Data loss recovery and availability



We have got the latest piwik on two EC2 machines running by AWS inside ELB and we have an RDS connected to them. We have got nginx, php-fpm, piwik and redis in each machine. We are using redis to do not write directly to the database and not overload it.
Our question is how much is the availability of such a setup? and how can we improve it?
We also have a concern about downtime data loss. How can we recover the data which are lost during a downtime? Downtime can be caused by anything like a piwik upgrade failure, or redis crash or whatever.

Appreciate your helps!