exercise-weather-service

Requirement and discussion

• The service can hard-code Melbourne as a city.

  I assume supporting multiple cities/locations is out of scope of this exercise.

  If query parameter city is not Melbourne, "unknown city" error will be returned.

  If multi-cities is required, we can implement with redis db, or use sync.Map, or use normal map as in-memory cache with RWMutex on map keys and RWMutex in each element of the map.

• The service should return a JSON payload with a unified response containing temperature in degrees Celsius and wind speed.

  I have found wind speed from these two sites are very different. Please check issues.md for details.

  When error, none OK status code will be returned, and playload like below will be returned.

  {
  	"error": "query parameter city is missing"
  }
  

• If one of the providers goes down, your service can quickly failover to a different provider without affecting your customers.

  For "quickly failover", configurable timeout has been implemented. config.json is an example config file.

• Have scalability and reliability in mind when designing the solution.

  • My solution is very easy to setup (one config file with default file name and default values). Docker or serverless could be used for scale out.
  • Many errors and corner cases have investigated and tested.
  • Request rate limit middle-ware could be implement and plug-in to improve reliability if required.

• Weather results are fine to be cached for up to 3 seconds on the server in normal behaviour to prevent hitting weather providers.

  For implementing this, http handler is created with an instance of cache, and the workflow is:

  • Get read lock for cache
  • Check if cache is younger than 3 seconds (inclusive), if yes return cache. Otherwise, next step
  • Release read lock
  • Get read/write lock
  • Query on external provider and refresh cache
  • Release read/write lock

• Cached results should be served if all weather providers are down.

  Additionally, if no cache has been created yet, and all providers are down, an error message json below will be returned.

  {
      "error": "error on getting weather from external"
  }
  

• The proposed solution should allow new developers to make changes to the code safely.

  To achieve this, I have been trying to:

  • Follow all SOLID principles, for example:
    • Dependency inversion principle has been used for designing failsafe provider in this solution.
    • The most of modules are assembled in main.go file by dependency injection technique.
  • Follow TDD process and the important modules have reached more than 90% coverage
  • Write "Clean Code"
  • Build a simple and easy development process.

Note

• Due to size and purpose of this project, compare with normal project I have skipped or been relexed for below:
  • For integration tests, my results are not verified automatically. I have been relied on unit test heavily in the project.
  • Docker container has been skipped, which normally could be used for scaling out or dev/test for micro services.
  • Web service frameworks has been skipped, which normally could be used for simplifying and standardize micro service implementation.
  • Popular libraries for logging and config file have been skipped.
  • Unit tests for some module have been skipped.
  • Access keys for external providers have been kept in github in example config file, which is bad pratice for security reason.

Build and test in Linux

In command line under the directory of this project, you can use command below for running unit test, build, integration test all together:

make

or run each step separately:

make utest # unit test
make build
make itest # integration test

You also can check build and test history in github actions tab in this project