vehicle-aggregator-problem

Problem Statement

We have a city that runs its own buses & trains. They exposed their data via various microservices & some of these services are error-prone while some are reliable.

We need to build a reliable reactive aggregator service that aggregates all the data from dependent services (some of these are reactive & some are not. Refer to respective service & endpoints below for more info).

To achieve this, we need to

Implement all end points of following services

• Vehicle Aggregator Service
• Dependent 3rd party service (we need to build appropriate mock data such that all scenarios in Vehicle Aggregator Service can be tested)
  • Bus Metadata Service
  • Bus Live Fare & Location Service
  • Bus Fallback Fare Service
  • Train Live Location Service
• Write integration tests for all endpoints in Vehicle Aggregator Service.
• Follow best practices at all levels: Java, Spring (both in Reactive & non-Reactive world), Low level design, API error handling, Build & others.

Here are the responsibilities of each service

Service	Responsibility
Vehicle Aggregator Service	Generates & aggregates various data streams, handles & auto-recovers from upstream errors.
Bus Metadata Service	Stores Metadata related to buses.
Bus Live Fare & Location Service	Provides fast & accurate realtime fare of each bus amp; also provides a stream of all buses. But all endpoints in this service are not reliable i.e endpoints fail often.
Bus Fallback Fare Service	Provides outdated fare details for each bus. Reliable (doesnt fail often), Slow & Outdated older data.
Train Live Location Service	Provides realtime stream of all trains. Reliable, Fast & Accurate.

Here is the outline of endpoints we need to implement (implementation constraints for each of the endpoint are mentioned in respective service section).

Service	Endpoint	What its expected to
Vehicle Aggregator Service	GET /buses	Returns list of buses along with their fares, where fares are fetched from fallback service if fetching of this info from live service fails.
	GET /vehicle-location-stream	Exposes an infinite reliable stream that aggregates (1) Error-prone bus location stream (auto recovers i.e resubscribes incase of upstream errors out) with (2) Reliable train location stream.
Bus Metadata Service	GET /metadata	Fetches already stored metadata about all buses.
Bus Live Fare & Location Service	GET /buses/{id}/fare	Given a bus id, we need to fetch latest fare for the vehicle in question. Fails 50% of Time.
	GET /location-stream	Exposes a location stream that contains events representing movement of all buses in the fleet. Each event will have location information along with bus id. Unreliable stream that emits 1 event/second & stream fails after emitting 5 items.
Bus Fallback Fare Service	GET /buses/{id}/fare	Given a bus id, we need to fetch outdated older version fare for the vehicle in question.
Train Live Location service	GET /location-stream	Exposes a location stream that contains events representing movement of all trains. Each event will have location information along with train id. Reliable infinite stream which emits 1 event/second that never fails.