public static bool CheckIfValidLeader(RachisConsensus engine, RemoteConnection connection, out LogLengthNegotiation negotiation)
{
negotiation = null;
using (engine.ContextPool.AllocateOperationContext(out ClusterOperationContext context))
{
var logLength = connection.Read <LogLengthNegotiation>(context);
if (logLength.Term < engine.CurrentTerm)
{
var msg = $"The incoming term {logLength.Term} is smaller than current term {engine.CurrentTerm} and is therefor rejected (From thread: {logLength.SendingThread})";
if (engine.Log.IsInfoEnabled)
{
engine.Log.Info(msg);
}
connection.Send(context, new LogLengthNegotiationResponse
{
Status = LogLengthNegotiationResponse.ResponseStatus.Rejected,
Message = msg,
CurrentTerm = engine.CurrentTerm
});
connection.Dispose();
return(false);
}
if (engine.Log.IsInfoEnabled)
{
engine.Log.Info($"The incoming term { logLength.Term} is from a valid leader (From thread: {logLength.SendingThread})");
}
engine.FoundAboutHigherTerm(logLength.Term, "Setting the term of the new leader");
engine.Timeout.Defer(connection.Source);
negotiation = logLength;
}
return(true);
}
/// <summary>
/// This method may run for a long while, as we are trying to get agreement
/// from a majority of the cluster
/// </summary>
private void Run()
{
try
{
while (_candidate.Running && _disposed == false)
{
try
{
Stream stream;
try
{
using (_engine.ContextPool.AllocateOperationContext(out TransactionOperationContext context))
{
stream = _engine.ConnectToPeer(_url, _certificate, context).Result;
}
if (_candidate.Running == false)
{
break;
}
}
catch (Exception e)
{
Status = AmbassadorStatus.FailedToConnect;
StatusMessage = $"Failed to connect with {_tag}.{Environment.NewLine} " + e.Message;
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"CandidateAmbassador {_engine.Tag}: Failed to connect to remote peer: " + _url, e);
}
// wait a bit
_candidate.WaitForChangeInState();
continue; // we'll retry connecting
}
Status = AmbassadorStatus.Connected;
StatusMessage = $"Connected to {_tag}";
Connection = new RemoteConnection(_tag, _engine.Tag, stream);
using (_engine.ContextPool.AllocateOperationContext(out TransactionOperationContext context))
{
ClusterTopology topology;
long lastLogIndex;
long lastLogTerm;
using (context.OpenReadTransaction())
{
topology = _engine.GetTopology(context);
lastLogIndex = _engine.GetLastEntryIndex(context);
lastLogTerm = _engine.GetTermForKnownExisting(context, lastLogIndex);
}
Debug.Assert(topology.TopologyId != null);
Connection.Send(context, new RachisHello
{
TopologyId = topology.TopologyId,
DebugSourceIdentifier = _engine.Tag,
DebugDestinationIdentifier = _tag,
InitialMessageType = InitialMessageType.RequestVote
});
while (_candidate.Running)
{
RequestVoteResponse rvr;
var currentElectionTerm = _candidate.ElectionTerm;
var engineCurrentTerm = _engine.CurrentTerm;
if (_candidate.IsForcedElection == false ||
_candidate.RunRealElectionAtTerm != currentElectionTerm)
{
Connection.Send(context, new RequestVote
{
Source = _engine.Tag,
Term = currentElectionTerm,
IsForcedElection = false,
IsTrialElection = true,
LastLogIndex = lastLogIndex,
LastLogTerm = lastLogTerm
});
rvr = Connection.Read <RequestVoteResponse>(context);
if (rvr.Term > currentElectionTerm)
{
var message = $"Candidate ambassador {_engine.Tag}: found election term {rvr.Term} that is higher than ours {currentElectionTerm}";
// we need to abort the current elections
_engine.SetNewState(RachisState.Follower, null, engineCurrentTerm, message);
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"CandidateAmbassador {_engine.Tag}: {message}");
}
_engine.FoundAboutHigherTerm(rvr.Term);
throw new InvalidOperationException(message);
}
NotInTopology = rvr.NotInTopology;
