Add monitor parameter to services

Services now accept a monitor as a source for servers. This removes the
need to redundantly list the same servers parameters in multiple places.

Documentation/Getting-Started/Configuration-Guide.md

@@ -589,6 +589,42 @@ filters=counter | QLA
 The requests pass through the filters from left to right in the order defined in
 the configuration parameter.
 
+#### `monitor`
+
+The monitor parameter tells the service which cluster of servers to use. The
+value of the option is the name of a monitor object. This removes the redundant
+definition of servers in both services and monitors.
+
+If both the `monitor` and `servers` parameters are defined, only the `monitor`
+parameter will be used.
+
+Only one cluster can be defined for a service. Multi-cluster setups should use
+the `servers` parameter to list the servers that the service should use.
+
+Here is an excerpt from an example configuration with a service that defines the
+cluster parameter.
+
+```
+[db-cluster-1-monitor]
+type=monitor
+module=mysqlmon
+servers=server1,server2,server3
+user=maxuser
+passwd=maxpwd
+monitor_interval=1000
+
+[my-readwrite-service]
+type=service
+router=readwritesplit
+monitor=db-cluster-1-monitor
+user=maxuser
+passwd=maxpwd
+```
+
+The _db-cluster-1-monitor_ cluster consists of three servers monitored by a
+_mysqlmon_ monitor module. The _my-readwrite-service_ uses this monitor as the
+source for servers.
+
 #### `servers`
 
 The servers parameter in a service definition provides a comma separated list of

Documentation/Release-Notes/MaxScale-2.1.0-Release-Notes.md

@@ -158,6 +158,15 @@ following new commands were added to maxadmin, see output of `maxadmin help
 With these new features, you can start MaxScale without the servers and define
 them later.
 
+### Monitors as server sources for services
+
+Services now accept a `monitor` parameter which can be used to point a service
+to a cluster of servers that are monitored by a monitor. The value of the
+`monitor` parameter should be the name of a monitor in the configuration name.
+
+For more details, refer to the [Configuration
+Guide](../Getting-Started/Configuration-Guide.md#cluster) section on clusters.
+
 ### Module commands
 
 Introduced in MaxScale 2.1, the module commands are special, module-specific

server/core/config.c

@@ -119,6 +119,7 @@ static const char *service_params[] =
     "router",
     "router_options",
     "servers",
+    "monitor",
     "user",
     "passwd", // DEPRECATE: See config_get_password.
     "password",
@@ -2800,16 +2801,45 @@ int configure_new_service(CONFIG_CONTEXT *context, CONFIG_CONTEXT *obj)
     int error_count = 0;
     char *filters = config_get_value(obj->parameters, "filters");
     char *servers = config_get_value(obj->parameters, "servers");
+    char *monitor = config_get_value(obj->parameters, "monitor");
     char *roptions = config_get_value(obj->parameters, "router_options");
-    char *router = config_get_value(obj->parameters, "router");
     SERVICE *service = obj->element;
 
     if (service)
     {
+        if (monitor)
+        {
+            if (servers)
+            {
+                MXS_WARNING("Both `monitor` and `servers` are defined. Only the "
+                            "value of `monitor` will be used.");
+            }
+
+            /** `monitor` takes priority over `servers` */
+            servers = NULL;
+
+            for (CONFIG_CONTEXT *ctx = context; ctx; ctx = ctx->next)
+            {
+                if (strcmp(ctx->object, monitor) == 0)
+                {
+                    servers = config_get_value(ctx->parameters, "servers");
+                    break;
+                }
+            }
+
+            if (servers == NULL)
+            {
+                MXS_ERROR("Unable to find monitor '%s'.", monitor);
+                error_count++;
+            }
+        }
+
         if (servers)
         {
+            char srv_list[strlen(servers) + 1];
+            strcpy(srv_list, servers);
             char *lasts;
-            char *s = strtok_r(servers, ",", &lasts);
+            char *s = strtok_r(srv_list, ",", &lasts);
             while (s)
             {
                 CONFIG_CONTEXT *obj1 = context;
@@ -2820,6 +2850,7 @@ int configure_new_service(CONFIG_CONTEXT *context, CONFIG_CONTEXT *obj)
                     {
                         found = 1;
                         serviceAddBackend(service, obj1->element);
+                        break;
                     }
                     obj1 = obj1->next;
                 }