config: TCP clients hardlimit (default: 100)

The limit is global, threads are allowed equal portions of the limit.

doc/reference.rst

@@ -35,6 +35,7 @@ else.
       [ max-conn-idle ( integer | integer(s | m | h | d); ) ]
       [ max-conn-handshake ( integer | integer(s | m | h | d); ) ]
       [ max-conn-reply ( integer | integer(s | m | h | d); ) ]
+      [ max-tcp-clients integer; ]
       [ transfers integer; ]
       [ rate-limit integer; ]
       [ rate-limit-size integer; ]
@@ -227,6 +228,13 @@ max-conn-reply
 
 Maximum time to wait for a reply to an issued SOA query.
 
+.. _max-tcp-clients:
+
+max-tcp-clients
+^^^^^^^^^^^^^^^
+
+Maximum number of TCP clients connected in parallel, set this below file descriptor limit to avoid resource exhaustion.
+
 .. _transfers:
 
 transfers

man/knot.conf.5.in

@@ -83,6 +83,11 @@ system {
   # Default: 10s
   max-conn-reply 10s;
 
+  # Number of parallel TCP clients
+  # Set this below the descriptor limit to avoid resource exhaustion
+  # Default: 100
+  max-tcp-clients 100;
+
   # Number of parallel transfers
   # This number also includes pending SOA queries
   # Minimal value is number of CPUs

src/knot/conf/cf-lex.l

@@ -127,6 +127,7 @@ serial-policy   { lval.t = yytext; return SERIAL_POLICY; }
 max-conn-idle   { lval.t = yytext; return MAX_CONN_IDLE; }
 max-conn-handshake { lval.t = yytext; return MAX_CONN_HS; }
 max-conn-reply  { lval.t = yytext; return MAX_CONN_REPLY; }
+max-tcp-clients { lval.t = yytext; return MAX_TCP_CLIENTS; }
 rate-limit      { lval.t = yytext; return RATE_LIMIT; }
 rate-limit-size { lval.t = yytext; return RATE_LIMIT_SIZE; }
 rate-limit-slip { lval.t = yytext; return RATE_LIMIT_SLIP; }

src/knot/conf/cf-parse.y

@@ -518,6 +518,7 @@ static void ident_auto(void *scanner, int tok, conf_t *conf, bool val)
 %token <tok> MAX_CONN_IDLE
 %token <tok> MAX_CONN_HS
 %token <tok> MAX_CONN_REPLY
+%token <tok> MAX_TCP_CLIENTS
 %token <tok> RATE_LIMIT
 %token <tok> RATE_LIMIT_SIZE
 %token <tok> RATE_LIMIT_SLIP
@@ -659,6 +660,9 @@ system:
  | system MAX_CONN_REPLY INTERVAL ';' {
 	SET_INT(new_config->max_conn_reply, $3.i, "max-conn-reply");
  }
+ | system MAX_TCP_CLIENTS NUM ';' {
+	SET_INT(new_config->max_tcp_clients, $3.i, "max-tcp-clients");
+ }
  | system RATE_LIMIT NUM ';' {
 	SET_INT(new_config->rrl, $3.i, "rate-limit");
  }

src/knot/conf/conf.c

@@ -211,6 +211,9 @@ static int conf_process(conf_t *conf)
 	if (conf->max_conn_reply < 1) {
 		conf->max_conn_reply = CONFIG_REPLY_WD;
 	}
+	if (conf->max_tcp_clients < 1) {
+		conf->max_tcp_clients = CONFIG_MAXTCP;
+	}
 
 	/* Default interface. */
 	conf_iface_t *ctl_if = conf->ctl.iface;

src/knot/conf/conf.h

@@ -52,6 +52,7 @@
 #define CONFIG_REPLY_WD 10 /*!< SOA/NOTIFY query timeout [s]. */
 #define CONFIG_HANDSHAKE_WD 10 /*!< [secs] for connection to make a request.*/
 #define CONFIG_IDLE_WD  60 /*!< [secs] of allowed inactivity between requests */
+#define CONFIG_MAXTCP 100  /*!< Default limit on incoming TCP clients. */
 #define CONFIG_RRL_SLIP 1 /*!< Default slip value. */
 #define CONFIG_RRL_SIZE 393241 /*!< Htable default size. */
 #define CONFIG_XFERS 10
@@ -219,6 +220,7 @@ typedef struct conf_t {
 	int   max_conn_idle; /*!< TCP idle timeout. */
 	int   max_conn_hs;   /*!< TCP of inactivity before first query. */
 	int   max_conn_reply; /*!< TCP/UDP query timeout. */
+	int   max_tcp_clients; /*!< TCP client limit. */
 	int    rrl;      /*!< Rate limit (in responses per second). */
 	size_t rrl_size; /*!< Rate limit htable size. */
 	int    rrl_slip;  /*!< Rate limit SLIP. */