consensual 0.2.3

Implementation of raft consensus algorithm.

consensual

Summary

consensual is a pure-Python library for defining network of nodes running in a consistent fault-tolerant manner by implementing state-of-the-art Raft consensus algorithm.

Currently, next features are implemented & property-based tested

• leader election & log replication (described in section 5 of the article),
• cluster membership changes (described in section 6 of the article), namely consensual addition & removal of nodes,
• "solo mode": non-consensual separation of a node resulting in running as a cluster-by-itself,
• separate node state resetting with history deletion.

Next crucial features to implement will be

• persistence,
• log compaction (described in section 7 of the article).

---

In what follows python is an alias for python3.7 or any later version (python3.8 and so on).

Installation

Install the latest pip & setuptools packages versions

python -m pip install --upgrade pip setuptools

User

Download and install the latest stable version from PyPI repository

python -m pip install --upgrade consensual

Developer

Download the latest version from GitHub repository

git clone https://github.com/lycantropos/consensual.git
cd consensual

Install dependencies

python -m pip install -r requirements.txt

Install

python setup.py install

Usage

>>> from consensual.raft import Node, communication
>>> from yarl import URL
>>> node_url = URL.build(scheme='http',
...                      host='localhost',
...                      port=6000)
>>> other_node_url = URL.build(scheme='http',
...                            host='localhost',
...                            port=6001)
>>> heartbeat = 0.1
>>> from typing import Any, List, Optional
>>> processed_parameters = []
>>> def dummy_processor(parameters: Any) -> None:
...     processed_parameters.append(parameters)
>>> processors = {'dummy': dummy_processor}
>>> nodes = {}
>>> sender = communication.Sender([node_url], nodes)
>>> other_sender = communication.Sender([other_node_url], nodes)
>>> node = Node.from_url(node_url,
...                      heartbeat=heartbeat,
...                      processors=processors,
...                      sender=sender)
>>> other_node = Node.from_url(other_node_url,
...                            heartbeat=heartbeat,
...                            processors=processors,
...                            sender=other_sender)
>>> receiver = communication.Receiver(node, nodes)
>>> other_receiver = communication.Receiver(other_node, nodes)
>>> receiver.start()
>>> other_receiver.start()
>>> from asyncio import get_event_loop
>>> loop = get_event_loop()
>>> async def run() -> List[Optional[str]]:
...     return [await node.solo(),
...             await node.enqueue('dummy', 42),
...             await node.attach_nodes([other_node.url]),
...             await node.enqueue('dummy', 42),
...             await other_node.detach_nodes([node.url]),
...             await other_node.solo(),
...             await other_node.detach(),
...             await other_node.detach()]
>>> error_messages = loop.run_until_complete(run())
>>> receiver.stop()
>>> other_receiver.stop()
>>> all(error_message is None or isinstance(error_message, str)
...     for error_message in error_messages)
True
>>> all(parameters == 42 for parameters in processed_parameters)
True

We can also replace builtin consensual.raft.communication communication layer with another one (like consensual_http which is built on top of HTTP), usage patterns may change as a result.

Development

Bumping version

Preparation

Install bump2version.

Pre-release

Choose which version number category to bump following semver specification.

Test bumping version

bump2version --dry-run --verbose $CATEGORY

where $CATEGORY is the target version number category name, possible values are patch/minor/major.

Bump version

bump2version --verbose $CATEGORY

This will set version to major.minor.patch-alpha.

Release

Test bumping version

bump2version --dry-run --verbose release

Bump version

bump2version --verbose release

This will set version to major.minor.patch.

Running tests

Install dependencies

python -m pip install -r requirements-tests.txt

Plain

pytest

Inside Docker container:

docker-compose --file docker-compose.yml up

Bash script:

./run-tests.sh

PowerShell script:

.\run-tests.ps1