753 lines
25 KiB
C++
753 lines
25 KiB
C++
/*
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* Copyright (c) 2016 MariaDB Corporation Ab
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*
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* Use of this software is governed by the Business Source License included
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* in the LICENSE.TXT file and at www.mariadb.com/bsl11.
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*
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* Change Date: 2022-01-01
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*
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* On the date above, in accordance with the Business Source License, use
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* of this software will be governed by version 2 or later of the General
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* Public License.
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*/
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/**
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* @file readconnroute.c - Read Connection Load Balancing Query Router
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*
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* This is the implementation of a simple query router that balances
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* read connections. It assumes the service is configured with a set
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* of slaves and that the application clients already split read and write
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* queries. It offers a service to balance the client read connections
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* over this set of slave servers. It does this once only, at the time
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* the connection is made. It chooses the server that currently has the least
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* number of connections by keeping a count for each server of how
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* many connections the query router has made to the server.
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*
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* When two servers have the same number of current connections the one with
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* the least number of connections since startup will be used.
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*
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* The router may also have options associated to it that will limit the
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* choice of backend server. Currently two options are supported, the "master"
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* option will cause the router to only connect to servers marked as masters
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* and the "slave" option will limit connections to routers that are marked
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* as slaves. If neither option is specified the router will connect to either
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* masters or slaves.
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*
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* @verbatim
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* Revision History
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*
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* Date Who Description
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* 14/06/2013 Mark Riddoch Initial implementation
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* 25/06/2013 Mark Riddoch Addition of checks for current server state
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* 26/06/2013 Mark Riddoch Use server with least connections since
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* startup if the number of current
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* connections is the same for two servers
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* Addition of master and slave options
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* 27/06/2013 Vilho Raatikka Added skygw_log_write command as an example
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* and necessary headers.
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* 17/07/2013 Massimiliano Pinto Added clientReply routine:
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* called by backend server to send data to client
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* Included maxscale/protocol/mysql.h
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* with macros and MySQL commands with MYSQL_ prefix
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* avoiding any conflict with the standard ones
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* in mysql.h
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* 22/07/2013 Mark Riddoch Addition of joined router option for Galera
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* clusters
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* 31/07/2013 Massimiliano Pinto Added a check for candidate server, if NULL return
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* 12/08/2013 Mark Riddoch Log unsupported router options
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* 04/09/2013 Massimiliano Pinto Added client NULL check in clientReply
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* 22/10/2013 Massimiliano Pinto errorReply called from backend, for client error reply
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* or take different actions such as open a new backend connection
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* 20/02/2014 Massimiliano Pinto If router_options=slave, route traffic to master if no slaves available
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* 06/03/2014 Massimiliano Pinto Server connection counter is now updated in closeSession
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* 24/06/2014 Massimiliano Pinto New rules for selecting the Master server
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* 27/06/2014 Mark Riddoch Addition of server weighting
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* 11/06/2015 Martin Brampton Remove decrement n_current (moved to dcb.c)
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* 09/09/2015 Martin Brampton Modify error handler
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* 25/09/2015 Martin Brampton Block callback processing when no router session in the DCB
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* 09/11/2015 Martin Brampton Modified routeQuery - must free "queue" regardless of outcome
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*
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* @endverbatim
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*/
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#include "readconnection.hh"
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <signal.h>
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#include <string>
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#include <vector>
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#include <maxscale/alloc.h>
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#include <maxscale/server.hh>
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#include <maxscale/router.hh>
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#include <maxbase/atomic.hh>
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#include <maxscale/dcb.hh>
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#include <maxscale/modinfo.h>
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#include <maxscale/log.h>
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#include <maxscale/protocol/mysql.h>
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#include <maxscale/modutil.hh>
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#include <maxscale/utils.hh>
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/* The router entry points */
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static MXS_ROUTER* createInstance(SERVICE* service, MXS_CONFIG_PARAMETER* params);
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static MXS_ROUTER_SESSION* newSession(MXS_ROUTER* instance, MXS_SESSION* session);
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static void closeSession(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session);
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static void freeSession(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session);
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static int routeQuery(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session, GWBUF* queue);
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static void diagnostics(MXS_ROUTER* instance, DCB* dcb);
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static json_t* diagnostics_json(const MXS_ROUTER* instance);
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static void clientReply(MXS_ROUTER* instance,
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MXS_ROUTER_SESSION* router_session,
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GWBUF* queue,
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DCB* backend_dcb);
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static void handleError(MXS_ROUTER* instance,
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MXS_ROUTER_SESSION* router_session,
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GWBUF* errbuf,
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DCB* problem_dcb,
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mxs_error_action_t action,
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bool* succp);
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static uint64_t getCapabilities(MXS_ROUTER* instance);
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static bool configureInstance(MXS_ROUTER* instance, MXS_CONFIG_PARAMETER* params);
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static SERVER_REF* get_root_master(SERVER_REF* servers);
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/**
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* The module entry point routine. It is this routine that
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* must populate the structure that is referred to as the
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* "module object", this is a structure with the set of
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* external entry points for this module.
