Hello, @geraldmaricau

I believe you will find this helpful:

DigitalOcean Managed Databases offers three types of nodes:

The primary node of a database cluster processes queries, updates the database, returns results to clients, and acts as the single source of data for all other nodes.

Standby nodes are copies of the primary node that automatically take over if the primary node fails. Database clusters may have zero, one, or two standby nodes.

Read-only nodes are copies of the primary node that process queries and return results but cannot make changes to the database itself. They provide geographically distinct, horizontal read scaling.

A database cluster is comprised of one primary node and its standby nodes. Read-only nodes are not considered part of the cluster.

https://www.digitalocean.com/docs/databases/

Let me know if something is still unclear

No i think it’s a little bit more clear for me but i have another question more about the existence at the same time in one cluster.

One cluster configuration cannot be used for several differents engines ?
To be clear also about the creation we pay for one cluster or for the number of nodes inside a cluster.

And if i understood very well one cluster integrate several nodes of the same engine (MySQL, PostgreSQL or Redis: 3*). Or could we have MySQL in one node of a cluster and in the same cluster one node of PostgreSQL for example.

What is the maximum number of nodes inside a cluster ?
Is it 2 : several primary (for each engines types : 3) and several standby (with different or the same engines : 3).

Thanks.