kazoo.yandex 2.0dev
Higher Level Zookeeper Client
License: Apache 2.0
Keywords: zookeeper lock leader configuration

=====
Kazoo
=====

``kazoo`` implements a higher level API to `Apache Zookeeper`_ for Python
clients.

See `the full docs`_ for more information.

License
=======

``kazoo`` is offered under the Apache License 2.0.

Authors
=======

``kazoo`` started under the `Nimbus Project`_ and through collaboration with
the open-source community has been merged with code from `Mozilla`_ and the
`Zope Corporation`_. It has since gathered an active community of over two
dozen contributors.

.. _Apache Zookeeper: http://zookeeper.apache.org/
.. _the full docs: http://kazoo.rtfd.org/
.. _Nimbus Project: http://www.nimbusproject.org/
.. _Zope Corporation: http://zope.com/
.. _Mozilla: http://www.mozilla.org/


Changelog
=========

2.0 (2014-06-19)
----------------

Documentation
*************

- Extend support to Python 3.4, deprecating Python 3.2.
- Issue #198: Mention Zake as a sophisticated kazoo mock testing library.
- Issue #181: Add documentation on basic logging setup.

2.0b1 (2014-04-24)
------------------

API Changes
***********

- Null or None data is no longer treated as "". Pull req #165, patch by
  Raul Gutierrez S. This will affect how you should treat null data in a
  znode vs. an empty string.
- Passing acl=[] to create() now works properly instead of an InvalidACLError
  as it returned before. Patch by Raul Gutierrez S in PR #164.
- Removed the dependency on zope.interface. The classes in the interfaces
  module are left for documentation purposes only (issue #131).

Features
********

- Logging levels have been reduced.

  - Logging previously at the ``logging.DEBUG`` level is now logged at
    the ``kazoo.loggingsupport.BLATHER`` level (5).

  - Some low-level logging previously at the ``logging.INFO`` level is
    now logged at the ``logging.DEBUG`` level.

- Issue #133: Introduce a new environment variable `ZOOKEEPER_PORT_OFFSET`
  for the testing support, to run the testing cluster on a different range.

Bug Handling
************

- When authenticating via add_auth() the auth data will be saved to ensure that
  the authentication happens on reconnect (as is the case when feeding auth
  data via KazooClient's constructor). PR #172, patch by Raul Gutierrez S.
- Change gevent import to remove deprecation warning when newer gevent is
  used. PR #191, patch by Hiroaki Kawai.
- Lock recipe was failing to use the client's sleep_func causing issues with
  gevent. Issue #150.
- Calling a DataWatch or ChildrenWatch instance twice (decorator) now throws
  an exception as only a single function can be associated with a single
  watcher. Issue #154.
- Another fix for atexit handling so that when disposing of connections the
  atexit handler is removed. PR #190, patch by Devaev Maxim.
- Fix atexit handling for kazoo threading handler, PR #183. Patch by
  Brian Wickman.
- Partitioner should handle a suspended connection properly and restore
  an allocated state if it was allocated previously. Patch by Manish Tomar.
- Issue #167: Closing a client that was never started throws a type error.
  Patch by Joshua Harlow.
- Passing dictionaries to KazooClient.__init__() wasn't actually working
  properly. Patch by Ryan Uber.
- Issue #119: Handler timeout takes the max of the random interval or
  the read timeout to ensure a negative number isn't used for the read
  timeout.
- Fix ordering of exception catches in lock.acquire as it was capturing a
  parent exception before the child. Patch by ReneSac.
- Fix issue with client.stop() not always setting the client state to
  KeeperState.CLOSED. Patch by Jyrki Pulliainen in PR #174.
- Issue #169: Fixed pipes leaking into child processes.

Documentation
*************

- Add section on contributing recipes, add maintainer/status information for
  existing recipes.
- Add note about alternate use of DataWatch.

1.3.1 (2013-09-25)
------------------

Bug Handling
************

- #118, #125, #128: Fix unknown variable in KazooClient `command_retry`
  argument handling.

- #126: Fix `KazooRetry.copy` to correctly copy sleep function.

- #118: Correct session/socket timeout conversion (int vs. float).

Documentation
*************

- #121: Add a note about `kazoo.recipe.queue.LockingQueue` requiring a
  Zookeeper 3.4+ server.


1.3 (2013-09-05)
----------------

Features
********

- #115: Limit the backends we use for SLF4J during tests.

- #112: Add IPv6 support. Patch by Dan Kruchinin.