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*
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* @return The module object
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*/
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extern "C" MXS_MODULE* MXS_CREATE_MODULE()
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{
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MXS_NOTICE("Initialise readconnroute router module.");
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static MXS_ROUTER_OBJECT MyObject =
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{
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createInstance,
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newSession,
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closeSession,
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freeSession,
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routeQuery,
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diagnostics,
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diagnostics_json,
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clientReply,
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handleError,
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getCapabilities,
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NULL,
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configureInstance
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};
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static MXS_MODULE info =
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{
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MXS_MODULE_API_ROUTER,
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MXS_MODULE_GA,
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MXS_ROUTER_VERSION,
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"A connection based router to load balance based on connections",
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"V2.0.0",
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RCAP_TYPE_RUNTIME_CONFIG,
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&MyObject,
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NULL, /* Process init. */
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NULL, /* Process finish. */
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NULL, /* Thread init. */
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NULL, /* Thread finish. */
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{
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{MXS_END_MODULE_PARAMS}
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}
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};
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return &info;
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}
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static inline void free_readconn_instance(ROUTER_INSTANCE* router)
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{
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if (router)
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{
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MXS_FREE(router);
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}
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}
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static bool configureInstance(MXS_ROUTER* instance, MXS_CONFIG_PARAMETER* params)
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{
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ROUTER_INSTANCE* inst = static_cast<ROUTER_INSTANCE*>(instance);
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uint64_t bitmask = 0;
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uint64_t bitvalue = 0;
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bool ok = true;
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for (const auto& opt : mxs::strtok(config_get_string(params, "router_options"), ", \t"))
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{
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if (!strcasecmp(opt.c_str(), "master"))
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{
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bitmask |= (SERVER_MASTER | SERVER_SLAVE);
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bitvalue |= SERVER_MASTER;
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}
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else if (!strcasecmp(opt.c_str(), "slave"))
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{
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bitmask |= (SERVER_MASTER | SERVER_SLAVE);
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bitvalue |= SERVER_SLAVE;
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}
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else if (!strcasecmp(opt.c_str(), "running"))
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{
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bitmask |= (SERVER_RUNNING);
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bitvalue |= SERVER_RUNNING;
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}
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else if (!strcasecmp(opt.c_str(), "synced"))
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{
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bitmask |= (SERVER_JOINED);
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bitvalue |= SERVER_JOINED;
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}
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else if (!strcasecmp(opt.c_str(), "ndb"))
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{
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bitmask |= (SERVER_NDB);
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bitvalue |= SERVER_NDB;
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}
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else
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{
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MXS_ERROR("Unsupported router option \'%s\' for readconnroute. "
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"Expected router options are [slave|master|synced|ndb|running]",
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opt.c_str());
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ok = false;
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}
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}
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if (bitmask == 0 && bitvalue == 0)
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{
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/** No parameters given, use RUNNING as a valid server */
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bitmask |= (SERVER_RUNNING);
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bitvalue |= SERVER_RUNNING;
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}
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if (ok)
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{
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uint64_t mask = bitmask | (bitvalue << 32);
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atomic_store_uint64(&inst->bitmask_and_bitvalue, mask);
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}
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return ok;
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}
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/**
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* Create an instance of the router for a particular service
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* within the gateway.
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*
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* @param service The service this router is being create for
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* @param options An array of options for this query router
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*
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* @return The instance data for this new instance
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*/
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static MXS_ROUTER* createInstance(SERVICE* service, MXS_CONFIG_PARAMETER* params)
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{
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ROUTER_INSTANCE* inst = static_cast<ROUTER_INSTANCE*>(MXS_CALLOC(1, sizeof(ROUTER_INSTANCE)));
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if (inst)
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{
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inst->service = service;
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inst->bitmask_and_bitvalue = 0;
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if (!configureInstance((MXS_ROUTER*)inst, params))
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{
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free_readconn_instance(inst);
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inst = nullptr;
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}
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}
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return (MXS_ROUTER*)inst;
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}
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/**
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* Associate a new session with this instance of the router.
