Hardware requirements for Drupal 8 CMS and PostgreSQL DB.

Hi,

I will appreciate if someone can help me understand the Hardware requirements for Drupal 8 CMS and PostgreSQL DB. We will have 2 Drupal8 Instances in High Available Mode which will be behind Load Balancer to avoid Single Point of Failure and 2 PostgreSQL DB instances setup in Master-Slave Replication mode. 

Drupal 8 -> 2 VM Instances

PostgreSQL DB -> 2 VM Instances.

Any help will be highly appreciated and thanks in advance. 

Best Regards,

Kaushal