MXS-2313: Add server ranks

The servers now accept a rank parameter that tells which servers to
prioritize.

include/maxscale/server.hh

@@ -28,6 +28,7 @@ extern const char CN_MONITORUSER[];
 extern const char CN_PERSISTMAXTIME[];
 extern const char CN_PERSISTPOOLMAX[];
 extern const char CN_PROXY_PROTOCOL[];
+extern const char CN_RANK[];
 
 /**
  * Status bits in the SERVER->status member, which describes the general state of a server. Although the
@@ -276,6 +277,13 @@ public:
      */
     virtual std::string protocol() const = 0;
 
+    /**
+     * Get server rank
+     *
+     * @return The server rank
+     */
+    virtual int rank() const = 0;
+
     /*
      * Update server address. TODO: Move this to internal class once blr is gone.
      *

server/core/config.cc

@@ -425,6 +425,7 @@ const MXS_MODULE_PARAM config_server_params[] =
     {CN_SSL_CERT_VERIFY_DEPTH,       MXS_MODULE_PARAM_COUNT,  "9"},
     {CN_SSL_VERIFY_PEER_CERTIFICATE, MXS_MODULE_PARAM_BOOL,   "true"},
     {CN_DISK_SPACE_THRESHOLD,        MXS_MODULE_PARAM_STRING},
+    {CN_RANK,                        MXS_MODULE_PARAM_INT,    "-1"},
     {NULL}
 };
 

server/core/config_runtime.cc

@@ -619,6 +619,13 @@ bool runtime_alter_server(Server* server, const char* key, const char* value)
             server->set_persistmaxtime(atoi(value));
         }
     }
+    if (strcmp(key, CN_RANK) == 0)
+    {
+        if (is_valid_integer(value))
+        {
+            server->set_rank(atoi(value));
+        }
+    }
     else
     {
         /**

server/core/internal/server.hh

@@ -62,6 +62,11 @@ public:
         m_settings.persistmaxtime = persistmaxtime;
     }
 
+    void set_rank(int rank)
+    {
+        m_settings.rank = rank;
+    }
+
     bool have_disk_space_limits() const override
     {
         std::lock_guard<std::mutex> guard(m_settings.lock);
@@ -117,6 +122,11 @@ public:
         return m_settings.authenticator;
     }
 
+    int rank() const override
+    {
+        return m_settings.rank;
+    }
+
     /**
      * Get a DCB from the persistent connection pool, if possible
      *
@@ -331,6 +341,8 @@ private:
         long persistpoolmax = 0;    /**< Maximum size of persistent connections pool */
         long persistmaxtime = 0;    /**< Maximum number of seconds connection can live */
 
+        int rank;   /*< The ranking of this server, used to prioritize certain servers over others */
+
         /** Disk space thresholds. Can be queried from modules at any time so access must be protected
          *  by mutex. */
         DiskSpaceLimits disk_space_limits;

server/core/server.cc

@@ -63,6 +63,7 @@ const char CN_MONITORUSER[] = "monitoruser";
 const char CN_PERSISTMAXTIME[] = "persistmaxtime";
 const char CN_PERSISTPOOLMAX[] = "persistpoolmax";
 const char CN_PROXY_PROTOCOL[] = "proxy_protocol";
+const char CN_RANK[] = "rank";
 
 namespace
 {
@@ -252,6 +253,11 @@ Server* Server::server_alloc(const char* name, MXS_CONFIG_PARAMETER* params)
     server->last_event = SERVER_UP_EVENT;
     server->status = SERVER_RUNNING;
 
+    if ((server->m_settings.rank = params->get_integer(CN_RANK)) == -1)
+    {
+        server->m_settings.rank = std::numeric_limits<int>::max();
+    }
+
     if (!monuser.empty())
     {
         mxb_assert(!monpw.empty());