MINOR: Add ability for agent-check to set server maxconn

This is very useful in complex architecture systems where HAproxy
is balancing DB connections for example. We want to keep the maxconn
high in order to avoid issues with queueing on the LB level when
there is slowness on another part of the system. Example is a case of
an architecture where each thread opens multiple DB connections, which
if get stuck in queue cause a snowball effect (old connections aren't
closed, new ones cannot be established). These connections are mostly
idle and the DB server has no problem handling thousands of them.

Allowing us to dynamically set maxconn depending on the backend usage
(LA, CPU, memory, etc.) enables us to have high maxconn for situations
like above, but lowering it in case there are real issues where the
backend servers become overloaded (cache issues, DB gets hit hard).

diff --git a/doc/configuration.txt b/doc/configuration.txt
index 5a815a175caa47dca1fb59fd776cd89bae8536ff..5345b33023d85dc49b9428b33db99135389087e0 100644 (file)
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -10184,6 +10184,12 @@ agent-check
     weight is reported on the stats page as "DRAIN" since it has the same
     effect on the server (it's removed from the LB farm).
 
+  - The string "maxconn:" followed by an integer (no space between). Values in
+    this format will set the maxconn of a server. The maximum number of
+    connections advertised needs to be multipled by the number of load balancers
+    and different backends that use this health check to get the total number
+    of connections the server might receive. Example: maxconn:30
+
   - The word "ready". This will turn the server's administrative state to the
     READY mode, thus cancelling any DRAIN or MAINT state
 

diff --git a/include/proto/server.h b/include/proto/server.h
index 872503c1a7f0ca094df655df02b774b2429b0bab..ee45f63c0f4283bcd4c4799b34cff4d65ef6ef75 100644 (file)
--- a/include/proto/server.h
+++ b/include/proto/server.h
@@ -112,6 +112,13 @@ const char *server_parse_weight_change_request(struct server *sv,
 const char *server_parse_addr_change_request(struct server *sv,
                                              const char *addr_str, const char *updater);
 
+/*
+ * Parses maxconn_str and configures sv accordingly.
+ * Returns NULL on success, error message string otherwise.
+ */
+const char *server_parse_maxconn_change_request(struct server *sv,
+                                              const char *maxconn_str);
+
 /*
  * Return true if the server has a zero user-weight, meaning it's in draining
  * mode (ie: not taking new non-persistent connections).

diff --git a/src/checks.c b/src/checks.c
index 35fd020e3e2c55fe7e3b61114ed7cf4915861a9c..c4ac947b60514b3f0b78e9c17b4524200d926141 100644 (file)
--- a/src/checks.c
+++ b/src/checks.c
@@ -938,6 +938,7 @@ static void event_srv_chk_r(struct connection *conn)
                const char *hs = NULL; /* health status      */
                const char *as = NULL; /* admin status */
                const char *ps = NULL; /* performance status */
+               const char *cs = NULL; /* maxconn */
                const char *err = NULL; /* first error to report */
                const char *wrn = NULL; /* first warning to report */
                char *cmd, *p;
@@ -1039,10 +1040,14 @@ static void event_srv_chk_r(struct connection *conn)
                        else if (strcasecmp(cmd, "maint") == 0) {
                                as = cmd;
                        }
-                       /* else try to parse a weight here and keep the last one */
+                       /* try to parse a weight here and keep the last one */
                        else if (isdigit((unsigned char)*cmd) && strchr(cmd, '%') != NULL) {
                                ps = cmd;
                        }
+                       /* try to parse a maxconn here */
+                       else if (strncasecmp(cmd, "maxconn:", strlen("maxconn:")) == 0) {
+                               cs = cmd;
+                       }
                        else {
                                /* keep a copy of the first error */
                                if (!err)
@@ -1079,6 +1084,16 @@ static void event_srv_chk_r(struct connection *conn)
                                wrn = msg;
                }
 
+               if (cs) {
+                       const char *msg;
+
+                       cs += strlen("maxconn:");
+
+                       msg = server_parse_maxconn_change_request(s, cs);
+                       if (!wrn || !*wrn)
+                               wrn = msg;
+               }
+
                /* and finally health status */
                if (hs) {
                        /* We'll report some of the warnings and errors we have

diff --git a/src/server.c b/src/server.c
index 5a2c58a8f2d410605b5a4ba11deb7cab4bc749c3..10957548e84b0120dac88fd0e5bcaaf0109e8cdf 100644 (file)
--- a/src/server.c
+++ b/src/server.c
@@ -831,6 +831,33 @@ const char *server_parse_addr_change_request(struct server *sv,
        return "Could not understand IP address format.\n";
 }
 
+const char *server_parse_maxconn_change_request(struct server *sv,
+                                                const char *maxconn_str)
+{
+       long int v;
+       char *end;
+
+       if (!*maxconn_str)
+               return "Require <maxconn>.\n";
+
+       v = strtol(maxconn_str, &end, 10);
+       if (end == maxconn_str)
+               return "maxconn string empty or preceded by garbage";
+       else if (end[0] != '\0')
+               return "Trailing garbage in maxconn string";
+
+       if (sv->maxconn == sv->minconn) { // static maxconn
+               sv->maxconn = sv->minconn = v;
+       } else { // dynamic maxconn
+               sv->maxconn = v;
+       }
+
+       if (may_dequeue_tasks(sv, sv->proxy))
+               process_srv_queue(sv);
+
+       return NULL;
+}
+
 int parse_server(const char *file, int linenum, char **args, struct proxy *curproxy, struct proxy *defproxy)
 {
        struct server *newsrv = NULL;