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clandestined

rendezvous hashing implementation based on murmur3 hash

motivation

in distributed systems, the need often arises to locate objects amongst a cluster of machines. consistent hashing and rendezvous hashing are methods of performing this task, while minimizing data movement on cluster topology changes.

clandestined is a library for rendezvous hashing which has the goal of simple clients and ease of use.

Currently Supported Interpreters:

  • Python 2.5 through Python 3.8
  • PyPy and PyPy3

Build Status

example usage

>>> from clandestined import Cluster
>>>
>>> nodes = {
...     '1': {'name': 'node1.example.com', 'zone': 'us-east-1a'},
...     '2': {'name': 'node2.example.com', 'zone': 'us-east-1a'},
...     '3': {'name': 'node3.example.com', 'zone': 'us-east-1a'},
...     '4': {'name': 'node4.example.com', 'zone': 'us-east-1b'},
...     '5': {'name': 'node5.example.com', 'zone': 'us-east-1b'},
...     '6': {'name': 'node6.example.com', 'zone': 'us-east-1b'},
...     '7': {'name': 'node7.example.com', 'zone': 'us-east-1c'},
...     '8': {'name': 'node8.example.com', 'zone': 'us-east-1c'},
...     '9': {'name': 'node9.example.com', 'zone': 'us-east-1c'},
... }
>>>
>>> cluster = Cluster(nodes)
>>> cluster.find_nodes('mykey')
['4', '8']
>>>

by default, Cluster will place 2 replicas around the cluster taking care to place the second replica in a separate zone from the first.

in the event that your cluster doesn't need zone awareness, you can either invoke the RendezvousHash class directly, or use a Cluster with replicas set to 1

>>> from clandestined import Cluster
>>> from clandestined import RendezvousHash
>>>
>>> nodes = {
...     '1': {'name': 'node1.example.com'},
...     '2': {'name': 'node2.example.com'},
...     '3': {'name': 'node3.example.com'},
...     '4': {'name': 'node4.example.com'},
...     '5': {'name': 'node5.example.com'},
...     '6': {'name': 'node6.example.com'},
...     '7': {'name': 'node7.example.com'},
...     '8': {'name': 'node8.example.com'},
...     '9': {'name': 'node9.example.com'},
... }
>>>
>>> cluster = Cluster(nodes, replicas=1)
>>> rendezvous = RendezvousHash(nodes.keys())
>>>
>>> cluster.find_nodes('mykey')
['4']
>>> rendezvous.find_node('mykey')
'4'
>>>

advanced usage

murmur3 seeding

DISCLAIMER

clandestined was not designed with consideration for untrusted input, please see LICENSE.

END DISCLAIMER

if you plan to use keys based on untrusted input (not supported, but go ahead), it would be best to use a custom seed for hashing. although this technique is by no means a way to fully mitigate a DoS attack using crafted keys, it may make you sleep better at night.

>>> from clandestined import Cluster
>>> from clandestined import RendezvousHash
>>>
>>> nodes = {
...     '1': {'name': 'node1.example.com'},
...     '2': {'name': 'node2.example.com'},
...     '3': {'name': 'node3.example.com'},
...     '4': {'name': 'node4.example.com'},
...     '5': {'name': 'node5.example.com'},
...     '6': {'name': 'node6.example.com'},
...     '7': {'name': 'node7.example.com'},
...     '8': {'name': 'node8.example.com'},
...     '9': {'name': 'node9.example.com'},
... }
>>>
>>> cluster = Cluster(nodes, replicas=1, seed=1337)
>>> rendezvous = RendezvousHash(nodes.keys(), seed=1337)
>>>
>>> cluster.find_nodes('mykey')
['7']
>>> rendezvous.find_node('mykey')
'7'
>>>

contributors

Thanks to the following contributors for their aid in making this project great: