You are using Rails and want to setup distributed database reads.
Many older articles online recommend the use of the Octopus project for distributing database queries with Rails. However we no longer recommend the use of Octopus for this purpose. Despite the fact that there has been some activity on the repo, the maintainer claims that the project is not going to maintained, meaning that there may be better options elsewhere.
If you are using ActiveRecord then you may want to consider Zendesk's solution instead. Configuration is very straightforward and covered in the README on the project.