hakyer/email-service repository overview

⁠Email Service coding challenge

Email Service accepts the neccessary information and sends messages. It provides an abstraction between the following email service providers:

• SendGrid⁠
• Mailgun⁠

It implements fail-over - if one of the providers goes down, Email Service quickly fail-overs to a different provider without affecting customers. If some provider keeps failing it marks the provider as down and temporarily avoid using it.

⁠Running

First edit the config file config.yaml⁠ and specify api keys.

⁠Docker

docker run --name email-service -v <absolute path to config.yaml>:/app/config.yaml hakyer/email-service:latest
docker exec -it email-service /bin/bash

⁠Developer machine

go run main.go

⁠Verify server is working

curl http://localhost:9091

⁠Send an email message

POST /messages

curl -u admin:password -F from="[email protected]" -F to="[email protected]" -F subject="Subject" -F text="Text" http://localhost:9091/messages

⁠Notes

• Software development process used
  • Test-driven development
• Architecture
  • hexagonal
    • app⁠ package contains domain logic and is independent of any external library, provider or framework
    • infra⁠ package contains all technical stuff
      • rest⁠ is for exporting domain as a REST server
      • providers⁠ contains piece of code integrating with external email providers
      • metrics⁠ counts Prometheus emailservice_send_messages_total metric
      • config/yaml⁠ loads config from config.yaml

⁠Tests

• unit tests
• acceptance test
  • acceptance-tests⁠ contains component tests veryfing if whole domain logic works as expected (useful for non-technical people)
• integration tests
  • integration-tests/providers⁠ have integration tests verifying if real messages are sent

⁠Technology stack selected

• programming language - Golang
• unit tests - Testify
• acceptance tests - Godog
• integration tests
  • Mailslurp for testing code with real emails
  • Resty for making HTTP calls (official library from Mailslurp does not even compile)
• email providers clients - official ones
• logging - Logrus
• containerization - Docker
• My experience with Golang - 7 months

⁠How to extend

⁠Adding a new email provider

• Implement EmailProviderFactory
• For integration testing inbox⁠ can be used to verify if real messages are being sent
• Add it to infra/email_service_factory.go⁠
• Add configuration to config.yaml⁠

⁠Missng features

• HTTP over SSL
• Email Message parameters validation

⁠Scalability

• Service is stateless therefore it can be easily scaled by adding new instances
  • there is no state (database), no distributed locks etc