DB max connection limits for Rails app and Postgres, Redis, Puma settings

Configuring the database connections pool for the Rails app might not be a straightforward task for many programmers. There is a constraint of max opened connections on a database level. Your server environment configuration can change in time and affect the number of connections to the database required. For instance number of servers you use can change when you autoscale it based on the web traffic. It means that the number of web processes/threads running for Puma or Unicorn servers could change. All this adds additional complexity. When you use two databases (e.g. Postgres Redis), everything gets more complex. In this article, we will address that. You will learn how to estimate needed database connections for your Ruby on Rails production application.