Telegraft

Telegraft is a university project whose goal is study the Raft consensus algorithm: it is a simple distributed and replicated chat application which supports the Raft protocol. Telegraft uses Scala and relies heavily on Akka's technologies.

Architecture

Since it is a distributed application there are many Telegraft nodes, each one is composed of 2 services:

• telegraft-raft-service which is the Raft implementation
• telegraft-statemachine-service which is where the actual business logic happens, the state machine receives read and write requests from telegraft-raft-service and queries a database in order to provide an answer.

telegraft-benchmark-service is a project based on Gatling, and its purpose is to provide a meaningful benchmark and stress test for Telegraft. Follows a diagram which shows the interactions between the components at runtime:

How to improve this project

Session and authentication

These are arguably the most important missing features. Both were not even investigated for lack of time.

Generation of IDs

IDs in the database are auto-incremented integers, this solution is "good enough" in a small POC, it works because the database itself is only replicated, not sharded: thus all replicas receive the same write queries. The reason of using integer auto-generated primary keys is that state should be consistent between all replicas: using any other method would have required setting up a custom way of generating and delivering to replicas unique primary keys.

Of course the current solution is not good in a real-world scenario, where usually the database is sharded and there are many concurrent writes, many clusters each of them using some kind of consensus protocol. A solution was provided by Twitter with Snowflake, the project is now archived but there are many updated forks.

Using streams

Both the telegraft-raft-service and the telegraft-statemachine-service modules could benefit from using streaming RPCs. A streaming oriented gRPC service supports back-pressure. This could be useful both for communications between clients and the raft cluster but also between any raft server and its respective state machine.

More documentation

Further information on the single projects is contained in their READMEs:

• telegraft-raft-service
• telegraft-statemachine-service
• telegraft-benchmark-service.