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*
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* @param instance The router instance data
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* @param session The session itself
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* @return Session specific data for this session
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*/
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static MXS_ROUTER_SESSION* newSession(MXS_ROUTER* instance, MXS_SESSION* session)
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{
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ROUTER_INSTANCE* inst = (ROUTER_INSTANCE*) instance;
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ROUTER_CLIENT_SES* client_rses;
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SERVER_REF* candidate = NULL;
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SERVER_REF* master_host = NULL;
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MXS_DEBUG("%lu [newSession] new router session with session "
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"%p, and inst %p.",
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pthread_self(),
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session,
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inst);
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client_rses = (ROUTER_CLIENT_SES*) MXS_CALLOC(1, sizeof(ROUTER_CLIENT_SES));
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if (client_rses == NULL)
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{
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return NULL;
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}
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client_rses->client_dcb = session->client_dcb;
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uint64_t mask = atomic_load_uint64(&inst->bitmask_and_bitvalue);
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client_rses->bitmask = mask;
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client_rses->bitvalue = mask >> 32;
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/**
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* Find the Master host from available servers
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*/
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master_host = get_root_master(inst->service->dbref);
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/**
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* Find a backend server to connect to. This is the extent of the
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* load balancing algorithm we need to implement for this simple
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* connection router.
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*/
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/*
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* Loop over all the servers and find any that have fewer connections
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* than the candidate server.
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*
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* If a server has less connections than the current candidate we mark this
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* as the new candidate to connect to.
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*
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* If a server has the same number of connections currently as the candidate
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* and has had less connections over time than the candidate it will also
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* become the new candidate. This has the effect of spreading the
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* connections over different servers during periods of very low load.
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*/
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for (SERVER_REF* ref = inst->service->dbref; ref; ref = ref->next)
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{
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if (!SERVER_REF_IS_ACTIVE(ref) || server_is_in_maint(ref->server))
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{
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continue;
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}
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/* Check server status bits against bitvalue from router_options */
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if (ref && server_is_usable(ref->server)
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&& (ref->server->status & client_rses->bitmask & client_rses->bitvalue))
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{
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if (master_host)
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{
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if (ref == master_host
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&& (client_rses->bitvalue & (SERVER_SLAVE | SERVER_MASTER)) == SERVER_SLAVE)
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{
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/* Skip root master here, as it could also be slave of an external server that
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* is not in the configuration. Intermediate masters (Relay Servers) are also
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* slave and will be selected as Slave(s)
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*/
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continue;
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}
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if (ref == master_host && client_rses->bitvalue == SERVER_MASTER)
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{
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/* If option is "master" return only the root Master as there could be
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* intermediate masters (Relay Servers) and they must not be selected.
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*/
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candidate = master_host;
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break;
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}
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}
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else if (client_rses->bitvalue == SERVER_MASTER)
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{
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/* Master_host is NULL, no master server. If requested router_option is 'master'
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* candidate will be NULL.
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*/
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candidate = NULL;
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break;
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}
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/* If no candidate set, set first running server as our initial candidate server */
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if (candidate == NULL)
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{
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candidate = ref;
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}
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else if (ref->server_weight == 0 || candidate->server_weight == 0)
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{
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if (ref->server_weight) // anything with a weight is better
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{
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candidate = ref;
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}
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}
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else if ((ref->connections + 1) / ref->server_weight
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< (candidate->connections + 1) / candidate->server_weight)
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{
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/* ref has a better score. */
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candidate = ref;
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}
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}
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}
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/* If we haven't found a proper candidate yet but a master server is available, we'll pick that
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* with the assumption that it is "better" than a slave.
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*/
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if (!candidate)
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{
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if (master_host)
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{
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candidate = master_host;
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// Even if we had 'router_options=slave' in the configuration file, we
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// will still end up here if there are no slaves, but a sole master. So
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// that the server will be considered valid in connection_is_valid(), we
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// turn on the SERVER_MASTER bit.
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//
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// We must do that so that readconnroute in MaxScale 2.2 will again behave
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// the same way as it did up until 2.1.12.
