pandwoter / emails_api

Backend Developer Take-Home Technical Challenge

- Description of the problem and solution.

Problem: email campaigns delivery (proxy) service. Implemented backend for UI from task technical description. Service handles calls to external Mail delivery providers in background worker.

- How to run the solution locally (no need to set up a live server or infrastructure).

This API is deployed - here Also here is Postman with predefined endpoints

git clone https://github.com/pandwoter/emails_api
cd emails_api
bundle 
bundle exec rails s

- Reasoning behind your technical choices, including architectural.

There is a simple provider rotation algorithm delivery/email_delivery_service.rb (we try to call each available provider sequentially, if we fail, we just go to another one). To scale horizontally with new providers we simply need to follow some conventions: 1) add mailers/providers/<provider_name>/base_mailer.rb which defines delivery_method and error interceptor for a particular adapter library 2) add provider name in ENABLED_PROVIDERS in delivery/email_delivery_service.rb (this constant is added for convenience (in case we don't want to include all providers from mailers folder in rotation)). Also, there is no business logic in controllers (I used services to encapsulate it). Each service returns Result monad (this is huge advantage for future tests). Also, I used dependencies injection in service constructors to achieve painless testing in isolation

- Trade-offs you might have made, anything you left out, or what you might do differently if you were to spend additional time on the project.

Actually we can tune up rotation algorithm to handle each request to a particular provider in thread (we can consider thread pool implementation) or asynchronously (async-http or any actor pattern implementation). Also, I had some problems with Mail providers API (because I haven't any own domain nor time to properly test and dive into possible Mail services drawbacks (I used sandbox domains, but some of the providers (such as AWS) have limitations like to send emails only to authorized accounts)). As an improvement we can store all delivery attempts and results in a separate table (for now we just keep this in delivery_state field of the campaigns table and schedule retry if all services in rotation pool are down). Also, we should add test coverage (it will be pretty simple with code organized in way as it is). Consider adding Docker/Composer config for painless local setup. Also, we can add Travis or any other CI tool for test executing.