Moving to an A/A cluster

As you will recall from the introduction of Chapter 3, A Closer Look at High Availability, A/A clusters tend to provide higher availability as several nodes are actively running applications at the same time (which, by the way, requires that the necessary data for those applications be available simultaneously on all cluster members). The downside is that if one or more nodes go offline, the remaining ones are assigned extra processing load, thus negatively impacting the overall performance of the cluster.

That being said, let's examine briefly the required steps to convert our current A/P cluster to an A/A one. Make sure a STONITH resource has been defined (refer to chapter 3 for further details).

1. Enable STONITH resource by using the following command:

   pcs property set stonith-enabled=trueInstall
   

2. Install the additional software that will be needed for this:

   yum update && yum install gfs2-utils dlm
   

   As opposed to a traditional journaling filesystem such as ext4...