Chats app

Setup

1- Start the services.

docker-compose up

2- Create the databases.

docker-compose exec rails_app bundle exec rake db:create

3- Run the migrations.

docker-compose exec rails_app bundle exec rake db:migrate

4- Create elasticsearch index.

docker-compose exec rails_app bundle exec rake searchkick:reindex:all

5 - Run rspec

docker-compose exec rails_app bundle exec rspec

API

Endpoints for rails_app, serving at localhost:3000

verb	route	body params
GET	/apps
POST	/apps	name
GET	/apps/:token
PUT	/apps/:token	name
GET	/apps/:app_token/chats
GET	/apps/:app_token/chats/:number
GET	/apps/:app_token/chats/:number/search?q=:search_string
GET	/apps/:app_token/chats/:chat_number/messages
GET	/apps/:app_token/chats/:chat_number/messages/:number

---

Endpoints for go_app, serving at localhost:8000

verb	route	body params
POST	/apps/:app_token/chats
POST	/apps/:app_token/chats/:chat_number/messages	body

---

Design

Chats and messages creation

• In go_app redis handles the chat/message number using Incr command, then go_workers2 pushes a job to sidekiq to create a chat/message and a response is sent to the user with the number.

• Sidekiq is then responsible for creating the chat/message, incrementing the chats_count/messages_count and presisting the data to mysql.

• A message queue (RabbitMq, kafka, ...etc) could've been used, but since redis is a single point of failure in this design, introduceing another single point of failure is not optimal, specially since the same functionality can be achieved using redis.

• For this to work I used go_workers2 pacakge, which can publish jobs to sidekiq, in this way redis is used as both:

  • Generator for chat/message numbers, since redis is single threaded it's ACID complient by nature, hence we can guarantee that there will be no race conitions in chat/message numbers creation.
  • Communication queue between the 2 services to push jobs from go_app to sidekiq.

• Database locks are used to ensure that the chats/messages_count are correct, and transactions are used to make the 2 operations (creating the chat/message and updating the count) atomic.