existence-cache v1.0.2

existence-cache

An NPM package that uses either ElastiCache or local memory to set and check for the existence of keys

Installation

npm install existence-cache

Usage

You set up configuration when requiring the module.

The parameters it accepts being: (elasticache_endpoint, elasticache_port, horribleErrorFunc), where:

• elasticache_endpoint (Optional) - Endpoint for a Redis-based ElastiCache cluster
• elasticache_port (Optional) - Port for the cluster, defaults to 6379
• horribleErrorFunc (Optional) - Function to call if it cannot connect to the cache (ElastiCache or in local memory)
  • Will run horribleErrorFunc(message, error) upon a horrible error if a function is provided.

If elasticache_endpoint is not specified, this will default to caching using local memory.

Require it like this:

var cache = require('existence-cache')('somecluster.abcde.0001.usw2.cache.amazonaws.com', 6000, postSNSAlert);

or just like:

var cache = require('existence-cache');

Then, use it like this:

cache.set("key", 20);
cache.check("key");

Where cache.set behaves as a synchronous function and its parameters are

• key - A unique string
• ttl - (Optional) Time to live, in seconds.
  • 0 will permanently set the key, negative values will delete it.

  • Defaults to permanently setting the key.

And cache.check behaves as an asynchronous function and has the parameter:

• key - A unique string to check if it exists (has been set in the cache and not expired)

Example

var cache = require('existence-cache')(null, null, console.error);
cache.check("15")
    .then(function(){
        console.log("Setting the key in the cache.");
        return Promise.resolve(cache.set("15", 1));
    })
    .then(function(){
        console.log("Made it here!");
        return Promise.resolve(cache.check("15"));
    })
    .then(function(){
        console.log("This code doesn't run, since 15 was in the cache.");
    })
    .catch(console.log);

###Some Notes about ElastiCache The ElastiCache functionality only works with Redis-based ElastiCache Clusters.

ElastiCache is only accessible from an EC2 instance (whether you start that instance directly, or through Elastic Beanstalk).

When setting up your clusters, be sure they are in the same VPC as your EC2 instance(s) and that the security group has the appropriate inbound rule to allow access to ElastiCache.

For further reference, see Amazon's documentation.