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if (client_rses->bitvalue & SERVER_SLAVE)
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{
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client_rses->bitvalue |= SERVER_MASTER;
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}
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}
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else
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{
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MXS_ERROR("Failed to create new routing session. Couldn't find eligible"
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" candidate server. Freeing allocated resources.");
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MXS_FREE(client_rses);
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return NULL;
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}
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}
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/*
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* We now have the server with the least connections.
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* Bump the connection count for this server
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*/
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client_rses->backend = candidate;
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/** Open the backend connection */
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client_rses->backend_dcb = dcb_connect(candidate->server,
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session,
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candidate->server->protocol);
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if (client_rses->backend_dcb == NULL)
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{
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/** The failure is reported in dcb_connect() */
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MXS_FREE(client_rses);
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return NULL;
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}
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mxb::atomic::add(&candidate->connections, 1, mxb::atomic::RELAXED);
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inst->stats.n_sessions++;
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MXS_INFO("New session for server %s. Connections : %d",
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candidate->server->name,
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candidate->connections);
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return reinterpret_cast<MXS_ROUTER_SESSION*>(client_rses);
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}
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/**
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* @node Unlink from backend server, unlink from router's connection list,
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* and free memory of a router client session.
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*
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* Parameters:
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* @param router - <usage>
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* <description>
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*
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* @param router_cli_ses - <usage>
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* <description>
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*
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* @return void
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*
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*
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* @details (write detailed description here)
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*
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*/
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static void freeSession(MXS_ROUTER* router_instance, MXS_ROUTER_SESSION* router_client_ses)
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{
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ROUTER_INSTANCE* router = (ROUTER_INSTANCE*) router_instance;
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ROUTER_CLIENT_SES* router_cli_ses = (ROUTER_CLIENT_SES*) router_client_ses;
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MXB_AT_DEBUG(int prev_val = ) mxb::atomic::add(&router_cli_ses->backend->connections,
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-1,
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mxb::atomic::RELAXED);
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mxb_assert(prev_val > 0);
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MXS_FREE(router_cli_ses);
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}
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/**
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* Close a session with the router, this is the mechanism
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* by which a router may cleanup data structure etc.
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*
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* @param instance The router instance data
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* @param router_session The session being closed
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*/
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static void closeSession(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session)
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{
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ROUTER_CLIENT_SES* router_cli_ses = (ROUTER_CLIENT_SES*) router_session;
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mxb_assert(router_cli_ses->backend_dcb);
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dcb_close(router_cli_ses->backend_dcb);
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}
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/** Log routing failure due to closed session */
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static void log_closed_session(mxs_mysql_cmd_t mysql_command, SERVER_REF* ref)
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{
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char msg[MAX_SERVER_ADDRESS_LEN + 200] = ""; // Extra space for message
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if (server_is_down(ref->server))
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{
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sprintf(msg, "Server '%s' is down.", ref->server->name);
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}
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else if (server_is_in_maint(ref->server))
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{
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sprintf(msg, "Server '%s' is in maintenance.", ref->server->name);
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}
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else
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{
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sprintf(msg, "Server '%s' no longer qualifies as a target server.", ref->server->name);
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}
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MXS_ERROR("Failed to route MySQL command %d to backend server. %s", mysql_command, msg);
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}
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/**
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* Check if the server we're connected to is still valid
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*
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* @param inst Router instance
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* @param router_cli_ses Router session
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*
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* @return True if the backend connection is still valid
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*/
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static inline bool connection_is_valid(ROUTER_INSTANCE* inst, ROUTER_CLIENT_SES* router_cli_ses)
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{
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bool rval = false;
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// inst->bitvalue and router_cli_ses->bitvalue are different, if we had
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// 'router_options=slave' in the configuration file and there was only
|
|
// the sole master available at session creation time.
|
|
|
|
if (server_is_usable(router_cli_ses->backend->server)
|
|
&& (router_cli_ses->backend->server->status & router_cli_ses->bitmask & router_cli_ses->bitvalue))
|
|
{
|
|
// Note the use of '==' and not '|'. We must use the former to exclude a
|
|
// 'router_options=slave' that uses the master due to no slave having been
|
|
// available at session creation time. Its bitvalue is (SERVER_MASTER | SERVER_SLAVE).
