kazoo 2.3.0

Kazoo
=====




`kazoo` implements a higher level API to [Apache
Zookeeper](http://zookeeper.apache.org/) for Python clients.

See [the full docs](http://kazoo.rtfd.org/) for more information.

License
-------

`kazoo` is offered under the Apache License 2.0.

Authors
-------

`kazoo` started under the [Nimbus
Project](http://www.nimbusproject.org/) and through collaboration with
the open-source community has been merged with code from
[Mozilla](http://www.mozilla.org/) and the [Zope
Corporation](http://zope.com/). It has since gathered an active
community of over fifty contributors.


Changelog
=========

2.3.0 (2017-05-31)
------------------

Please note, there have been a few dozen merges that failed to update the
changelog here. As such, the log here should not be considered conclusive as
to the changes that are arriving in 2.3.0.

Changes being made now to ensure more accuracy in the changelog will appear
in all future versions going forward. Read the commit history for a better
understanding of changes merged between 2.2.1 and 2.3.0.

All future commits must abide by the new CONTRIBUTING.md document describing
how to label commits so they can be automatically used to automatically
generate an accurate changelog.

*WARNING:* THIS IS THE LAST KAZOO RELEASE THAT SUPPORTS PYTHON 2.6. ALL FUTURE
VERSIONS WILL REQUIRE PYTHON 2.7 AND ABOVE.

### Features

- allow having observers and different sized clusters

### Bug Handling

- \#372: fully resolve multiple records for hosts in the zookeeper
connection string

### Documentation

- Fix the recipe examples, so they actually work by connecting to
ZooKeeper. Without start() they just hang and can't be killed.

2.2.1 (2015-06-17)
------------------

### Bug Handling

- handle NameError with basestring on py3k.

### Documentation

2.2 (2015-06-15)
----------------

### Documentation

### Features

- Issue \#234: Add support for reconfig cluster membership operation

### Bug Handling

- \#315: multiple acquires of a kazoo lock using the lock recipe would
block when using acquire even when non-blocking is specified (only
when the lock was/has been already acquired).
- \#318: At exit register takes `*args` and `**kwargs` not args and
kargs

### Documentation

2.1 (2015-05-11)
----------------

### Features

- Start running tests against Zookeeper 3.5.0 alpha and explicitly
configure the admin.serverPort in tests to avoid port conflicts. The
Zookeeper alpha version is not yet officially supported.
- Integrate eventlet *handler* support into kazoo so that along with
[gevent, threading] handlers there can now be a dedicated eventlet
handler for projects that need to (or want to) use eventlet (such as
those working in the openstack community). The
`requirements_eventlet.txt` file lists the optional eventlet
requirement(s) that needs to be satisfied when this new handler is
used.
- Use `six` to nicely handle the cross compatibility of kazoo with
python 2.x and 3.x (reducing/removing the need to have custom
compatibility code that replicates what six already provides).
- Add `state_change_event` to
`kazoo.recipe.partitioner.SetPartitioner` which is set on every
state change.
- Add a NonBlockingLease recipe. The recipe allows e.g. cron jobs
scheduled on multiple machines to ensure that at most N instances
will run a particular job, with lease timeout for graceful handover
in case of node failures.

### Bug Handling

- \#291: Kazoo lock recipe was only partially re-entrant in that
multiple calls to acquire would obtain the the lock but the first
call to release would remove the underlying lock. This would leave
the X - 1 other acquire statements unprotected (and no longer
holding there expected lock). To fix this the comment about that
lock recipe being re-entrant has been removed and multiple acquires
will now block when attempted.
- \#78: Kazoo now uses socketpairs instead of pipes making it
compatible with Windows.
- \#144, \#221: Let client.command work with IPv6 addresses.
- \#216: Fixed timeout for ConnectionHandler.\_invoke.
- \#261: Creating a sequential znode under / doesn't work.
- \#274: Add server\_version() retries (by default 4 attempts will be
made) to better handle flakey responses.
- \#271: Fixed handling of KazooState.SUSPENDED in SetPartitioner.
- \#283: Fixed a race condition in SetPartitioner when party changes
during handling of lock acquisition.
- \#303: don't crash on random input as the hosts string.

### Documentation

- \#222: Document that committed on the transaction is used to ensure
only one commit and is not an indicator of whether operations in the
transaction returned desired results.

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.