
+        else
+            err = "-ERR max number of clients + cluster "
+                  "connections reached\r\n";
 
         /* That's a best effort error message, don't check write errors.
-         * Note that for TLS connections, no handshake was done yet so nothing is written
-         * and the connection will just drop.
-         */
+         * Note that for TLS connections, no handshake was done yet so nothing
+         * is written and the connection will just drop. */
         if (connWrite(conn,err,strlen(err)) == -1) {
             /* Nothing to do, Just to avoid the warning... */
         }