zk-beacon

zk-beacon is a zookeeper announcement library designed to be used for service discovery. At it's core it uses ephemeral connections to zookeeper to insert a payload under the path defined in the configuration, and then just maintains this connection indefinitely, recovering from disconnections and session expiration as necessary to... keep the beacon lit. It is built on top of node-zookeeper-client.

This enables operation as a service discovery beacon by using an address and a port as the payload, and registering the path as the service identifier. It exports 2 main types, ZookeeperBeacon a class describing the beacon itself, and ZookeeperBeaconOptions, an interface which describes the configuration to pass to the ZookeeperBeacon constructor.

ZookeeperBeaconOptions has 3 required properties, servers which takes a string or list of strings that can resolve to a zookeeper server as described in the connection string documentation of node-zookeeper-client, path which describes the parent path which the announcement will be created under, and payload which describes the contents that will be added to the node under the path. A fourth, optional parameter, spinDelay, is used to determine the rate at which the beacon will try to reconnect to zookeeper.

ZookeeperBeacon is also an EventEmitter and will emit a handful of events described by BeaconEvents which is also exported by this library.

CONNECTED: "connected",
DISCONNECTED: "disconnected",
EXPIRED: "expired",
CREATED: "created",
ERROR: "error"

example

import { ZookeeperBeacon, BeaconEvents } from 'zk-beacon';
 
const serviceBeacon = new ZookeeperBeacon({
    servers: 'localhost:2181/discovery',
    path: `/myserviceidentifier`,
    payload: {
        address: 'localhost',
        port: 8080
    }
});
 
serviceBeacon.on(BeaconEvents.CONNECTED, () => {
    console.log('beacon connected');
});

Development

npm run build to compile.

The ZookeeperBeacon test currently require a local installation of zookeeper to run successfully, specified by the zkServerCommandPath variable which is defined near the beginning of the tests.