zookeeper

Overview

node-zookeeper - A Node.js client for Apache Zookeeper.

This module is implemented on top of the ZooKeeper C API; consult the ZK Reference for further details on behavior.

Latest changes are described in the changelog

Installation

(note the name zookeeper in lowercase)

npm install zookeeper

Examples

Use the async/await enabled client:

const ZooKeeper = require('zookeeper').Promise;

Note: checkout the API for the async/await enabled client here

There is also a callbacks based client:

const ZooKeeper = require('zookeeper');

Note: checkout the API for the callback based client here

Example: create a client

Create an instance of the ZooKeeper client using async/await:

function createClient(timeoutMs = 5000) {
    const config = {
        connect: host,
        timeout: timeoutMs,
        debug_level: ZooKeeper.ZOO_LOG_LEVEL_WARN,
        host_order_deterministic: false,
    };

    return new ZooKeeper(config);
}

const client = createClient();

The client is ready when connected to a ZooKeeper server:

client.on('connect', () => {
    // start using the client
});

client.init(config);

Example: create a node

Using the API of the async/await enabled client.

const path = '/myPath';
try {
    const createdPath = await client.create(path, data, ZooKeeper.ZOO_EPHEMERAL);
    console.log(`(created: ${createdPath})`);
} catch (error) {
    console.log(`${path} already exists`);
}

More examples

Check out the code in the examples folder: master,workers, tasks and listeners scenarios.

API Reference

Methods: async/await enabled client

• init(options)
• connect(options, connect_cb)
• close()
• path = await create(path, data, flags)
• mkdirp(path, callback(Error))
• stat = await exists(path, watch)
• data = await get(path, watch)
• children = await get_children(path, watch)
• [children, stat] = await get_children2( path, watch)
  • return value types:
    • children is an array of strings
    • stat is an object
• stat = await set(path, data, version)
• val = await sync(path)
• delete_ (path, version)
  • (note the trailing _)
• set_acl(path, version, acl)
• acl = await get_acl(path)
• add_auth(scheme, auth)

The watcher methods are forward-looking subscriptions that can recieve multiple callbacks whenever a matching event occurs.

• stat = await w_exists(path, watch_cb)
• data = await w_get(path, watch_cb)
• children = await w_get_children(path, watch_cb)
• [children, stat] = await w_get_children2 (path, watch_cb)
  • return value types:
    • children is an array of strings
    • stat is an object

Methods: callbacks based client

• init(options)
• connect(options, connect_cb)
• close()
• a_create(path, data, flags, path_cb)
• mkdirp(path, callback(Error))
• a_exists(path, watch, stat_cb)
• a_get(path, watch, data_cb)
• a_get_children(path, watch, child_cb)
• a_get_children2(path, watch, child2_cb)
• a_set(path, data, version, stat_cb)
• a_sync(path, value_cb)
• a_delete_ (path, version, void_cb)
  • (note the trailing _)
• a_set_acl(path, version, acl, void_cb)
• a_get_acl(path, acl_cb)
• add_auth(scheme, auth)

The watcher methods are forward-looking subscriptions that can recieve multiple callbacks whenever a matching event occurs.

• aw_exists(path, watch_cb, stat_cb)
• aw_get(path, watch_cb, data_cb)
• aw_get_children(path, watch_cb, child_cb)
• aw_get_children2(path, watch_cb, child2_cb)

Callback Signatures

• path_cb : function(rc, error, path)
• stat_cb : function(rc, error, stat)
• data_cb : function(rc, error, stat, data)
• child_cb : function(rc, error, children)
• child2_cb : function(rc, error, children, stat)
• value_cb : function(rc, error, value)
• void_cb : function(rc, error)
• watch_cb : function(type, state, path)
• acl_cb : function(rc, error, acl, stat)
• connect_cb: function(err, zookeeper)

Input Parameters

• options : object. valid keys: { connect, timeout, debug_level, host_order_deterministic, data_as_buffer}
• path : string
• data : string or Buffer
• flags : int32
• version : int32
• watch : boolean
• scheme : authorisation scheme (digest, auth)
• auth : authorisation credentials (username:password)
• acl : acls list (same as output parameter, look below) - read only

