July 25, 2014

High availability for MySQL on Amazon EC2 – Part 3 – Configuring the HA resources

This post is the third of a series that started here.

From the previous of this series, we now have two working EC2 instances that are EBS based. The first instance is the monitor, usually an m1.small type instance and the second instance is hamysql, a large instance type. So far, we have configured Heartbeat for communication between the nodes. Now, it is time to configure the HA resources in Pacemaker. Here are the requirements for the HA resources:

On Monitor

  • Kill the other instance
  • Free the share resources
  • Start a new hamysql instance
  • Reconfigure the clients
  • Give away the resources

On hamysql

  • Run MySQL
  • Monitor MySQL
  • Get out of way if MySQL is not running

From the above requirements, the resource we will create will need to have an “affinity” or preference to run on hamysql. This is accomplished by location directives. I chose to put a weight of 1000 to hamysql and 1 for monitor. Also the resource is obviously not doing the same thing on both hosts so I decided to use a resource of type anything which is just a script. Same script name and path on each host but different content. To configure Pacemaker, assuming both nodes are online, just performs these steps:

Place holders for the resources scripts
On each host:

We will come back in the next posts to these scripts. Then, on one of the host:

and that’s it. We know have a resource which is just a shell script that will preferably run on hamysql but, if hamysql is not available, will be able to run on monitor. That’s the basis we will expand on in the next posts.

About Yves Trudeau

Yves is a Principal Consultant at Percona, specializing in technologies such as MySQL Cluster, Pacemaker and DRBD. He was previously a senior consultant for MySQL and Sun Microsystems. He holds a Ph.D. in Experimental Physics.

Comments

  1. Yves, why use ocf:heartbeat:anything when you could just as well use ocf:heartbeat:mysql with “params binary=/usr/local/bin/mysql”, and actually get MySQL specific resource monitoring?

  2. Florian, waits a bit, you’ll see why later. The mysql script manages instances, not mysql directly.

  3. Jimmy Soho says:

    I’m reading at quite a few places that HA doesn’t work with EC2, but this post suggests it does work. Curious about your next posts..

  4. Jimmy Soho says:

    For example, this article:

    http://agiletesting.blogspot.com/2009/02/load-balancing-in-amazon-ec2-with.html

    “You could use Linux-HA, or Wackamole and the Spread toolkit. However, this is not possible in Amazon EC2 because IP addresses cannot be shared among instances in the manner that heartbeat-type protocols expect.”

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