hash-ring-ctypes

Fast ctypes-based wrapper around libhashring.

What is a hash ring? Check this out.

Installation

For now, clone from this repo:

$ pip install -e git+https://github.com/mattdennewitz/hash-ring-ctypes#egg=hash_ring

Usage

Documentation online at Read the Docs.

But here's a quick example! Let's say that you want to increase parallel downloads of your site's assets by the browser via domain sharding. You've created four CNAME records pointing to your CDN, cdn.example.com, cdn2.example.com, cdn3.example.com, and cdn4.example.com, and you want to use a hash ring to select which address will serve a specific asset.

import hash_ring

# create a ring with nodes with 10 replicas
# and a handful of nodes
nodes = ['cdn1.example.com', 'cdn2.example.com',
         'cdn3.example.com', 'cdn4.example.com']
ring = hash_ring.HashRing(replicas=10, nodes=nodes)

# or create an empty ring with the default number of replicas (5)
# and add nodes manually
ring = hash_ring.HashRing()
map(ring.add_node, nodes)

Now that you have a ring, you can find which domain you should use to serve a specific asset. In this case, we'll look up which domain matches artwork/1/header.jpg.

# look up a node for a certain value, like a filename
cdn_endpoint = ring.lookup('artwork/1/header.jpg')

Tests

To run tests, run tests.py.

$ python tests.py

Further Reading

• Consistent hashing
• libhashring