Multi node install of zextras carbonio

Hello,

We want to deploy a multi-node carbonio in production for thousands of accounts. We want to redundant the various instances that make up our architecture. two ldap, two proxy, two mtna, two mailbox ...
We want to dedicate one or two instances to the postgresql database. My question is, what's the impact of having two postgresql instances in this multi-node installation, and if that's not feasible, how should we install the database to avoid interruptions?
Please help us, it's urgent