Support for sharded databases and replicas for ActiveRecord

ActiveRecord Shards is an extension for ActiveRecord that provides support for sharded database and replicas. Basically it is just a nice way to switch between database connections. We've made the implementation very small, and have tried not to reinvent any wheels already present in ActiveRecord.ActiveRecord Shards has been used and tested on Rails 5.x and 6.0, and has in some form or another been used in production on large Rails apps for several years.