if (rvr.VoteGranted == false)
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"CandidateAmbassador {_engine.Tag}: Got a negative response from {_tag} reason: {rvr.Message}");
}
// we go a negative response here, so we can't proceed
// we'll need to wait until the candidate has done something, like
// change term or given up
_candidate.WaitForChangeInState();
continue;
}
TrialElectionWonAtTerm = rvr.Term;
_candidate.WaitForChangeInState();
}
Connection.Send(context, new RequestVote
{
Source = _engine.Tag,
Term = currentElectionTerm,
IsForcedElection = _candidate.IsForcedElection,
IsTrialElection = false,
LastLogIndex = lastLogIndex,
LastLogTerm = lastLogTerm
});
rvr = Connection.Read <RequestVoteResponse>(context);
if (rvr.Term > currentElectionTerm)
{
var message = $"Candidate ambassador {_engine.Tag}: found election term {rvr.Term} that is higher than ours {currentElectionTerm}";
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"CandidateAmbassador {_engine.Tag}: {message}");
}
// we need to abort the current elections
_engine.SetNewState(RachisState.Follower, null, engineCurrentTerm, message);
_engine.FoundAboutHigherTerm(rvr.Term);
throw new InvalidOperationException(message);
}
NotInTopology = rvr.NotInTopology;
if (rvr.VoteGranted == false)
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"CandidateAmbassador {_engine.Tag}: Got a negative response from {_tag} reason: {rvr.Message}");
}
// we go a negative response here, so we can't proceed
// we'll need to wait until the candidate has done something, like
// change term or given up
_candidate.WaitForChangeInState();
continue;
}
RealElectionWonAtTerm = rvr.Term;
_candidate.WaitForChangeInState();
}
SendElectionResult();
}
}
catch (OperationCanceledException)
{
Status = AmbassadorStatus.Closed;
StatusMessage = "Closed";
SendElectionResult();
break;
}
catch (ObjectDisposedException)
{
Status = AmbassadorStatus.Closed;
StatusMessage = "Closed";
SendElectionResult();
break;
}
catch (AggregateException ae)
when(ae.InnerException is OperationCanceledException || ae.InnerException is ObjectDisposedException)
{
Status = AmbassadorStatus.Closed;
StatusMessage = "Closed";
SendElectionResult();
break;
}
catch (Exception e)
{
Status = AmbassadorStatus.FailedToConnect;
StatusMessage = $"Failed to get vote from {_tag}.{Environment.NewLine}" + e.Message;
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"CandidateAmbassador {_engine.Tag}: Failed to get vote from remote peer url={_url} tag={_tag}", e);
}
Connection?.Dispose();
_candidate.WaitForChangeInState();
}
}
}
catch (Exception e)
{
Status = AmbassadorStatus.FailedToConnect;
StatusMessage = $"Failed to talk to {_url}.{Environment.NewLine}" + e;
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info("Failed to talk to remote peer: " + _url, e);
}
}
finally
{
if (_candidate.ElectionResult != ElectionResult.Won)
{
Connection?.Dispose();
}
}
}
private void NegotiateWithLeader(TransactionOperationContext context, LogLengthNegotiation negotiation)
{
// only the leader can send append entries, so if we accepted it, it's the leader
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"Follower {_engine.Tag}: Got a negotiation request for term {negotiation.Term} where our term is {_engine.CurrentTerm}");
}
if (negotiation.Term > _engine.CurrentTerm)
{
_engine.FoundAboutHigherTerm(negotiation.Term);
}
long prevTerm;
using (context.OpenReadTransaction())
{
prevTerm = _engine.GetTermFor(context, negotiation.PrevLogIndex) ?? 0;
}
if (prevTerm != negotiation.PrevLogTerm)
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"Follower {_engine.Tag}: Got a negotiation request with PrevLogTerm={negotiation.PrevLogTerm} while our PrevLogTerm={prevTerm}" +
