service-patterns.md

Service Patterns

Metaparticle simplifies distributed systems by enabling users to define their services in terms of canonical service patterns. Metaparticle then handles the details of transforming those services into concrete instatiations.

The currently supported service patterns are:

Simple Service

A simple service simply exposes a function as an HTTP service.

Example:

// Create a simple service.
var service = mp.service(
    "simple-service",
    // @param {Object} request is an in-bound JSON body from a POST
    // returns {Object} serialized to HTTP and sent back as the response
    function(request) {
        return {"theRequest": request};
    }
);

Scatter/Gather

A Scatter/Gather service fans all requests out to all leaf nodes (scatter phase), all responses are then aggregated in a root node (gather phase), this aggregate response is returned to the caller.

Example:

var service = mp.scatter(numLeafInstances, leafFunction, mergeFunction);

See histogram.js for a complete example.

Shard

A Shard service runs a user specified function to select a shard (replica) for a request, the request is then forwarded on to this specific replica, and the response from that replica is returned to the caller.

Example:

var service = mp.shard(numShards, shardingFunction, leafFunction);

Spread

A Spread service is similar to a Shard service (in fact they use the same underlying implementation) but the Spread service uses a randomized shardingFunction so that each request is routed to a random replica and load is uniformly spread between replicas.

var service = mp.spread(numReplicas, leafFunction);