1.2.1 (2013-08-01)
------------------

Bug Handling
************

- Issue #108: Circular import fail when importing kazoo.recipe.watchers
  directly has now been resolved. Watchers and partitioner properly import
  the KazooState from kazoo.protocol.states rather than kazoo.client.
- Issue #109: Partials not usable properly as a datawatch call can now be
  used. All funcs will be called with 3 args and fall back to 2 args if
  there's an argument error.
- Issue #106, #107: `client.create_async` didn't strip change root from the
  returned path.

1.2 (2013-07-24)
----------------

Features
********

- KazooClient can now be stopped more reliably even if its in the middle
  of a long retry sleep. This utilizes the new interrupt feature of
  KazooRetry which lets the sleep be broken down into chunks and an
  interrupt function called to determine if the retry should fail early.

- Issue #62, #92, #89, #101, #102: Allow KazooRetry to have a
  max deadline, transition properly when connection fails to LOST, and
  setup separate connection retry behavior from client command retry
  behavior. Patches by Mike Lundy.

- Issue #100: Make it easier to see exception context in threading and
  connection modules.

- Issue #85: Increase information density of logs and don't prevent
  dynamic reconfiguration of log levels at runtime.

- Data-watchers for the same node are no longer 'stacked'. That is, if
  a get and an exists call occur for the same node with the same watch
  function, then it will be registered only once. This change results in
  Kazoo behaving per Zookeeper client spec regarding repeat watch use.

Bug Handling
************

- Issue #53: Throw a warning upon starting if the chroot path doesn't exist
  so that it's more obvious when the chroot should be created before
  performing more operations.

- Kazoo previously would let the same function be registered as a data-watch
  or child-watch multiple times, and then call it multiple times upon being
  triggered. This was non-compliant Zookeeper client behavior, the same
  watch can now only be registered once for the same znode path per Zookeeper
  client documentation.

- Issue #105: Avoid rare import lock problems by moving module imports in
  client.py to the module scope.

- Issue #103: Allow prefix-less sequential znodes.

- Issue #98: Extend testing ZK harness to work with different file locations
  on some versions of Debian/Ubuntu.

- Issue #97: Update some docstrings to reflect current state of handlers.

- Issue #62, #92, #89, #101, #102: Allow KazooRetry to have a
  max deadline, transition properly when connection fails to LOST, and
  setup separate connection retry behavior from client command retry
  behavior. Patches by Mike Lundy.

API Changes
***********

- The `kazoo.testing.harness.KazooTestHarness` class directly inherits from
  `unittest.TestCase` and you need to ensure to call its `__init__` method.

- DataWatch no longer takes any parameters besides for the optional function
  during instantiation. The additional options are now implicitly True, with
  the user being left to ignore events as they choose. See the DataWatch
  API docs for more information.

- Issue #99: Better exception raised when the writer fails to close. A
  WriterNotClosedException that inherits from KazooException is now raised
  when the writer fails to close in time.

1.1 (2013-06-08)
----------------

Features
********

- Issue #93: Add timeout option to lock/semaphore acquire methods.

- Issue #79 / #90: Add ability to pass the WatchedEvent to DataWatch and
  ChildWatch functions.

- Respect large client timeout values when closing the connection.

- Add a `max_leases` consistency check to the semaphore recipe.

- Issue #76: Extend testing helpers to allow customization of the Java
  classpath by specifying the new `ZOOKEEPER_CLASSPATH` environment variable.

- Issue #65: Allow non-blocking semaphore acquisition.

Bug Handling
************

- Issue #96: Provide Windows compatibility in testing harness.

- Issue #95: Handle errors deserializing connection response.

- Issue #94: Clean up stray bytes in connection pipe.

- Issue #87 / #88: Allow re-acquiring lock after cancel.

- Issue #77: Use timeout in initial socket connection.

- Issue #69: Only ensure path once in lock and semaphore recipes.

- Issue #68: Closing the connection causes exceptions to be raised by watchers
  which assume the connection won't be closed when running commands.

- Issue #66: Require ping reply before sending another ping, otherwise the
  connection will be considered dead and a ConnectionDropped will be raised
  to trigger a reconnect.

- Issue #63: Watchers weren't reset on lost connection.

- Issue #58: DataWatcher failed to re-register for changes after non-existent
  node was created then deleted.

API Changes
***********

- KazooClient.create_async now supports the makepath argument.

- KazooClient.ensure_path now has an async version, ensure_path_async.

1.0 (2013-03-26)
----------------

Features
********

- Added a LockingQueue recipe. The queue first locks an item and removes it
  from the queue only after the consume() method is called. This enables other
  nodes to retake the item if an error occurs on the first node.

