Test Assignment

This application's purpose is to: having a list of numbers and an arbitrary number called target, find two numbers (and their indexes), which sum will be equal to target.

This application consists of 2 services.

target-finder

The target-finder is responsible for finding those 2 numbers and their indexes. It needs an array of numbers and the target to find those numbers.

You can query this service like so:

curl -X POST 'http://localhost:8080/target' -H 'Content-Type: application/json' --data '{ "data": [ 1, 2, 3, -4 ], "target": -2 }'

Both data and target must be present.

This service can handle a few faulty scenarios:

• It can handle cases when the data does not contain a pair of appropriate numbers (the second service sometimes can yield a default target, which will not always satisfy all conditions).

{
    "CouldNotFindAppropriateValues": {}
}

• It handles cases when there is not enough data because there must be at least 2 numbers.

{
    "NotEnoughData": {}
}

The error code will be 400 is such cases.

When you try to access a resource, which does not exist you will get 404.

target-router

This service is responsible for fetching target from https://httpbin.org and forwarding it to target-finder. It follows similar patter as target-finder, it accepts the object (however, this time target is optional), but uses a different endpoint and port. Besides, it is rate limited.

You can query this service like so:

curl -X POST 'http://localhost:4040/find' -H 'Content-Type: application/json' --data '{ "data": [ 1, 2, 3, -4 ], "target": -2 }'

You can exclude target. In this case, it will be fetched from https://httpbin.org/get. In case you provide target, it will use https://httpbin.org/get?target=[target]. In case it encounters any error, it will use the default value, which can be configured via an env called TARGET.

This service forwards all request to target-finder and preserves the response, meaning you may encounter errors specified for target-finder.

This endpoint is rate limited. It uses a token bucket rate limiter to achieve it. You need to specify the number of tokens via TOKENS env and the number of requests per minute via REQUESTS env. Each time the client makes a request, it will need to have at least one available token. Otherwise, the request will be rate limited and rejected. The tokens get recovered in such a rate that you will be able to make REQUESTS per minute. This token behavior allows to handle bursts of request gracefully.

Each request will be enriched with X-Rate-Limit-Limit, X-Rate-Limit-Remaining and X-Rate-Limit-Reset. X-Rate-Limit-Limit is the maximum number of tokens, X-Rate-Limit-Remaining is their remaining number, and X-Rate-Limit-Reset is a timestamp when all used tokens (X-Rate-Limit-Limit - X-Rate-Limit-Remaining) will be recovered if no one uses the API. You can view logs to monitor the recovery of the tokens. You can

Besides, you can disable target-finder with DEBUG_RATE_LIMITS to test these headers. With this env enabled all requests will be automatically rate limited.

Deployment

To build Docker images locally, run:

sbt docker:publishLocal

After this, 2 Docker images will be created, target-finder and target-router. Then, you will simply need to run:

docker-compose up

You may want to look into the docker-compose.yaml to check and modify envs.

Technology stack

ZIO, ZIO-HTTP, Circe

Possible Improvements

• The rate limiter must be implemented as middleware.