From d5d41349aee235e12253df52c3ab9ee900719e0b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus.makela@mariadb.com>
Date: Mon, 20 Nov 2017 11:16:52 +0200
Subject: [PATCH] MXS-1509: Add `ignore_external_masters` parameter

The new parameter allows ignoring of master servers that are external to
the monitor configuration. This allows sub-trees of the actual replication
tree to be used as fully fledged replication trees.
---
 Documentation/Monitors/MySQL-Monitor.md     | 17 +++++++++++++++++
 include/maxscale/server.h                   |  4 ++++
 server/modules/monitor/mysqlmon.h           |  1 +
 server/modules/monitor/mysqlmon/mysql_mon.c | 15 +++++++++++++++
 4 files changed, 37 insertions(+)

diff --git a/Documentation/Monitors/MySQL-Monitor.md b/Documentation/Monitors/MySQL-Monitor.md
index e49459e59..6afe4dca6 100644
--- a/Documentation/Monitors/MySQL-Monitor.md
+++ b/Documentation/Monitors/MySQL-Monitor.md
@@ -120,6 +120,23 @@ This functionality is similar to the [Multi-Master Monitor](MM-Monitor.md)
 functionality. The only difference is that the MySQL monitor will also detect
 traditional Master-Slave topologies.
 
+### `ignore_external_masters`
+
+Ignore any servers that are not monitored by this monitor but are a part of the
+replication topology. This option was added in MaxScale 2.1.12 and is disabled
+by default.
+
+MaxScale detects if a master server replicates from an external server. When
+this is detected, the server is assigned the `Slave` and `Slave of External
+Server` labels and will be treated as a slave server. Most of the time this
+topology is used when MaxScale is used for read scale-out without master
+servers, a Galera cluster with read replicas being a prime example of this
+setup. Sometimes this is not the desired behavior and the external master server
+should be ignored. Most of the time this is due to multi-source replication.
+
+When this option is enabled, all servers that have the `Master, Slave, Slave of
+External Server, Running` labels will instead get the `Master, Running` labels.
+
 ### `detect_standalone_master`
 
 Detect standalone master servers. This feature takes a boolean parameter and is
diff --git a/include/maxscale/server.h b/include/maxscale/server.h
index acbce95be..2fb6e4e77 100644
--- a/include/maxscale/server.h
+++ b/include/maxscale/server.h
@@ -192,6 +192,10 @@ enum
     (((server)->status & (SERVER_RUNNING|SERVER_MASTER|SERVER_SLAVE|SERVER_MAINT)) == \
      (SERVER_RUNNING|SERVER_MASTER|SERVER_SLAVE))
 
+#define SERVER_IS_SLAVE_OF_EXTERNAL_MASTER(s) (((s)->status & \
+    (SERVER_RUNNING|SERVER_SLAVE_OF_EXTERNAL_MASTER)) == \
+    (SERVER_RUNNING|SERVER_SLAVE_OF_EXTERNAL_MASTER))
+
 /**
  * @brief Allocate a new server
  *
diff --git a/server/modules/monitor/mysqlmon.h b/server/modules/monitor/mysqlmon.h
index ae000150d..1ec15e505 100644
--- a/server/modules/monitor/mysqlmon.h
+++ b/server/modules/monitor/mysqlmon.h
@@ -66,6 +66,7 @@ typedef struct
     bool detectStaleMaster; /**< Monitor flag for MySQL replication Stale Master detection */
     bool detectStaleSlave; /**< Monitor flag for MySQL replication Stale Master detection */
     bool multimaster; /**< Detect and handle multi-master topologies */
+    bool ignore_external_masters; /**< Ignore masters outside of the monitor configuration */
     int disableMasterFailback; /**< Monitor flag for Galera Cluster Master failback */
     int availableWhenDonor; /**< Monitor flag for Galera Cluster Donor availability */
     int disableMasterRoleSetting; /**< Monitor flag to disable setting master role */
diff --git a/server/modules/monitor/mysqlmon/mysql_mon.c b/server/modules/monitor/mysqlmon/mysql_mon.c
index 5abab0601..14226c14b 100644
--- a/server/modules/monitor/mysqlmon/mysql_mon.c
+++ b/server/modules/monitor/mysqlmon/mysql_mon.c
@@ -129,6 +129,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
             {"detect_standalone_master", MXS_MODULE_PARAM_BOOL, "false"},
             {"failcount", MXS_MODULE_PARAM_COUNT, "5"},
             {"allow_cluster_recovery", MXS_MODULE_PARAM_BOOL, "true"},
+            {"ignore_external_masters", MXS_MODULE_PARAM_BOOL, "false"},
             {
                 "script",
                 MXS_MODULE_PARAM_PATH,
@@ -280,6 +281,7 @@ startMonitor(MXS_MONITOR *monitor, const MXS_CONFIG_PARAMETER* params)
     handle->detectStaleSlave = config_get_bool(params, "detect_stale_slave");
     handle->replicationHeartbeat = config_get_bool(params, "detect_replication_lag");
     handle->multimaster = config_get_bool(params, "multimaster");
+    handle->ignore_external_masters = config_get_bool(params, "ignore_external_masters");
     handle->detect_standalone_master = config_get_bool(params, "detect_standalone_master");
     handle->failcount = config_get_integer(params, "failcount");
     handle->allow_cluster_recovery = config_get_bool(params, "allow_cluster_recovery");
@@ -1338,6 +1340,19 @@ monitorMain(void *arg)
             }
         }
 
+        /**
+         * Clear external slave status from master if configured to do so.
+         * This allows parts of a multi-tiered replication setup to be used
+         * in MaxScale.
+         */
+        if (root_master && SERVER_IS_SLAVE_OF_EXTERNAL_MASTER(root_master->server) &&
+            SERVER_IS_MASTER(root_master->server) && handle->ignore_external_masters)
+        {
+            monitor_clear_pending_status(root_master,
+                                         SERVER_SLAVE | SERVER_SLAVE_OF_EXTERNAL_MASTER);
+            server_clear_status_nolock(root_master->server, SERVER_SLAVE | SERVER_SLAVE_OF_EXTERNAL_MASTER);
+        }
+
         /**
          * After updating the status of all servers, check if monitor events
          * need to be launched.