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A Simple Rules Engine

For one of my project, I needed a simple rules engine.

I like the DecisionDag that Mandar Jog built. It uses Commons JEXL and allows rules to be defined in plain english.

In my use case, I had following goals.

  • keep it simple (KISS)
  • rules engine as micro-service (deployable to cloud).
  • a rules catalog of sorts that allowed new versions of the rules to be added and older ones removed.
  • ability to calculate within the rule and return results.

This is a simple rules engine built with spring-boot in java.

The rules are in plain javascript.

Nashorn sccript engine allows runtime loading and evaluation of rules.

Instructions

  • Install the app by cloning the repository rulesengine

  • Build and run the app

       $ cd rulesengine
   $ gradlew bootRun

  • Call rest end-points.

       $ curl -v 'http://localhost:8080/api/rules/WhatToDo?family_visiting=yes'
   
   $ curl 'http://localhost:8080/api/rules/WhatToDo?family_visiting=no&money=poor&weather=good'
   
   $ curl 'http://localhost:8080/api/rules/WhatToDo?family_visiting=no&money=poor&weather=cold'
   
   $ curl 'http://localhost:8080/api/rules/WhatToDo?family_visiting=no&money=rich&weather=cold'

Cloud

Meet PCF Dev. It is a simplifed, and minimized version of the Pivotal Cloud Foundry intended for your local machine. And Getting started is simple.

#####Deploy to cloud

  • Target the cloud instance

       $ cf login -a api.local.pcfdev.io --skip-ssl-validation

   API endpoint:  api.local.pcfdev.io   
   Email>     admin
   Password>  admin

  • Build and deploy to cloud

       $ cd rulesengine
   $ ./gradlew assemble
   $ cf push -f manifest.xml

  • Test the cloud service

       $ curl -v 'http://simplerules.local.pcfdev.io/api/rules/WhatToDo?family_visiting=yes'
   
   $ curl 'http://simplerules.local.pcfdev.io/api/rules/WhatToDo?family_visiting=no&money=poor&weather=good'
   
   $ curl 'http://simplerules.local.pcfdev.io/api/rules/WhatToDo?family_visiting=no&money=poor&weather=cold'
   
   $ curl 'http://simplerules.local.pcfdev.io/api/rules/WhatToDo?family_visiting=no&money=rich&weather=cold'