omen

Omen is a distributed host process coordinator

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Omen

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Omen is a distributed data system, running within your load-balanced Node.js service. It has redundant caching and storage, with hash ring orchestration, eventual consistency and latency-optimized routing.

Advantages

  • Omen is part of your application. It frees you from installing, configuring and connecting to multiple data services.

  • Omen uses the very stable and fast LevelDB database via the leveldown module for disk persistence.

  • Modern web services have features such as load balancing, multi-region deployment, process management, monitoring, auto scaling, continuous integration and more. Omen is part of your service, so it gets your service's operational features for free.

  • Omen is crazy fast, because:

    • Peers measure latency and use the fastest routes.
    • One ring handles caching and storage, so network requests are reduced.
    • In-process objects can be modified without deserialization.
    • Requests can route internally because clients can also be peers.
    • Frequently-written data can be pre-aggregated locally.
    • Frequently-accessed data can be cached globally.

Install Omen

npm install --save omen

Use Omen

var server = require('za')().listen(8888);

var ring = require('omen')({
  hostPattern: 'app-(eu|use|usw|apn)-(1-5).lighter.io'
});

ring.set('foo', 'bar', function (err) {
  ring.get('foo', function (foo) {
    process.assert(foo == 'bar');
  });
});

omen([options])

The omen library outputs a ring object on which ring methods are called. A ring object is created with several options that govern the ring's bootstrapping and behavior.

options.processCount

The process count specifies the number of CPUs per host, and it defaults to using all available CPUs.

options.dataLocation

The database path is where LevelDB data is stored, with a subdirectory for each worker. The default path is the data directory in the current working directory.

options.replicas

The replicas setting indicates the number of times to replicate a key-value pair around the ring for redundancy. This number includes the main entry as well as duplicates, so it must be at least 1, and the default is 5.

options.cacheSize

The cache size indicates the number of items to keep in LRU cache, with the default being 10,000.

options.basePort

The base port is the first port on which processes will listen, with each subsequent process incrementing that number by 1. The default is 12300. So if a host has 4 processes and uses the default basePort, it will listen on ports 12300, 12301, 12302 and 12303.

options.hostPattern

The host pattern is used to bootstrap the host discovery process. It defaults to the current hostname, so it must be set in order to allow multiple hosts to interact.

The pattern supports parenthetical expressions which can be pipe-delimited lists or a start and end number for a sequence. So if you had 10 hosts across 2 US locales, your host pattern might look like: "omen-us(east|west)-(1-5).domain.tld".

options.isClientOnly (Default: false)

If the current process needs to access the ring, but will not store data as a peer, it should set isClientOnly to true. The default is false.

options.pingDelay (Default: 1e3)

The ping delay is the number of milliseconds a peer waits between attempts to discover all peers or heartbeats to a peer to verify the connection and to measure latency. The default is 1,000 (one second).

options.log

Omen can use a custom log. The default is console.

ring

ring.increment(key[, path, number, fn])

ring.on()

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