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TLA+ specifications for Raft, including membership changes

This repository contains a number of TLA+ specifications of the Raft consensus protocol. Of particular interest are the following:

• tlc_membership -- a version of Raft with one-at-a-time membership changes (as described in Ongaro's PhD disseration). This includes a few "interesting" scenarios (properties) which can be passes to TLC to generate long traces via "punctuated search".

• apalache_no_membership -- a version of Ricketts' spec with type annotations for the Apalache symbolic model checker. This folder also contains annotated versions of some TLA libraries used in our specification, but does not model membership changes.

The apalache_no_membership spec is known to work with Apalache 0.16.5 build 417cf58.

Original specs

This repository contains specifications adapted by us (George Pîrlea and Darius Foo) from three different existing Raft TLA specifications, which can be found in the thirdparty folder:

• raft_original.tla is the Raft spec published by Diego Ongaro in 2014

• raft_membership.tla is an extension of Ongaro's spec with cluster membership changes, due to Brandom Amos and Huanchen Zhang; they developed it as a course project in 2015

• raft_dricketts.tla is an extension of Ongaro's spec by Daniel Ricketts, developed in 2016; it refactors Ongaro's spec to make it more readable, adds some TLAPS proofs, and states some properties (some of which are incorrect)

Abandoned effort to annotate membership changes

Besides the above, this repository also contains an abandoned effort to add type annotations to the version of the spec that includes membership changes.

• apalache_membership_broken -- an attempt to make the membership version work with (an older version of) Apalache, abandoned after fighting with the type inference algorithm for too long. If you make this work, please let us know by submiting a pull request.

Attribution & Licensing

Our specifications are based on the spec written by Diego Ongaro, with improvements due to Daniel Ricketts, and the addition of cluster membership changes due to Brandon Amos and Huanchen Zhang. We thank them for making these available under a permissive license.

This work is licensed under the Creative Commons Attribution-4.0 International License https://creativecommons.org/licenses/by/4.0/.