Bug Handling
************

- Issue #50: Avoid problems with sleep function in mixed gevent/threading
  setup.

- Issue #56: Avoid issues with watch callbacks evaluating to false.

1.0b1 (2013-02-24)
------------------

Features
********

- Refactored the internal connection handler to use a single thread. It now
  uses a deque and pipe to signal the ZK thread that there's a new command to
  send, so that the ZK thread can send it, or retrieve a response.
  Processing ZK requests and responses serially in a single thread eliminates
  the need for a bunch of the locking, the peekable queue and two threads
  working on the same underlying socket.

- Issue #48: Added documentation for the `retry` helper module.

- Issue #55: Fix `os.pipe` file descriptor leak and introduce a
  `KazooClient.close` method. The method is particular useful in tests, where
  multiple KazooClients are created and closed in the same process.

Bug Handling
************

- Issue #46: Avoid TypeError in GeneratorContextManager on process shutdown.

- Issue #43: Let DataWatch return node data if allow_missing_node is used.

0.9 (2013-01-07)
----------------

API Changes
***********

- When a retry operation ultimately fails, it now raises a
  `kazoo.retry.RetryFailedError` exception, instead of a general `Exception`
  instance. `RetryFailedError` also inherits from the base `KazooException`.

Features
********

- Improvements to Debian packaging rules.

Bug Handling
************

- Issue #39 / #41: Handle connection dropped errors during session writes.
  Ensure client connection is re-established to a new ZK node if available.

- Issue #38: Set `CLOEXEC` flag on all sockets when available.

- Issue #37 / #40: Handle timeout errors during `select` calls on sockets.

- Issue #36: Correctly set `ConnectionHandler.writer_stopped` even if an
  exception is raised inside the writer, like a retry operation failing.

0.8 (2012-10-26)
----------------

API Changes
***********

- The `KazooClient.__init__` took as `watcher` argument as its second keyword
  argument. The argument had no effect anymore since version 0.5 and was
  removed.

Bug Handling
************

- Issue #35: `KazooClient.__init__` didn't pass on `retry_max_delay` to the
  retry helper.

- Issue #34: Be more careful while handling socket connection errors.

0.7 (2012-10-15)
----------------

Features
********

- DataWatch now has a `allow_missing_node` setting that allows a watch to be
  set on a node that doesn't exist when the DataWatch is created.
- Add new Queue recipe, with optional priority support.
- Add new Counter recipe.
- Added debian packaging rules.

Bug Handling
************

- Issue #31 fixed: Only catch KazooExceptions in catch-all calls.
- Issue #15 fixed again: Force sleep delay to be a float to appease gevent.
- Issue #29 fixed: DataWatch and ChildrenWatch properly re-register their
  watches on server disconnect.

0.6 (2012-09-27)
----------------

API Changes
***********

- Node paths are assumed to be Unicode objects. Under Python 2 pure-ascii
  strings will also be accepted. Node values are considered bytes. The byte
  type is an alias for `str` under Python 2.
- New KeeperState.CONNECTED_RO state for Zookeeper servers connected in
  read-only mode.
- New NotReadOnlyCallError exception when issuing a write change against a
  server thats currently read-only.

Features
********

- Add support for Python 3.2, 3.3 and PyPy (only for the threading handler).
- Handles connecting to Zookeeper 3.4+ read-only servers.
- Automatic background scanning for a Read/Write server when connected to a
  server in read-only mode.
- Add new Semaphore recipe.
- Add a new `retry_max_delay` argument to the client and by default limit the
  retry delay to at most an hour regardless of exponential backoff settings.
- Add new `randomize_hosts` argument to `KazooClient`, allowing one to disable
  host randomization.

Bug Handling
************

- Fix bug with locks not handling intermediary lock contenders disappearing.
- Fix bug with set_data type check failing to catch unicode values.
- Fix bug with gevent 0.13.x backport of peekable queue.
- Fix PatientChildrenWatch to use handler specific sleep function.

0.5 (2012-09-06)
----------------

Skipping a version to reflect the magnitude of the change. Kazoo is now a pure
Python client with no C bindings. This release should run without a problem
on alternate Python implementations such as PyPy and Jython. Porting to Python
3 in the future should also be much easier.

Documentation
*************

- Docs have been restructured to handle the new classes and locations of the
  methods from the pure Python refactor.

Bug Handling
************

This change may introduce new bugs, however there is no longer the possibility
of a complete Python segfault due to errors in the C library and/or the C
binding.