" will negotiate to find next matched index");
}
// we now have a mismatch with the log position, and need to negotiate it with
// the leader
NegotiateMatchEntryWithLeaderAndApplyEntries(context, _connection, negotiation);
}
else
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"Follower {_engine.Tag}: Got a negotiation request with identical PrevLogTerm will continue to steady state");
}
// this (or the negotiation above) completes the negotiation process
_connection.Send(context, new LogLengthNegotiationResponse
{
Status = LogLengthNegotiationResponse.ResponseStatus.Acceptable,
Message = $"Found a log index / term match at {negotiation.PrevLogIndex} with term {prevTerm}",
CurrentTerm = _engine.CurrentTerm,
LastLogIndex = negotiation.PrevLogIndex
});
}
_engine.Timeout.Defer(_connection.Source);
// at this point, the leader will send us a snapshot message
// in most cases, it is an empty snapshot, then start regular append entries
// the reason we send this is to simplify the # of states in the protocol
var snapshot = _connection.ReadInstallSnapshot(context);
using (context.OpenWriteTransaction())
{
var lastCommitIndex = _engine.GetLastCommitIndex(context);
if (snapshot.LastIncludedIndex < lastCommitIndex)
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info(
$"Follower {_engine.Tag}: Got installed snapshot with last index={snapshot.LastIncludedIndex} while our lastCommitIndex={lastCommitIndex}, will just ignore it");
}
//This is okay to ignore because we will just get the commited entries again and skip them
ReadInstallSnapshotAndIgnoreContent(context);
}
else if (InstallSnapshot(context))
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info(
$"Follower {_engine.Tag}: Installed snapshot with last index={snapshot.LastIncludedIndex} with LastIncludedTerm={snapshot.LastIncludedTerm} ");
}
_engine.SetLastCommitIndex(context, snapshot.LastIncludedIndex, snapshot.LastIncludedTerm);
_engine.ClearLogEntriesAndSetLastTruncate(context, snapshot.LastIncludedIndex, snapshot.LastIncludedTerm);
}
else
{
var lastEntryIndex = _engine.GetLastEntryIndex(context);
if (lastEntryIndex < snapshot.LastIncludedIndex)
{
var message =
$"The snapshot installation had failed because the last included index {snapshot.LastIncludedIndex} in term {snapshot.LastIncludedTerm} doesn't match the last entry {lastEntryIndex}";
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"Follower {_engine.Tag}: {message}");
}
throw new InvalidOperationException(message);
}
}
// snapshot always has the latest topology
if (snapshot.Topology == null)
{
const string message = "Expected to get topology on snapshot";
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"Follower {_engine.Tag}: {message}");
}
throw new InvalidOperationException(message);
}
using (var topologyJson = context.ReadObject(snapshot.Topology, "topology"))
{
if (_engine.Log.IsInfoEnabled)
{
_engine.Log.Info($"Follower {_engine.Tag}: topology on install snapshot: {topologyJson}");
}
var topology = JsonDeserializationRachis <ClusterTopology> .Deserialize(topologyJson);
RachisConsensus.SetTopology(_engine, context, topology);
}
context.Transaction.Commit();
}
//Here we send the LastIncludedIndex as our matched index even for the case where our lastCommitIndex is greater
//So we could validate that the entries sent by the leader are indeed the same as the ones we have.
_connection.Send(context, new InstallSnapshotResponse
{
Done = true,
CurrentTerm = _engine.CurrentTerm,
LastLogIndex = snapshot.LastIncludedIndex
});
_engine.Timeout.Defer(_connection.Source);
// notify the state machine
_engine.SnapshotInstalled(context, snapshot.LastIncludedIndex);
_engine.Timeout.Defer(_connection.Source);
}
