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From Jordan Zimmerman <>
Subject [PROPOSAL] Curator for the Apache Incubator
Date Tue, 26 Feb 2013 01:14:36 GMT

I would like to propose that Curator to be an Apache Incubator project.

The proposal can be found here:

I have included the contents of the proposal below.


Jordan Zimmerman


= Curator - ZooKeeper client wrapper and rich ZooKeeper framework =

== Abstract ==

Curator is a set of Java libraries that make using Apache ZooKeeper much easier. While ZooKeeper
comes bundled with a Java client, using the client is non-trivial and error prone.

== Proposal ==

Curator is a set of Java libraries that make using Apache ZooKeeper much easier. While ZooKeeper
comes bundled with a Java client, using the client is non-trivial and error prone. It consists
of three components that build on each other. Curator Client is a replacement for the bundled
ZooKeeper class that takes care of some low-level housekeeping and provides some useful utilities.
Curator Framework is a high-level API that greatly simplifies using ZooKeeper. It adds many
features that build on ZooKeeper and handles the complexity of managing connections to the
ZooKeeper cluster and retrying operations. Curator Recipes consists of implementations of
some of the common ZooKeeper “recipes”. Additionally, Curator Test is included which includes
utilities to help with unit testing ZooKeeper-based applications.

== Background ==

Curator was initially developed by Netflix to make writing ZooKeeper-based applications easier
and more reliable. Curator was open-sourced by Netflix on !GitHub as an Apache 2.0 licensed
project in July 2011. During this time Curator has been formally released many times and has
gained widespread adoption.

== Rationale ==

New users of ZooKeeper are surprised to learn that a significant amount of connection management
must be done manually. For example, when the ZooKeeper client connects to the ensemble it
must negotiate a new session, etc. This takes some time. If you use a ZooKeeper client API
before the connection process has completed, ZooKeeper will throw an exception. These types
of exceptions are referred to as “recoverable” errors. 
Curator automatically handles connection management, greatly simplifying client code. Instead
of directly using the ZooKeeper APIs you use Curator APIs that internally check for connection
completion and wrap each ZooKeeper API in a retry loop. Curator uses a retry mechanism to
handle recoverable errors and automatically retry operations. The method of retry is customizable.
Curator comes bundled with several implementations (ExponentialBackoffRetry, etc.) or custom
implementations can be written.

The ZooKeeper documentation describes many possible uses for ZooKeeper calling each a “recipe”.
While the distribution comes bundled with a few implementations of these recipes, most ZooKeeper
users will need to manually implement one or more of the recipes. Implementing a ZooKeeper
recipe is not trivial. Besides the connection handling issues, there are numerous edge cases
that are not well documented that must be considered. For example, many recipes require that
an ephemeral-sequential node be created. New users of ZooKeeper will not know that there is
an edge case in ephemeral-sequential node creation that requires you to put a special “marker”
in the node’s name so that you can search for the created node if an I/O failure occurs.
This is but one of many edge cases that are not well documented but are handled by Curator.

= Current Status =

== Meritocracy ==

Curator was initially developed by Jordan Zimmerman in 2011 at Netflix. Developers external
to Netflix provided feedback, suggested features and fixes and implemented extensions of Curator.
Netflix's engineering team has since maintained the project and has been dedicated towards
its improvement. Contributors to Curator include developers from multiple organizations around
the world. Curator will be a meritocracy as it enters the Incubator and beyond.

== Community ==

Curator is currently used by a number of organizations all over the world. Curator has an
active and growing user and developer community with active participation in the [[]]
mailing list and at its !Github home: [[]].

Since open sourcing the project, there have been fifteen individuals from various organizations
who have contributed code.

== Core Developers ==

The core developers for Curator are:
 * Jordan Zimmerman
 * Jay Zarfoss

Jordan has contributed towards Apache ZooKeeper and both Jordan and Jay are familiar with
Apache principles and philosophy for community driven software development.

== Alignment ==

Curator is a natural complement for Apache ZooKeeper. Java users of ZooKeeper will naturally
want to use Curator. When Curator graduates from Incubator it may be useful to distribute
Curator artifacts as part of ZooKeeper releases as the preferred/recommended client side library.
Further, at graduation a determination can be made as to whether Curator should become a Top
Level Project or be merged into ZooKeeper itself.

= Known Risks =

== Orphaned Products ==

Curator is already deployed in production at multiple companies and they are actively participating
in creating new features. Curator is getting traction with developers and thus the risks of
it being orphaned are minimal.

== Inexperience with Open Source ==

All code developed for Curator has been open sourced by Netflix under Apache 2.0 license.
 All committers to Curator are intimately familiar with the Apache model for open-source development
and are experienced with working with new contributors.

== Homogeneous Developers ==

The initial committers are from a single organization. However, we expect that once approved
for incubation, the project will attract new contributors from diverse organizations and will
thus grow organically. The submission of patches from developers from several different organizations
is a strong indication that Curator will be widely adopted.

== Reliance on Salaried Developers ==

It is expected that Curator will be developed on salaried and volunteer time, although all
of the initial developers will work on it mainly on salaried time.

== Relationships with Other Apache Products ==

Curator depends upon other Apache Projects: Apache ZooKeeper, Apache Log4J, and multiple Apache
Commons components. Its build depends upon Apache Maven. Notably, there is interest from other
Apache Projects such as HBase in adopting Curator as the client library for ZooKeeper. Apache
James Mailbox has already incorporated Curator.

== An Excessive Fascination with the Apache Brand ==

We would like Curator to become an Apache project to further foster a healthy community of
contributors and consumers around the project.  Since Curator directly interacts with Apache
ZooKeeper and solves an important problem of many ZooKeeper users, residing in the Apache
Software Foundation will increase interaction with the larger community.

= Documentation =

 * Curator wiki at GitHub:
 * Curator issues at GitHub:
 * Curator javadoc at GitHub:

= Initial Source =

 * git://

== Source and Intellectual Property Submission Plan ==

 * The initial source is already licensed under the Apache License, Version 2.0.

== External Dependencies ==

The required external dependencies are all Apache License or compatible licenses. Following
components with non-Apache licenses are enumerated:

 * org.slf4j: MIT-like License
 * org.mockito: MIT-like License

== Cryptography ==

Curator contains no known cryptography.

= Required Resources =

== Mailing lists ==

 * curator-private (with moderated subscriptions)
 * curator-dev
 * curator-commits
 * curator-user

== Github Repositories == git://

== Issue Tracking ==


== Other Resources ==

The existing code already has unit and integration tests so we would like a Jenkins instance
to run them whenever a new patch is submitted. This can be added after project creation.

= Initial Committers =

 * Jordan Zimmerman (jzimmerman at netflix dot com)
 * Jay Zarfoss (jzarfoss at netflix dot com)

= Affiliations =

 * Jordan Zimmerman, Netflix
 * Jay Zarfoss, Netflix

= Sponsors =

== Champion ==

 * Patrick Hunt

== Nominated Mentors ==

 * Patrick Hunt
 * Enis Söztutar
 * Mahadev Konar

== Sponsoring Entity ==

 * Apache Incubator PMC
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