- Possible segfaults from the C lib are gone.
- Password mangling due to the C lib is gone.
- The party recipes didn't set their participating flag to False after
  leaving.

Features
********

- New `client.command` and `client.server_version` API, exposing Zookeeper's
  four letter commands and giving access to structured version information.
- Added 'include_data' option for get_children to include the node's Stat
  object.
- Substantial increase in logging data with debug mode. All correspondence with
  the Zookeeper server can now be seen to help in debugging.

API Changes
***********

- The testing helpers have been moved from `testing.__init__` into a
  `testing.harness` module. The official API's of `KazooTestCase` and
  `KazooTestHarness` can still be directly imported from `testing`.
- The kazoo.handlers.util module was removed.
- Backwards compatible exception class aliases are provided for now in kazoo
  exceptions for the prior C exception names.
- Unicode strings now work fine for node names and are properly converted to
  and from unicode objects.
- The data value argument for the create and create_async methods of the
  client was made optional and defaults to an empty byte string. The data
  value must be a byte string. Unicode values are no longer allowed and
  will raise a TypeError.


0.3 (2012-08-23)
----------------

API Changes
***********

- Handler interface now has an rlock_object for use by recipes.

Bug Handling
************

- Fixed password bug with updated zc-zookeeper-static release, which retains
  null bytes in the password properly.
- Fixed reconnect hammering, so that the reconnection follows retry jitter and
  retry backoff's.
- Fixed possible bug with using a threading.Condition in the set partitioner.
  Set partitioner uses new rlock_object handler API to get an appropriate RLock
  for gevent.
- Issue #17 fixed: Wrap timeout exceptions with staticmethod so they can be
  used directly as intended. Patch by Bob Van Zant.
- Fixed bug with client reconnection looping indefinitely using an expired
  session id.

0.2 (2012-08-12)
----------------

Documentation
*************

- Fixed doc references to start_async using an AsyncResult object, it uses
  an Event object.

Bug Handling
************

- Issue #16 fixed: gevent zookeeper logging failed to handle a monkey patched
  logging setup. Logging is now setup such that a greenlet is used for logging
  messages under gevent, and the thread one is used otherwise.
- Fixed bug similar to #14 for ChildrenWatch on the session listener.
- Issue #14 fixed: DataWatch had inconsistent handling of the node it was
  watching not existing. DataWatch also properly spawns its _get_data function
  to avoid blocking session events.
- Issue #15 fixed: sleep_func for SequentialGeventHandler was not set on the
  class appropriately leading to additional arguments being passed to
  gevent.sleep.
- Issue #9 fixed: Threads/greenlets didn't gracefully shut down. Handler now
  has a start/stop that is used by the client when calling start and stop that
  shuts down the handler workers. This addresses errors and warnings that could
  be emitted upon process shutdown regarding a clean exit of the workers.
- Issue #12 fixed: gevent 0.13 doesn't use the same start_new_thread as gevent
  1.0 which resulted in a fully monkey-patched environment halting due to the
  wrong thread. Updated to use the older kazoo method of getting the real thread
  module object.

API Changes
***********

- The KazooClient handler is now officially exposed as KazooClient.handler
  so that the appropriate sync objects can be used by end-users.
- Refactored ChildrenWatcher used by SetPartitioner into a publicly exposed
  PatientChildrenWatch under recipe.watchers.

Deprecations
************

- connect/connect_async has been renamed to start/start_async to better match
  the stop to indicate connection handling. The prior names are aliased for
  the time being.

Recipes
*******

- Added Barrier and DoubleBarrier implementation.

0.2b1 (2012-07-27)
------------------

Bug Handling
************

- ZOOKEEPER-1318: SystemError is caught and rethrown as the proper invalid
  state exception in older zookeeper python bindings where this issue is still
  valid.
- ZOOKEEPER-1431: Install the latest zc-zookeeper-static library or use the
  packaged ubuntu one for ubuntu 12.04 or later.
- ZOOKEEPER-553: State handling isn't checked via this method, we track it in
  a simpler manner with the watcher to ensure we know the right state.

Features
********

- Exponential backoff with jitter for retrying commands.
- Gevent 0.13 and 1.0b support.
- Lock, Party, SetPartitioner, and Election recipe implementations.
- Data and Children watching API's.
- State transition handling with listener registering to handle session state
  changes (choose to fatal the app on session expiration, etc.)
- Zookeeper logging stream redirected into Python logging channel under the
  name 'Zookeeper'.
- Base client library with handler support for threading and gevent async
  environments.