ndServiceRegistry 0.1.0

Nextdoor ServiceRegistry module for interacting with Apache Zookeeper.

`ndServiceRegistry` is a Python module that provides a simple way to leverage `Apache Zookeeper` as a dynamic configuration and service registry.

The goal of the package is to provide a single foundational class that can be leveraged by any Python program for registering and monitoring services through Zookeeper.

The current use cases are: - Register a server providing a service - Retrieve a list of servers providing a particular service - Execute callback methods whenever a service list changes

The main benefit of using this module is if you have several different tools in your network that all need to interact with Zookeeper in a common way. The most common functions are handled in this singular module allowing you to focus on your own app development more.

Installation

To install, run

python setup.py install

or

pip install ndServiceRegistry

Instantiating a KazooServiceRegistry module

Create a logger object:

>>> import logging
>>> logger = logging.getLogger()
>>> logger.setLevel(logging.DEBUG)
>>> handler = logging.StreamHandler()
>>> logger.addHandler(handler)

To create your initial connection object:

>>> from ndServiceRegistry import KazooServiceRegistry
>>> nd = KazooServiceRegistry()

The KazooServiceRegistry object is a child of ndServiceRegistry that conforms to our ServiceRegistry specs, whlie leveraging Kazoo as the backend. The object handles all of your connection states - there is no need to start/stop or monitor the connection state at all.

Basic use

To register the host as providing a particular service:

>>> nd.set_node('/services/ssh/server1:22', data={ 'foo': 'bar'})

Getting a list of servers at a path:

>>> nd.get('/services/ssh')
{'children': {u'server1:22': {u'foo': u'bar',
                              u'created': u'2012-12-15 00:45:03',
                              u'pid': 10733}},
 'data': None,
 'path': '/services/ssh',
 'stat': ZnodeStat(czxid=6, mzxid=6, ctime=1355532303688,
                   mtime=1355532303688, version=0, cversion=1,
                   aversion=0, ephemeralOwner=0, dataLength=0,
                   numChildren=1, pzxid=7)}

Failure Handling

The goal of this module is to be as self-contained as possible and require as little code in your app as possible. To that end, we almost never raise an Exception once the module is loaded up and connected.

We do raise a few exceptions, and each one is documented here. Whenever we can though, we instead just return False as a way of indicating that we were unable to perform your command now … but that we will take care of it later. Whenever we do this, we throw a WARNING log message as well.

ndServiceRegistry.exceptions.NoConnection

Thrown if you attempt any operation that requires immediate access to the backend Zookeeper service. Either a set() operation, or a get() operation on a path for the first time.

Also thrown during initial connection to Zookeeper, if lazy=False.

(It should be noted, a get() will actually return the cached results even if Zookeeper is down. This allows the service to fail temporarily in the background but your app is still able to get the ‘last known’ results.)

ndServiceRegistry.exceptions.ReadOnly

If readonly=True, any operation that would result in a ‘write’ will throw this exception. Most notably, a set() operation will fail with this exception if readonly=True.

API Documentation

Detailed implementation details and instructions are in the individual library files.