Requirement

Write an HTTP API that takes a temperature value in Celsius as input and gives the equivalent temperature in Fahrenheit as the output. The same API endpoint should also be able to take the temperature in Fahrenheit and output the equivalent temperature in Celsius.

Technical Design Thoughts

Sl No	Design Thoughts	Additional Note
1	The API should be easy to maintain
2	Avoid boiler plate code	Maximize the use of already tested open source libraries
3	The framework/technology should be 'code-wise' scalable	Should be easily able to change features on the go
4	Maintainable code with less over head
5	The existing backend implementation should not get too much affected when additional requirements comes in
6	Error handling should be automatically handled through framework(for majority scenarios)
7	The technology should well support existing HTTP clients
8	There should be a mechanism inbuilt in the framework to give only necessary details on every particular request
9	Framework should support asynchronous requests
10	It should have support for major database vendors and different kinds of databases
11	The developing service should be 100 % federated service	Federated service means, data and the associated application should be absolutely isolated from the rest of the system
12	The framework itself should have good support for Integration and Unit Testing
13	The framework should have support for a well known service discovery system(or for a better Backend for frontend layer-> BFF)
14	It should be way better if we can choose same end point to serve multiple request with out touching existing service
15	The framework + code should have light memory foot print and less prone to vulnerabilities
16	The framework should have inbuilt support for permission hooks	Authorization and authentication can be easily controlled through these hooks

What are the problems with traditional rest apis interfaces?

Sl No	Pain points	Additional Note
1	Less flexibility over leveraging existing service	Most of the times modification to existing interface is necessary
2	Joining data from two services to the front end will be additional over head
3	Custom error handling should be done separately
4	need additional effort for field masking

Points which has not been considered are as follows (It is not mentioned in the requirement)

Sl No	Points not considered
1	Data persistence
2	Request tracking
3	Authorization and authentication
4	Multi threading

By considering the above points and below are the technical design choices made.

Sl No	Tech stack used
1	Python
2	Strawberry graphql
3	pytemperature (python package for temperature conversion)
4	Server is configured to make all query and mutation request via HTTP Post
5	Fast API web server

Additional Points

Sl No	Additional Points
1	Python has been used to simplify the development
2	Strawberry graphql has been used because of its data first approach various benefits outlined in the above sections
3	pytemperature (python package for temperature conversion) better to avoid custom boiler plate code
4	Strawberry graphql can be easily integrated with apollo federation
5	Fast API web server is extremely fast when considering asynchronous application (netflix dispatch service is using fast api )

Functionality of the application

Sl No	Functionalities
1	Mutation for converting degree celsius to fahrenheit and vice versa
2	A query for application health check

1. Docker compose has been provided for local deployment

2. Code coverage has been made to 100%

Further reference

1. strawberry python

2. graphql core concepts

Local Build Deployment And Testing Information

Sl No	Purpose	Command
1	Build Image	docker compose build temperature-conversion-api
2	Run Tests	docker compose run temperature-conversion-api pytest --cov=api tests/ -v
3	Deploy application	docker compose up temperature-conversion-api
4	API EndPoint	http://localhost:8000/graphql
5	API docs and PlayGround URL	http://localhost:8000/graphql

Curl Script for calling the API Locally After Deployment

Degree Celsius to Fahrenheit Conversion

curl -g -X POST -H "Content-Type: application/json" -d '{"query":"mutation { convertTemperature(inputTemperature: 68569.22, unitToConvert: FAHRENHEIT) { unit, value, convertedAt } }"}' http://localhost:8000/graphql

Fahrenheit to Degree Celsius Conversion

curl -g -X POST -H "Content-Type: application/json" -d '{"query":"mutation { convertTemperature(inputTemperature: 123456.6, unitToConvert: DEGREE_CELSIUS) { unit, value, convertedAt } }"}' http://localhost:8000/graphql