Take router reconfiguration into use

The router parameters can now be reconfigured at runtime if the router
supports it. Both MaxAdmin and the REST API support it.

server/core/config_runtime.cc

@@ -30,6 +30,7 @@
 #include <maxscale/platform.h>
 #include <maxscale/spinlock.h>
 #include <maxscale/users.h>
+#include <maxscale/router.h>
 
 #include "internal/config.h"
 #include "internal/monitor.h"
@@ -564,6 +565,9 @@ bool runtime_alter_service(SERVICE *service, const char* zKey, const char* zValu
     std::string value(zValue);
     bool valid = false;
 
+    const MXS_MODULE* module = get_module(service->routerModule, MODULE_ROUTER);
+    ss_dassert(module);
+
     spinlock_acquire(&crt_lock);
 
     if (key == CN_USER)
@@ -647,6 +651,33 @@ bool runtime_alter_service(SERVICE *service, const char* zKey, const char* zValu
         valid = true;
         serviceSetRetryOnFailure(service, value.c_str());
     }
+    else if (config_param_is_valid(module->parameters, key.c_str(), value.c_str(), NULL))
+    {
+        if (service->router->configureInstance && service->capabilities & RCAP_TYPE_RUNTIME_CONFIG)
+        {
+            // Stash the old value in case the reconfiguration fails.
+            std::string old_value = config_get_string(service->svc_config_param, key.c_str());
+            ss_dassert(!old_value.empty());
+            service_replace_parameter(service, key.c_str(), value.c_str());
+
+            if (service->router->configureInstance(service->router_instance, service->svc_config_param))
+            {
+                valid = true;
+            }
+            else
+            {
+                // Reconfiguration failed, restore the old value of the parameter
+                service_replace_parameter(service, key.c_str(), old_value.c_str());
+                runtime_error("Reconfiguration of service '%s' failed. See log "
+                              "file for more details.", service->name);
+            }
+        }
+        else
+        {
+            runtime_error("Router '%s' does not support reconfiguration.",
+                          service->routerModule);
+        }
+    }
     else
     {
         runtime_error("Invalid service parameter: %s=%s", key.c_str(), zValue);
@@ -1779,6 +1810,13 @@ bool runtime_alter_service_from_json(SERVICE* service, json_t* new_json)
                 }
             }
 
+            const MXS_MODULE *mod = get_module(service->routerModule, MODULE_ROUTER);
+
+            for (int i = 0; mod->parameters[i].name; i++)
+            {
+                paramset.insert(mod->parameters[i].name);
+            }
+
             const char* key;
             json_t* value;
 
@@ -1801,14 +1839,9 @@ bool runtime_alter_service_from_json(SERVICE* service, json_t* new_json)
                 }
                 else
                 {
-                    const MXS_MODULE *mod = get_module(service->routerModule, MODULE_ROUTER);
                     std::string v = mxs::json_to_string(value);
 
-                    if (config_param_is_valid(mod->parameters, key, v.c_str(), NULL))
-                    {
-                        runtime_error("Runtime modifications to router parameters is not supported: %s=%s", key, v.c_str());
-                    }
-                    else if (!is_dynamic_param(key))
+                    if (!is_dynamic_param(key))
                     {
                         runtime_error("Runtime modifications to static service parameters is not supported: %s=%s", key, v.c_str());
                     }

server/core/internal/service.h

@@ -135,6 +135,15 @@ void  service_update(SERVICE *service, char *router, char *user, char *auth);
  */
 void service_add_parameters(SERVICE *service, const MXS_CONFIG_PARAMETER *param);
 
+/**
+ * @brief Replace service parameter
+ *
+ * @param service Service to modify
+ * @param key     Parameter name
+ * @param value   Parameter value
+ */
+void service_replace_parameter(SERVICE *service, const char* key, const char* value);
+
 /**
  * @brief Set listener rebinding interval
  *

server/core/service.cc

@@ -1773,6 +1773,27 @@ void service_add_parameters(SERVICE *service, const MXS_CONFIG_PARAMETER *param)
     }
 }
 
+void service_add_parameters(SERVICE *service, const char* key, const char* value)
+{
+    MXS_CONFIG_PARAMETER p{const_cast<char*>(key), const_cast<char*>(value), nullptr};
+    service_add_parameters(service, &p);
+}
+
+void service_replace_parameter(SERVICE *service, const char* key, const char* value)
+{
+    for (MXS_CONFIG_PARAMETER* p = service->svc_config_param; p; p = p->next)
+    {
+        if (strcasecmp(p->name, key) == 0)
+        {
+            MXS_FREE(p->value);
+            p->value = MXS_STRDUP_A(value);
+            return;
+        }
+    }
+
+    service_add_parameters(service, key, value);
+}
+
 /*
  * Function to find a string in typelib_t
  * (similar to find_type() of mysys/typelib.c)