This server uses the Cluster API by default. You can update the amount of threads you would like. There is 8 by default. Ruby on Rails uses 5 by default. 8 threads is the most threads before having possible cross thread issues. Cross thread issues happen due to a poor API design that does not take into account unique identifiers and the possibility of gets or updates happening after a row is deleted. There are many cases of cross thread issues and with a proper API design you should be able to avoid these issues.
More Size is Required in your Deployed Environments
In AWS, you will need at least a t2.small to run your server with multithreads.