Swimpy is a Python library which implements a gossip membership and failure detection protocol based on the SWIM whitepaper. Swimpy will, given a list of seed nodes, attempt to join and maintain a list of all non-failing members of the cluster. Lots of inspiration taken from Hashicorp's Memberlist.

Swimpy talks to other nodes using msgpack RPC over TCP sockets, via nonblocking io (Tornado). While there hasn't yet been any benchmarking, it seems very snappy.

The swimpy.runtime.Runtime.start() method forks a child process that handles the SWIM backend asynchronously. Consumers of this libary don't need to worry about the Tornado ioloop, and can be written with basically any framework.

from swimpy import Runtime


# Create three swimpy Runtime objects
n1 = Node(node_id='node-1', addr='127.0.0.1', port=9000)
r1 = Runtime(routes=ROUTES, node=n1)

# Configure a list of seed nodes to join on startup
n2 = Node(node_id='node-2', addr='127.0.0.1', port=9001)
r2 = Runtime(routes=ROUTES, node=n2, seed_nodes=[('127.0.0.1', 9000)])

n3 = Node(node_id='node-3', addr='127.0.0.1', port=9002)
r3 = Runtime(routes=ROUTES, node=n3, seed_nodes=[('127.0.0.1', 9001)])

try:
    r1.start()
    r2.start()
    r3.start()

    # Verify that the cluster has converged
    for runtime in [r1, r2, r3]:
        nodes_dict = runtime.nodes
        assert sorted(nodes_dict) == ['node-1', 'node-2', 'node-3']

finally:
    r1.stop()
    r2.stop()
    r3.stop()

• Pings are sent at fuzzy intervals (ie. jitter)
• Add support for UDP handlers
• Migrate gossip dissemination to UDP

• Nodes ping each other regularly
• Nodes check that PINGs and ACKs have matching sequence numbers
• Nodes attach gossip messages to ACK replies
• Nodes add new ALIVE nodes from their node list
• Nodes mark nodes failing pings as SUSPECT
• Nodes ask peers to doublecheck SUSPECT nodes
• Nodes mark SUSPECT nodes failing pings as DEAD
• Nodes remove DEAD nodes from their node list

• Nodes can advertise themselves to other nodes
• Nodes receive and disseminate membership data via gossip
• Nodes learn about other nodes indirectly via dissemination

• Unit test coverage > 50%
• Unit test coverage > 80%
• Unit test coverage, 100%
• Integration tests > 50%
• Integration tests > 80%
• Integration tests, 100%

1. Please update the CHANGELOG
2. Create a virtualenv and run python setup.py develop
3. Run unit tests via py.test or python setup.py test
4. Run integration tests via py.test -m 'integration'

MIT