[Horizontal Scaling] How to synchronize multiple MySql managed clusters

Hello,

TL;DR How do i synchronize 2 mysql managed clusters that have 1 master and 5 slaves each?

I am currently planning to deploy my web application in digital ocean and am planning to use mysql managed database cluster to host my data. Relatively big traffic is expected in the not-so-distant future and thus I am planning to horizontally scale using master-slave replicas. While reading the docs i saw that a given mysql cluster can have up to 5 read-only nodes and that an account can have up to 10 clusters.

So, once the load is too big and writes to the database are quite often, a second master node will be needed, creating two clusters, with one master each and 1-5 slaves. How can i keep the data consistent between the two clusters so that users don’t lose their data?