Output Parameters

• path is a string
• data is either a Buffer (default), or a string (this is controlled by data_as_buffer = true/false)
• children is an array of strings
• rc is an int (error codes from zk api)
• error is a string (error string from zk api)
• type is an int event type (from zk api)
• state is an int (state when the watcher fired from zk api)
• stat is an object with the following attributes:
  • long czxid // created zxid
  • long mzxid // last modified zxid
  • long ctime // created
  • long mtime // last modified
  • int version // version
  • int cversion // child version
  • int aversion // acl version
  • string ephemeralOwner // owner session id if ephemeral, 0 otw
  • int dataLength // length of the data in the node
  • int numChildren // number of children of this node
  • long pzxid // last modified children
• acl is an array of acls objects, single acl object has following key
  • int perms // permisions
  • string scheme // authorisation scheme (digest, auth)
  • string auth // authorisation credentials (username:hashed_password)
• zookeeper is the ZooKeeper instance on which connect was called

Session state machine is well described in the Zookeeper docs

ACL and authorisation

The library comes with 3 default ACL levels defined (comes from ZK):

• ZooKeeper.ZOO_OPEN_ACL_UNSAFE - anyone can do anything
• ZooKeeper.ZOO_READ_ACL_UNSAFE - anyone can read
• ZooKeeper.ZOO_CREATOR_ALL_ACL - gives full rights to authorised user (you have to be authorised first, otherwise it will result with "invalid acl")

If you don't want to use predefined ACLs you can define your own (the ACL object is described above), for limiting permisions you can use:

• ZooKeeper.ZOO_PERM_READ - read permission
• ZooKeeper.ZOO_PERM_WRITE - write permission
• ZooKeeper.ZOO_PERM_CREATE - create permission
• ZooKeeper.ZOO_PERM_DELETE - delete permission
• ZooKeeper.ZOO_PERM_ADMIN - admin permission
• ZooKeeper.ZOO_PERM_ALL - all of the above

For more details please refer to ZooKeeper docs.

Windows support

Install CMake to build a ZooKeeper client on Windows. Python 2.7.x is currently required by the tool node-gyp to build the ZooKeeper client as a native Node.js Addon.

Also, run npm install in a Powershell window. For further instructions visit node-gyp documentation.

Windows support has been enabled mainly for supporting development, not for production.

Development

To run full output during the module build one has to use ZK_INSTALL_VERBOSE flag.

ZK_INSTALL_VERBOSE=1 npm install

For Windows (PowerShell): verbose build

$env:ZK_INSTALL_VERBOSE=1 
npm install

This PowerShell command will remove the environment variable:

Remove-Item Env:\ZK_INSTALL_VERBOSE

Implementation Notes

• Zookeeper C API library comes in 2 flavours: single-threaded and multi-threaded. For node.js, single-threaded library provides the most sense since all events coming from ZK responses have to be dispatched to the main JS thread.
• The C++ code uses the same logging facility that ZK C API uses internally. Hence zk_log.h file checked into this project. The file is considered ZK internal and is not installed into /usr/local/include
• Multiple simultaneous ZK connections are supported and tested
• All ZK constants are exposed as read-only properties of the ZooKeeper function, like ZK.ZOO_EPHEMERAL
• All ZK API methods including watchers are supported.

Known Bugs & Issues

• The lib will segfault if you try to use a ZooKeeper intance after the on_closed event is delivered (possibly as a result of session timeout etc.) YOU MAY NOT re-use the closed ZooKeeper instance. You should allocate a new one and initialize it as a completely new client. Any and all watchers from your first instance are lost, though they may fire (before the on_close) see below.
• Any established watches may/will be fired once each when/if your client is expired by the ZK server, the input arguments are observed to be: type=-1, state=1, path="". Care should be taken to handle this differently than a "real" watch event if that matters to your application.

Contribute to the project

Check out the issues tab and grab one! Read the contributing document.

See Also

• http://zookeeper.apache.org/releases.html
• http://zookeeper.apache.org/doc/current/zookeeperProgrammers.html#ZooKeeper+C+client+API

Acknowledgments

• node-webworker by pgriess is used to spawn multiple ZK workers in one of the tests.

LICENSE

See LICENSE-MIT.txt file in the top level folder.

ORIGINAL AUTHOR

Yuri Finkelstein (yurif2003 at yahoo dot com)

with awesome contributions from:

• Woody Anderson (Woodya)
• Dave Dopson (ddopson)
• Ryan Phillips (rphillips)
• David Trejo (DTrejo)
• Mark Cavage (mcavage)
• Jakub Lekstan (kuebk)
• Matt Lavin (mdlavin)
• David Vujic (davidvujic)

Changelog

v 4.4.0 (2019-08-11)

• fix: typos in the code documentation for async get_children.
• fix: retry download the ZooKeeper C Client if failed during npm install.
• feature: use v3.5.5 of the ZooKeeper C Client.