zkHelper

Zookeeper helper utility for leader election, observe node change, and configuration change etc.

For instance

• init() options:
  • basePath: 'myapps'
  • node: myhostname:123
• every apps in this leader election will restarted repeatedly using forever, nodemon and etc.

zookeeper nodes structure looks like:

  /myapps
        /nodes/myhostname:123
        /votes/n_00001

/myapps has the elected master.

{
    "master": "myhostname:123"
}

• When myapp calls init(), new node is create below /myapps/nodes. master node is elected using an voting ticket below /myapps/votes.

• On master change, every apps(including the master) participated in this leader election will restart. The master will not be changed when restarted within zookeeper sessionTimeout.

• Any connection failure to zookeeper leads process.exit()

  • A temporary disconnection is ignored one time and check again after 5 secs(one tick(2sec) * 2 + 1 sec)

init(options, callback)

• options * basePath: zk basePath, optional if observerOnly * node: host [':' + port], optional if observerOnly * servers: zookeeper servers * configPath: optional * noRestartOnConfigChange: optional, default false * logger: console(default) * clientOptions: zookeeper client options * observerOnly: false(default), true: no voting, read status change only
• callback: err, client(created zk client)

master election mode(default)

getMaster()

• returns current master.

isMaster()

• returns ture if current app is master

getConfig()

• returns configuration object
• configuration node path is provided via init options.configPath

Example

var zk = require('zkHelper'),
options = {
  basePath: '/myapps';
  configPath: '/myapps/config',
  node: require('os').hostname(),
  servers: ['zk0:2181', 'zk1:2181', 'zk2:2181'], // zk servers
  clientOptons: {
    sessionTimeout: 10000,
    retries: 3
  }
 };
 zk.init(options, function (err, zkClient) {
   var appConfiguration;
   if (zk.isMaster()) {
     console.info('i am master')
   } else {
     console.info('master', zk.getMaster() && zk.getMaster().master)
   }
   appConfiguration = zk.getConfig();
   // do something
 });

#observer mode

• init() with options.observerOnly : true
• Do not participate in leader election, and observe status changes only.
• data event is for master info. children event for node list changes.

event

on('data', path, newVal, oldValue)

• master change event
• newVal: master info, {master: node_name:port }
• oldValue: null if first time retrieval.

on('children', path, newVal, diff)

• children change event
• newVal: node list
• diff.added: added node list
• diff.deleted: added node list
• use _.debounce to get settle downed node list.

Example

var zk = require('zkHelper'),
_ = require('lodash'),
options = {
  servers: ['zk0:2181', 'zk1:2181', 'zk2:2181'], // zk servers
  clientOptons: {
    sessionTimeout: 10000,
    retries: 3
  },
  observerOnly: true
 };
zk.init(options, function (err, zkClient) {
  var observer = new Observer('/otherApp');

  observer.on('children', _.debounce(function (path, newVal, diff) {
    consol.info('Master=%j', observer.getMaster());
    logger.info('[%s] children:[%s] added=[%s] deleted=[%s]', path, newVal, diff.added, diff.deleted);
  }, 500));
  observer.on('data', function (path, newVal, oldVal) {
    if (oldVal) {
      logger.info('master change:' + path);
    }
    logger.info('Master=%j', observer.getMaster());
    logger.info('[%s] data: %j <- %j', path, newVal, oldVal);
  });
});

License

(The MIT License)

Copyright (c) 2013 Daliworks Inc

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.