Python implementation of the Raft algorithm for distributed consensus
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README.md

Zatt

Zatt is a distributed storage system built on the Raft consensus algorithm.

By default, clients share a dict data structure, although every python object is potentially replicable with the pickle state machine.

Zatt was developed as part of my thesis work at the University of Trento, Italy. See Slides and Thesis.

Zatt Logo

Please note that the client is compatible with both python2 and python3, while the server makes heavy use of the asynchronous programming library asyncio and is therefore python3-only. This won't affect compatibility with legacy code since the server is standalone.

Structure of the project

The most relevant part of the code concerning Raft is in the states and in the log files.

TODO: extend

Installing

Both the server and the client are shipped in the same package (Note: this link won't work until the project is public).

Zatt can be installed by several means:

Pypi

$ pip3 install zatt. (Note: this won't work until the project is public).

Pip and Git

$ pip3 install git+ssh://github.com/simonacca/zatt.git@develop

Cloning

$ git clone git@github.com:simonacca/zatt.git
$ cd zatt
$ git checkout develop
$ python3 setup.py install

Regardless of the installation method, $ zattd --help should work at this point.

Examples

This screencast shows a basic usage of the code. The code run can be found below.

asciicast

Spinning up a cluster of servers

A server can be configured with command-line options or with a config file, in this example, we are going to use both.

First, create an empty folder and enter it: $ mkdir zatt_cluster && cd zatt_cluster.

Now create a config file zatt.conf with the following content:

{"cluster": {
    "0": ["127.0.0.1", 5254],
    "1": ["127.0.0.1", 5255],
    "2": ["127.0.0.1", 5256]
 }
}

You can now run the first node:

$ zattd -c zatt.conf --id 0 -s zatt.0.persist --debug

This tells zattd to run the node with id:0, taking the info about address and port from the config file.

Now you can spin up a second node: open another terminal, navigate to zatt_cluster and issue:

$ zattd -c zatt.conf --id 2 -s zatt.2.persist --debug

Repeat for a third node, this time with id:2

Client

To interact with the cluster, we need a client. Open a python interpreter ($ python) and run the following commands:

In [1]: from zatt.client import DistributedDict
In [2]: d = DistributedDict('127.0.0.1', 5254)
In [3]: d['key1'] = 0

Let's retrieve key1 from a second client:

Open the python interpreter on another terminal and run:

In [1]: from zatt.client import DistributedDict
In [2]: d = DistributedDict('127.0.0.1', 5254)
In [3]: d['key1']
Out[3]: 0
In [4]: d
Out[4]: {'key1': 0}

Notes

Please note that in order to erase the log of a node, the corresponding zatt.{id}.persist folder has to be removed.

Also note that JSON, currently used for serialization, only supports keys of type str and values of type int, float, str, bool, list, dict.

Tests

In order to run the tests:

  • clone the repo if you haven't done so already: git clone git@github.com:simonacca/zatt.git
  • navigate to the test folder: cd zatt/tests
  • execute: python3 run.py

Contributing

TODO

License

TODO