Changelog for raft

0.5.0.0

• Feature: Client write requests are now validated by the leader before being written to its log using the functions from the RaftStateMachine and RaftStateMachinePure typeclasses; Followers do not re-validate the log entry when they receive the entry from the leader.

• Feature: Add nix-build and nix-shell support for use with the nix package manager.

• API change: Added a client request to query a raft node's metrics.

• API change: Added preprocessCmd function to the RaftStateMachine typeclass for implementations where the leader should add data to state machine commands before creating the log entry.

• API change: The clientSendX family of functions now take a ClientReq value as an argument instead of a fully formed ClientRequest value, such that the known ClientId is used to construct the ClientRequest value instead of users having to supply it themselves.

• API change: The RaftStateMachinePureError sm v type family from the RaftStateMachinePure typeclass must now have both a Show and a Serialize instance.

• API change: Client write requests now have the potential of returning a ClientWriteRespFail signifying a failure during the validation of the request state machine update.

• API change: The RaftStateMachine typeclass now has a function preprocessCmd for applications that need the leader to manipulate the command before it is made into a log entry and applied to the state machine.

• Tests: Factor out common test functionality and reorganize test files.

• Tests: Added more comprehensive concurrency tests.

• Bug Fix: When running networks of size 2, 'incrCommitIndex' will no longer run in an infinite loop when incrementing the leader's commit to the correct N.

• Bug Fix: When an invalid client request is submitted, the leader appropriately responds with a failure response and handles the next event as expected.

• Bug Fix: Correctly construct the Append Entries RPC data when handling a client read request as the leader.

• Bug Fix: Candidates now transition to followers if the term in an Append Entries RPC is >= to their current term.

0.4.1.0

• Improvement: Users can now supply an existing logging function to log internal raft node logs, useful for integration into existing applications.
• Improvement: The example instances for RaftClientSend and RaftClientRecv using unix sockets no longer need to fork a server to handle responses from the raft node; the response is sent on the same socket the client opens while sending the request.

0.4.0.0

• API change: MonadRaftAsync is now MonadRaftFork, with a simpler API

0.3.0.0

• API change: runRaftNode now requires the monad it runs in to provide an instance of the MonadRaftAsync and MonadRaftChan in the Raft.Monad module in lieu of the previously necessary MonadConc instance.
• API change: Removed the MonadConc constraint on all example monad transformers and implemented inherited MonadRaftChan and MonadRaftAsync instances
• API change: Removed the MonadConc const
• API change: Renamed the old Raft.Monad module to Raft.Transtion and moved the RaftT monad transformer from Raft.hs to the Raft.Monad module
• Improvement: Rework example monad RaftExampleT for simplicity

0.2.0.0

• Feature: Client requests are now cached by the current leader such that duplicate client requests are not serviced
• Bug Fix: Fix issue in concurrent timer not resetting properly when the timeout was set to values under 500ms
• Feature: Client read requests can now query entries by index or range of indices
• Improvement: Raft nodes now only write to disk if the state changes during handling of events
• Feature: Users can now specify what severity of log messages should be logged
• Bug Fix: Receiving all data from a socket in the RaftSocketT monad transformer RaftRecvX typeclass instances inducing a deadlock has been rewritten
• Feature: A PostgreSQL backend has been added for storage of log entries

0.1.2.0

• Added a heartbeat broadcast by leader on read requests from client to ensure that the node is leader before responding to client
• Each log entry is now linked by sha256 hash to the log entry immediately preceding it
• Fixed bug where the last log entry was not being read from disk before starting the main event loop
• Added quickcheck-state-machine tests for black-box testing of the raft-example client program

0.1.1.0

• Fixed MonadFail constraints for GHC 8.6

0.1.0.0

• Initial release.