Installing MySQL (actually MariaDB)
If you wonder why we care about availability sets you better read here
By just having two instances of a database on two different VMs, doesn’t offer much even if the VMs are members of an availability zone. In order to make something out of the configuration of our machines we need the data that our application generates to be replicated between the two databases.
Replication is a quite rich and compilcated subject, the most common replication pattern is the simple master-slave replication in which one “master” node takes care of all the application writes while a number of “slave’ nodes are only reading the data, on top of that basic concept it is also possible to have failover configurations and other desirable characteristics on the DB cluster. The issue in this approach is what will happen if the “master” node fails, and although there might be solutions to that, e.g. having more than one “master” node, here we are having a situation with limited resources and thus we cannot really afford to have sets of master and slave nodes. In our case we would like to follow a master-master configuration where each node is able to accept writes and distribute them throughout the cluster. In this way we can redirect all traffic on one of the VMs we have on Azure, the writes will be replicated also on the second VM and in the case where something happens to the first node, automatically the second one will continue serving the application.