MySQL Enterprise Monitor is a tool to watch and analyze multiple MySQL environments from a single web based dashboard. More information is available on the MySQL homepage. Each MySQL instance is monitored by a small agent that connects to the MySQL instance and reads statistics that is sent to the MySQL Enterprise Monitor (MEM) Server.That setup is very easy. But if the MySQL server is in a cluster failover configuration, there are some things to consider when installing the MEM agent:

What do you want?

Do you want to have two entries in the MEM dashboard for both physical servers?This is good because: …

The goal is to have only one entry in the Enterprise Monitor Dashboard that shows the status of the MySQL instance, no matter on which physical server in runs. There are two ways to achieve this:

• You can install the agent on both physical nodes
• You can install the agent on a shared storage.

In either case you have to make sure, that only one agent runs at a time. You have to integrate the agent into your cluster framework. I will not describe how this works, as it is highly dependant on your cluster framework.
The following description assumes, that you will install the agent on both physical nodes.

1. Install the agent but DO NOT START the agent yet.
   
   
2. Edit the [agent-installdir]/etc/mysql-monitor-agent.ini
   In the [mysql-proxy] section add the following line:
   agent-host-id=[logical hostname]
3. …

To install the MEM agent in a way that both physical servers are listed in the MEM dashboard, you have to install the agent on both physical nodes. But: Do not start the agent after the installation!There are three different IDs in MEM: agent-uuid, mysql-uuid and host-id. Usually they are generated automatically and you will never notice these IDs. For more information about the meaning of the different IDs look at this very good explanation from Jonathon Coombes.The agent stores the uuid and the hostid in a MySQL table called mysql.inventory. After a failover the other agent on the new node will notice "wrong" hostid and uuid entries in the inventory table. The agent will stop and ask you to TRUNCATE mysql.inventory. But with this procedure MEM creates a new instance, so all old data is lost. Not good for a failover environment.So in case of a …

What defines instances for the MySQL Enterprise Monitoring (MEM) software and how do they relate to either other and the workings of MEM? 

What defines instances for the MySQL Enterprise Monitoring (MEM) software and how do they relate to either other and the workings of MEM? 

What defines instances for the MySQL Enterprise Monitoring (MEM) software and how do they relate to either other and the workings of MEM?