Configuration Library

Configuration Library for nodejs client applications.

Project Description

1. The library initialization should expect a customer-key that we provide to our customers.
2. The library needs to expose a method that returns a single value based on a key.
3. The library should get the configuration from our servers.
4. The library should save (cache) the configuration for future launches in order to reduce the init time.
5. Every time the library is initialized, it should get the configuration file from the server (since it might have been updated)
6. The library should not block the execution of the app/service while getting the configuration from the server.
7. The library should expose a way to get a default value. In case there is no locally cached configuration (e.g. first time ever, the app/service starts), and the customer code requests a value for a key before the response from the servers arrived.
8. A real scenario is for the configuration to be used for feature toggling. Product managers might use this configurations to toggle on/off features in the code. Like all new things, a new feature can have problems and we need to be able to control these changes. For example, the app might run without any problem for a long time. Then someone turns “on” a new feature. This feature crash the process. In the case that the process crashes, we will want to disable (turn “off”) the feature and stop the app from crashing. Since we said that the library needs to get the configuration from the configuration server in async way, the process might load a cached configuration that will cause the crash before the it gets the updated response with the disable instruction from the server. Every time the app/process will starts, it will crash again. Because of that, the the library needs to be smart and detect that the previous process crashed. If it did, the library will prevent the crash of process while getting a configuration from the server (which hopefully fixes the crash).

Prerequisites

• NodeJS v6.9+

Setup Environment

• Please run npm install to install all dependencies.

Run Tests

• All tests are under ./spec/**/*.spec.js, please review it for better understanding of the library functionality.
• use 'npm test' to run the library test

Class Methods

• function init(props);

  • Library initialization
  • Properties:
    • key: customer key that used by the server for authentication
    • cacheFile: cached configuration path
    • crashFile: crash logfile path, this file is used by the library in order to do a different initialization flow in case of previous crash
    • server.domain: configuration server domain
    • server.apiPath: The REST api path to get and post the configuration

• function get(key, defaultValue);

  • Returns the value for a key
  • Parameters:
    • key: The key
    • defaultValue: The default value in case the key is missing for some reason

• function getProperties();

  • Returns the library properties