Worker implementation

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Package structure

[net]
    |_ [aftership]
            |
            |_  [config]
            |_______   beanstalk.config
            |_______   persistence.config
            |_  [handler]
            |_______   exchange_rate_job_handler.js
            |_  [persistence]
            |_______   database_manager.js
            |_______   [impl]
                            |_____ mongoose_db_manager.js
            |_  [tests]
            |_  [worker]
            |_______   exchange_rate_converter.js
            |_  [ws]
            |_______   exchange_rate_service.js
            |_______   [handler]
                            |_____ exchange_rate_response_handler.js

config - worker configuration files

handler - fivebeans worker handler implementation

persistence - database communication implementations

worker - fivebeans worker implementation

ws - Exchange rate web service implementation

ws/handler - web service response handler

Dependencies

The following dependencies are required:

• co
• bluebird
• fivebeans
• accounting
• mongoose

Job payload

{
    from: 'USD',
    to: 'HKD',
	succeeded_attempts: 0,
	failed_attempts: 0
}

The succeeded_attempts and failed_attempts properties are used to persist the attempts counter values when working in a distributed environment.

Different workers can process the same job but the success and fail counters should not be reset.

Currency Exchange API

The API used to get the currency is the one provided by https://currencylayer.com/ . The request must include a unique key provided after signing up. The response comes in JSON form. The free service only allows getting exchange rates from USD to an array of others among which HKD.

Note: a secondary API key is included in the exchange_rate_service.js file if the 1000 monthly request limit is reached.

Installation

Run the following command to install dependencies.

npm install

Note

The worker should be executed using the --harmony command line parameter because of the use of generators in the source code:

node --harmony start_worker_cluster.js.js

Run workers

Run single worker

node --harmony start_worker.js

#####Run as cluster

node --harmony start_worker_cluster.js [number of workers]

If the [number of workers] parameter is not specified the number of workers to be initialized will be the number of processors available on the machine.

The challenge

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• DOWNLOAD this repository to your own Github public repository.
• Create a new repo, name it by using this shortGUID generator
• Do NOT fork, as other candidates would be able to see your solution easily.
• Use beanstalkd, mongodb, nodejs
• Get the xe.com exchange rate, store it in mongodb for every 1 min.

Goal

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Code a currency exchagne rate worker

1. Input currency from USD, to HKD
2. Get USD to HKD currency every 1 min, save 10 successful result to mongodb.
3. If any problem during the get rate attempt, retry it delay with 3s
4. If failed more than 3 times, give up the job.

Requirements

• Scale horizontally (can run in more than 1 process in many different machines)
• Using co + bluebird

FAQ

• consumer worker is the script to take the job from the queue, in this case is the scraper to get the exchange rate.
• seed is the first data input, say HKD to USD to the queue.
• producer worker is used to SEED the data only, it is optional in this challenge.
• If you don't have xe.com api key, use your own way to get the answer.

How it work?

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1. Seed your job in beanstalkd, tube_name = your_github_username

Sample beanstalk payload for getting HKD to USD currency, you can use any format or modify the payload to fit your need.

{
  "from": "HKD",
  "to": "USD"
}

2. Code a nodejs worker, get the job from beanstalkd, get the data from xe.com and save it to mongodb. Exchange rate need to be round off to 2 decmicals in STRING type.

   a. If request is failed, reput to the tube and delay with 3s.

   b. If request is succeed, reput to the tube and delay with 60s.

mongodb data:

{
	"from": "HKD",
	"to": "USD",
	"created_at": new Date(1347772624825),
	"rate": "0.13"
}

3. Stop the task if you tried 10 succeed attempts or 3 failed attempts.

4. Scale horizontally: NOTICE that the above bs payload is just an example, you should make sure your script can be run as distributed system (in multiple instances / servers. Using CLUSER mode in NODE.JS DO NOT help)

5. You are coding the consumer worker, NEVER use your consumer worker to SEED the data.

6. You can seed the data to the tube with bs console or coding another producer worker to SEED the data.

Tools you need

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1. beanstalkd server is setup for you already, make a JSON request to this:

   /POST http://challenge.aftership.net:9578/v1/beanstalkd

   header: aftership-api-key: a6403a2b-af21-47c5-aab5-a2420d20bbec

2. Get a free mongodb server at mongolab

3. You may also need Beanstalk console or any tools u like.

4. MUST follow coding guideline

5. MUST follow coding documentation

Help?

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