Monitoring Galera with MONyog

Transcription

1 Monitoring Galera with MONyog Abstract This white paper introduces the drawbacks of traditional MySQL High Availability set ups and suggests a modern, best- in- class High Availability solution utilising MONyog and Galera. The basics of Galera and MONyog are explained, and the steps to setting up the combined solution is gone through step- by- step. 1 Introduction A key aspect of managing a database system is being able to monitor it, review the key parameters and performance metrics over time, send alerts when there are issues and identify bottlenecks. One of the most well- known and respected products for monitoring MySQL is MONyog. For customers with a support subscription from MariaDB, MONyog is a key differentiator.. Similarly, High Availability (HA) of database systems have matured and become much more affordable, now providing 24x7 database connectivity for your mission- critical applications. In the past, MySQL HA was based on expensive, legacy availability solutions that used physical storage or MySQL Replication. Both of these solutions have drawbacks: Whilst a storage- based solution offers redundancy of the physical media it does not allow more than one MySQL instance to access storage at the same time. This makes for slow failover. MySQL Replication uses a complex Asynchronous or Semi- synchronous setup. This means that failover has to wait for the replication to catch up. Allowing multiple masters when using MySQL Replication is possible, but it can be unreliable and there is no conflict detection. At MariaDB, we believe that MONyog combined with Galera overcomes this issues to provide a modern, best- in- class High Availability solution for MySQL users. 2 Introduction to High Availability with Galera Galera uses a software- only configuration that provides the same level of data assurance as a Storage Based solution, but is tightly integrated with MySQL so setting up and managing a Galera- based cluster is easy. Galera does the actual replication externally to MySQL, but this is just a library that is called from the database server, so there are no new servers to run. Configuring Galera takes place in the same way as configuring MySQL - by using a my.cnf file. Galera creates a true cluster which is different from using MySQL Replication, for example, where the different nodes are largely autonomous. With Galera, all nodes know about each other, they exchange information and perform arbitration so that quorum is achieved and split- brain situations are avoided. The status of a Galera cluster is provided in the same way as for MySQL variables and status, i.e. by running the commands SHOW VARIABLES and SHOW STATUS. Galera also supports Conflict Resolution using Optimistic Locking, providing low latency and consistent data, while maintaining high performance. Page 1

2 3 Introduction to MONyog MONyog is a powerful tool for monitoring MySQL and related database technologies. It includes features that store performance data and settings, customize the data that is retrieved, graph data over time and send alerts. Its also contains a knowledge base so a user of the system is understands what all the metrics mean and, when there is an alert, suggest appropriate actions. Since it runs as a web service, MONyog is accessible from any browser, which limits installation requirements to one machine only. Written in C/C++ in the lower layers, MONyog s user Interface is AJAX- based to allow for responsive and effective interaction. MONyog is also user- extensible and exposes its data as JavaScript. This means that adding user- defined objects is easy and uses familiar technologies. Best of all, MONyog is already pre- configured to handle monitoring of a Galera- based MySQL cluster. 4 Monitoring MySQL / MariaDB Galera Cluster with MONyog The following assumes that you have already installed and started MONYog (version 5.53 or later), and you have a few Galera enabled MySQL servers running. In the examples shown here, we will use a simple Galera Cluster with just 2 nodes, ClusterNode41 and ClusterNode Enable the Galera monitors in MONyog Monitoring Galera has been supported by MONyog for some time but it is not enabled by default so to get started we need to enable Galera monitoring: Log into MONyog and click in the Customize button at the top left of the window. You now see a two lists of monitor groups, the enabled ones to the left and the disabled to the right. Select the Galera monitor group in the left- hand list and then click the button Enable in between the two lists. Page 2

3 With the monitors in place, we can now start to do some more interesting things. 4.2 Creating Galera Dashboard graphs One of the first things you will probably want is to have a graph on the health of your MySQL cluster. Right now the Galera component of MONyog only contains monitors, but creating graphs is easy. Let s create a graph that shows if there is a bottleneck in the replication between the Galera nodes, which can be seen by monitoring the status variable wsrep_local_send_queue_avg: Go to the Dashboard pane and then click on the cogwheel settings icon on the top right and select Add new Dashboard Chart. Then you set the Caption of the chart and the graph (there is just 1) and then the tricky bit, the value to monitor (in Series Values): [MONyog.MySQL.GlobalStatus.wsrep_local_send_queue_avg]. Finally, you probably want to set ChartValue to Current in this case. The screen should look some- thing like this: With this in place, let s now add a second Chart, this time showing the percentage of the time that Galera replication is paused. To do this, create the Graph in the same way as above, choosing appropriate names again, but in Series Values you instead put: [ToInt(MONyog.MySQL.GlobalStatus.wsrep_fl ow_control_paused) * 100] Page 3

4 With these two new Graphs in place, and a few existing ones removed, the Dashboard now looks like this: 4.3 Creating MONyog Alerts for Galera A very important aspect of monitoring is to be able to defi ne alerts when certain conditions happen. By default, the Galera monitors have one alert on the wsrep_ready status variable. A useful alert would be on the wsrep_cluster_size variable, as this allows us to warn when there is just 1 (or 2) nodes in the cluster. This can be achieved doing the following: Go to the Monitors pane and click on the Number of nodes in the cluster monitor in the Galera group. In the popup window you get, click on Customize and you get a window where this monitor can be confi gured. At the top of this window, click on the View Advanced link and scroll down to the Alert settings. Alter condition can be set to something like this: function() { if(this.value < 2) return Critical ; else if (this.value < 3) return Warning ; else return None ; } Page 4

5 To alert for a critical condition when there is just 1 server in the cluster and issue a warning if there are 2. To get notified of this condition, you also have to set Notify? To Yes. In addition you have to do two more general things to enable notifications in general: Click on Tools in the left menu pane and then set up Mail Settings. Enable the monitored server to send alerts by selecting Edit server in the dropdown menu to the right of the server in the left list, and then go to the Notifications tab and enable Send notifications over Mail (SMTP). 5 References MariaDB provides subscriptions for MySQL / MariaDB and Galera that includes MONyog: Codership develops Galera: Webyog develops database tools, among the MONyog: Page 5