ProxySQL in PXC and failing all nodes I'm going to install Percona XtraDB Cluster, and I have two questions about it:

1- Is it the last step?  https://www.percona.com/doc/percona-xtradb-cluster/LATEST/verify.html

Or installing ProxySQL is mandatory? I have only 3 nodes and not planning to add an extra node only for ProxySQL! And I think I don't even need it, my round-robin load-balancer is sending the requests to these servers randomly (without health controlling).

So if a node is down it can't even read/write to the DB.
in a nutshell, my application nodes are the same as my DB nodes, and a load-balancer in front of them, So I think I don't need ProxySQL, Am I?



2- What happens if all 3 nodes are down together, I think if this situation happens in a common Group Replication of MySQL, all the cluster collapses and all nodes are being removed from the cluster and we need to reconfigure the cluster manually again, Is the same problem exists in PXC or not?
No, installing ProxySQL is not mandatory 
Do you mean all three nodes close down suddenly rather than close down gracefully? What version of Percona XtraDB Cluster are you using? If it is a version 5.6.19 or later, then the nodes will read the last state on startup and will try to restore primary component once all the members again start to see each other. This makes the PXC cluster to automatically recover from being powered down without any manual intervention. This information came from https://www.percona.com/blog/2014/09/01/galera-replication-how-to-recover-a-pxc-cluster/ and you may find other useful blogs around this subject and/or webinars on the Percona site. 


Disclosure: I am from Percona