Fig. 1.

Rayyan architecture. Rayyan is a fully cloud-based architecture that uses a cloud platform as a service allowing elastic scaling of resources as we get more users and more requests. Rayyan’s workers are distributed using the load balancer to different app servers (Ruby web workers). These workers are elastic; they auto-scale based on traffic to guarantee minimal response time. For longer jobs or the elastic delayed jobs (the worker bees), such as upload parsing, similarity computation, and label predictions, they are handled through a queuing system. All workers have access to the storage layers: Postgres (for permanent storage), Solr (for indexing and searching), and Memcached (for caching results). Other parts of Rayyan, written in Java, are attachable to the jobs using an Apache Thrift service. Real-time notifications, on job completion or chat messages, for example, are delivered using Pusher, while other transactional information are delivered using the Mailchimp Mandrill service. All system activities are logged by Logentries and later backed up on AWS S3, while live instrumentation and monitoring is done by NewRelic