Oracle RAC and DataGuard configuration We have deployed an Oracle RAC cluster which consists of three Oracle instances. As we are considering the HA issue, and as far as I know, the only way of Oracle HA is DataGuard. So is it possible that we deploy DataGuard in another data center as backup for the master RAC cluster and if master RAC cluster down, We can switch the DataGuard to master which enable read and write operations. Someone told me that it is a very complicated process. Is that true? how much time does this process cost? Is there any other solutions on Oracle HA or any other load balance solution to replace RAC cluster? Does Mysql have the same capability?
(MySQL)

There are several MySQL Replication topologies.  For HA, deploying at least one server in each of 3 datacenters and using Galera Cluster, failover is essentially automatic if a datacenter goes down.  Some form of proxy or load balancer could take care of redirecting users to the still-alive nodes.  When the datacenter comes back up, that node will get back in sync.

If a node crashes and burns, wheel in a new server; the live nodes will pour a copy of the data set into it, and you are back on the air.

And you did not get paged.

(Now perhaps we will hear from users for which it was not that seemless.)

Group Replication is another HA product on top of MySQL.  I have seen 3 nodes being set up during a conference talk.  It took one person less than 5 minutes.

Caveat:  I cannot say whether either of these is easier or harder than Oracle's offering(s).