|
|
if ((router_cli_ses->bitvalue == SERVER_MASTER) && router_cli_ses->backend->active)
|
|
{
|
|
// If we're using an active master server, verify that it is still a master
|
|
rval = router_cli_ses->backend == get_root_master(inst->service->dbref);
|
|
}
|
|
else
|
|
{
|
|
/**
|
|
* Either we don't use master type servers or the server reference
|
|
* is deactivated. We let deactivated connection close gracefully
|
|
* so we simply assume it is OK. This allows a server to be taken
|
|
* out of use in a manner that won't cause errors to the connected
|
|
* clients.
|
|
*/
|
|
rval = true;
|
|
}
|
|
}
|
|
|
|
return rval;
|
|
}
|
|
|
|
/**
|
|
* We have data from the client, we must route it to the backend.
|
|
* This is simply a case of sending it to the connection that was
|
|
* chosen when we started the client session.
|
|
*
|
|
* @param instance The router instance
|
|
* @param router_session The router session returned from the newSession call
|
|
* @param queue The queue of data buffers to route
|
|
* @return if succeed 1, otherwise 0
|
|
*/
|
|
static int routeQuery(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session, GWBUF* queue)
|
|
{
|
|
ROUTER_INSTANCE* inst = (ROUTER_INSTANCE*) instance;
|
|
ROUTER_CLIENT_SES* router_cli_ses = (ROUTER_CLIENT_SES*) router_session;
|
|
int rc = 0;
|
|
MySQLProtocol* proto = (MySQLProtocol*)router_cli_ses->client_dcb->protocol;
|
|
mxs_mysql_cmd_t mysql_command = proto->current_command;
|
|
|
|
mxb::atomic::add(&inst->stats.n_queries, 1, mxb::atomic::RELAXED);
|
|
|
|
// Due to the streaming nature of readconnroute, this is not accurate
|
|
mxb::atomic::add(&router_cli_ses->backend->server->stats.packets, 1, mxb::atomic::RELAXED);
|
|
|
|
DCB* backend_dcb = router_cli_ses->backend_dcb;
|
|
mxb_assert(backend_dcb);
|
|
char* trc = NULL;
|
|
|
|
if (!connection_is_valid(inst, router_cli_ses))
|
|
{
|
|
log_closed_session(mysql_command, router_cli_ses->backend);
|
|
gwbuf_free(queue);
|
|
return rc;
|
|
}
|
|
|
|
switch (mysql_command)
|
|
{
|
|
case MXS_COM_CHANGE_USER:
|
|
rc = backend_dcb->func.auth(backend_dcb,
|
|
NULL,
|
|
backend_dcb->session,
|
|
queue);
|
|
break;
|
|
|
|
case MXS_COM_QUERY:
|
|
if (mxs_log_is_priority_enabled(LOG_INFO))
|
|
{
|
|
trc = modutil_get_SQL(queue);
|
|
}
|
|
|
|
default:
|
|
rc = backend_dcb->func.write(backend_dcb, queue);
|
|
break;
|
|
}
|
|
|
|
MXS_INFO("Routed [%s] to '%s'%s%s",
|
|
STRPACKETTYPE(mysql_command),
|
|
backend_dcb->server->name,
|
|
trc ? ": " : ".",
|
|
trc ? trc : "");
|
|
MXS_FREE(trc);
|
|
|
|
return rc;
|
|
}
|
|
|
|
/**
|
|
* Display router diagnostics
|
|
*
|
|
* @param instance Instance of the router
|
|
* @param dcb DCB to send diagnostics to
|
|
*/
|
|
static void diagnostics(MXS_ROUTER* router, DCB* dcb)
|
|
{
|
|
ROUTER_INSTANCE* router_inst = (ROUTER_INSTANCE*) router;
|
|
const char* weightby = serviceGetWeightingParameter(router_inst->service);
|
|
|
|
dcb_printf(dcb,
|
|
"\tNumber of router sessions: %d\n",
|
|
router_inst->stats.n_sessions);
|
|
dcb_printf(dcb,
|
|
"\tCurrent no. of router sessions: %d\n",
|
|
router_inst->service->stats.n_current);
|
|
dcb_printf(dcb,
|
|
"\tNumber of queries forwarded: %d\n",
|
|
router_inst->stats.n_queries);
|
|
if (*weightby)
|
|
{
|
|
dcb_printf(dcb,
|
|
"\tConnection distribution based on %s "
|
|
"server parameter.\n",
|
|
weightby);
|
|
dcb_printf(dcb,
|
|
"\t\tServer Target %% Connections\n");
|
|
for (SERVER_REF* ref = router_inst->service->dbref; ref; ref = ref->next)
|
|
{
|
|
dcb_printf(dcb,
|
|
"\t\t%-20s %3.1f%% %d\n",
|
|
ref->server->name,
|
|
ref->server_weight * 100,
|
|
ref->connections);
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Display router diagnostics
|
|
*
|
|
* @param instance Instance of the router
|
|
* @param dcb DCB to send diagnostics to
|
|
*/
|
|
static json_t* diagnostics_json(const MXS_ROUTER* router)
|
|
{
|
|
ROUTER_INSTANCE* router_inst = (ROUTER_INSTANCE*)router;
|
|
json_t* rval = json_object();
|
|
|
|
json_object_set_new(rval, "connections", json_integer(router_inst->stats.n_sessions));
|
|
json_object_set_new(rval, "current_connections", json_integer(router_inst->service->stats.n_current));
|
|
json_object_set_new(rval, "queries", json_integer(router_inst->stats.n_queries));
|
|
|
|
const char* weightby = serviceGetWeightingParameter(router_inst->service);
|
|
|
|
if (*weightby)
|
|
{
|
|
json_object_set_new(rval, "weightby", json_string(weightby));
|
|
}
|
|
|
|
return rval;
|
|
}
|
|
|
|
/**
|
|
* Client Reply routine
|
|
*
|
|
* The routine will reply to client data from backend server
|
|
*
|
|
* @param instance The router instance
|
|
* @param router_session The router session
|
|
* @param backend_dcb The backend DCB
|
|
* @param queue The GWBUF with reply data
|
|
*/
|
|
static void clientReply(MXS_ROUTER* instance,
|
|
MXS_ROUTER_SESSION* router_session,
|
|
GWBUF* queue,
|
|
DCB* backend_dcb)
|
|
{
|
|
mxb_assert(backend_dcb->session->client_dcb != NULL);
|
|
MXS_SESSION_ROUTE_REPLY(backend_dcb->session, queue);
|
|
}
|
|
|
|
/**
|
|
* Error Handler routine
|
|
*
|
|
* The routine will handle errors that occurred in writes.
|
|
*
|
|
* @param instance The router instance
|
|
* @param router_session The router session
|
|
* @param message The error message to reply
|
|
* @param problem_dcb The DCB related to the error
|
|
* @param action The action: ERRACT_NEW_CONNECTION or ERRACT_REPLY_CLIENT
|
|
* @param succp Result of action: true if router can continue
|
|
*
|
|
*/
|
|
static void handleError(MXS_ROUTER* instance,
|
|
MXS_ROUTER_SESSION* router_session,
|
|
GWBUF* errbuf,
|
|
DCB* problem_dcb,
|
|
mxs_error_action_t action,
|
|
bool* succp)
|
|
|
|
{
|
|
mxb_assert(problem_dcb->dcb_role == DCB_ROLE_BACKEND_HANDLER);
|
|
mxb_assert(problem_dcb->session->state == SESSION_STATE_ROUTER_READY);
|
|
DCB* client_dcb = problem_dcb->session->client_dcb;
|
|
client_dcb->func.write(client_dcb, gwbuf_clone(errbuf));
|
|
|
|
// The DCB will be closed once the session closes, no need to close it here
|
|
*succp = false;
|
|
}
|
|
|
|
static uint64_t getCapabilities(MXS_ROUTER* instance)
|
|
{
|
|
return RCAP_TYPE_RUNTIME_CONFIG;
|
|
}
|
|
|
|
/*
|
|
* This routine returns the master server from a MariaDB replication tree. The server must be
|
|
* running, not in maintenance and have the master bit set. If multiple masters are found,
|
|
* the one with the highest weight is chosen.
|
|
*
|
|
* @param servers The list of servers
|
|
* @return The Master server
|
|
*
|
|
*/
|
|
|
|
static SERVER_REF* get_root_master(SERVER_REF* servers)
|
|
{
|
|
SERVER_REF* master_host = NULL;
|
|
for (SERVER_REF* ref = servers; ref; ref = ref->next)
|
|
{
|
|
if (ref->active && server_is_master(ref->server))
|
|
{
|
|
// No master found yet or this one has better weight.
|
|
if (master_host == NULL || ref->server_weight > master_host->server_weight)
|
|
{
|
|
master_host = ref;
|
|
}
|
|
}
|
|
}
|
|
return master_host;
|
|
}
|