1// Copyright 2015 The etcd Authors 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15package raft 16 17import ( 18 "context" 19 "errors" 20 21 pb "go.etcd.io/etcd/raft/raftpb" 22) 23 24type SnapshotStatus int 25 26const ( 27 SnapshotFinish SnapshotStatus = 1 28 SnapshotFailure SnapshotStatus = 2 29) 30 31var ( 32 emptyState = pb.HardState{} 33 34 // ErrStopped is returned by methods on Nodes that have been stopped. 35 ErrStopped = errors.New("raft: stopped") 36) 37 38// SoftState provides state that is useful for logging and debugging. 39// The state is volatile and does not need to be persisted to the WAL. 40type SoftState struct { 41 Lead uint64 // must use atomic operations to access; keep 64-bit aligned. 42 RaftState StateType 43} 44 45func (a *SoftState) equal(b *SoftState) bool { 46 return a.Lead == b.Lead && a.RaftState == b.RaftState 47} 48 49// Ready encapsulates the entries and messages that are ready to read, 50// be saved to stable storage, committed or sent to other peers. 51// All fields in Ready are read-only. 52type Ready struct { 53 // The current volatile state of a Node. 54 // SoftState will be nil if there is no update. 55 // It is not required to consume or store SoftState. 56 *SoftState 57 58 // The current state of a Node to be saved to stable storage BEFORE 59 // Messages are sent. 60 // HardState will be equal to empty state if there is no update. 61 pb.HardState 62 63 // ReadStates can be used for node to serve linearizable read requests locally 64 // when its applied index is greater than the index in ReadState. 65 // Note that the readState will be returned when raft receives msgReadIndex. 66 // The returned is only valid for the request that requested to read. 67 ReadStates []ReadState 68 69 // Entries specifies entries to be saved to stable storage BEFORE 70 // Messages are sent. 71 Entries []pb.Entry 72 73 // Snapshot specifies the snapshot to be saved to stable storage. 74 Snapshot pb.Snapshot 75 76 // CommittedEntries specifies entries to be committed to a 77 // store/state-machine. These have previously been committed to stable 78 // store. 79 CommittedEntries []pb.Entry 80 81 // Messages specifies outbound messages to be sent AFTER Entries are 82 // committed to stable storage. 83 // If it contains a MsgSnap message, the application MUST report back to raft 84 // when the snapshot has been received or has failed by calling ReportSnapshot. 85 Messages []pb.Message 86 87 // MustSync indicates whether the HardState and Entries must be synchronously 88 // written to disk or if an asynchronous write is permissible. 89 MustSync bool 90} 91 92func isHardStateEqual(a, b pb.HardState) bool { 93 return a.Term == b.Term && a.Vote == b.Vote && a.Commit == b.Commit 94} 95 96// IsEmptyHardState returns true if the given HardState is empty. 97func IsEmptyHardState(st pb.HardState) bool { 98 return isHardStateEqual(st, emptyState) 99} 100 101// IsEmptySnap returns true if the given Snapshot is empty. 102func IsEmptySnap(sp pb.Snapshot) bool { 103 return sp.Metadata.Index == 0 104} 105 106func (rd Ready) containsUpdates() bool { 107 return rd.SoftState != nil || !IsEmptyHardState(rd.HardState) || 108 !IsEmptySnap(rd.Snapshot) || len(rd.Entries) > 0 || 109 len(rd.CommittedEntries) > 0 || len(rd.Messages) > 0 || len(rd.ReadStates) != 0 110} 111 112// appliedCursor extracts from the Ready the highest index the client has 113// applied (once the Ready is confirmed via Advance). If no information is 114// contained in the Ready, returns zero. 115func (rd Ready) appliedCursor() uint64 { 116 if n := len(rd.CommittedEntries); n > 0 { 117 return rd.CommittedEntries[n-1].Index 118 } 119 if index := rd.Snapshot.Metadata.Index; index > 0 { 120 return index 121 } 122 return 0 123} 124 125// Node represents a node in a raft cluster. 126type Node interface { 127 // Tick increments the internal logical clock for the Node by a single tick. Election 128 // timeouts and heartbeat timeouts are in units of ticks. 129 Tick() 130 // Campaign causes the Node to transition to candidate state and start campaigning to become leader. 131 Campaign(ctx context.Context) error 132 // Propose proposes that data be appended to the log. Note that proposals can be lost without 133 // notice, therefore it is user's job to ensure proposal retries. 134 Propose(ctx context.Context, data []byte) error 135 // ProposeConfChange proposes a configuration change. Like any proposal, the 136 // configuration change may be dropped with or without an error being 137 // returned. In particular, configuration changes are dropped unless the 138 // leader has certainty that there is no prior unapplied configuration 139 // change in its log. 140 // 141 // The method accepts either a pb.ConfChange (deprecated) or pb.ConfChangeV2 142 // message. The latter allows arbitrary configuration changes via joint 143 // consensus, notably including replacing a voter. Passing a ConfChangeV2 144 // message is only allowed if all Nodes participating in the cluster run a 145 // version of this library aware of the V2 API. See pb.ConfChangeV2 for 146 // usage details and semantics. 147 ProposeConfChange(ctx context.Context, cc pb.ConfChangeI) error 148 149 // Step advances the state machine using the given message. ctx.Err() will be returned, if any. 150 Step(ctx context.Context, msg pb.Message) error 151 152 // Ready returns a channel that returns the current point-in-time state. 153 // Users of the Node must call Advance after retrieving the state returned by Ready. 154 // 155 // NOTE: No committed entries from the next Ready may be applied until all committed entries 156 // and snapshots from the previous one have finished. 157 Ready() <-chan Ready 158 159 // Advance notifies the Node that the application has saved progress up to the last Ready. 160 // It prepares the node to return the next available Ready. 161 // 162 // The application should generally call Advance after it applies the entries in last Ready. 163 // 164 // However, as an optimization, the application may call Advance while it is applying the 165 // commands. For example. when the last Ready contains a snapshot, the application might take 166 // a long time to apply the snapshot data. To continue receiving Ready without blocking raft 167 // progress, it can call Advance before finishing applying the last ready. 168 Advance() 169 // ApplyConfChange applies a config change (previously passed to 170 // ProposeConfChange) to the node. This must be called whenever a config 171 // change is observed in Ready.CommittedEntries. 172 // 173 // Returns an opaque non-nil ConfState protobuf which must be recorded in 174 // snapshots. 175 ApplyConfChange(cc pb.ConfChangeI) *pb.ConfState 176 177 // TransferLeadership attempts to transfer leadership to the given transferee. 178 TransferLeadership(ctx context.Context, lead, transferee uint64) 179 180 // ReadIndex request a read state. The read state will be set in the ready. 181 // Read state has a read index. Once the application advances further than the read 182 // index, any linearizable read requests issued before the read request can be 183 // processed safely. The read state will have the same rctx attached. 184 ReadIndex(ctx context.Context, rctx []byte) error 185 186 // Status returns the current status of the raft state machine. 187 Status() Status 188 // ReportUnreachable reports the given node is not reachable for the last send. 189 ReportUnreachable(id uint64) 190 // ReportSnapshot reports the status of the sent snapshot. The id is the raft ID of the follower 191 // who is meant to receive the snapshot, and the status is SnapshotFinish or SnapshotFailure. 192 // Calling ReportSnapshot with SnapshotFinish is a no-op. But, any failure in applying a 193 // snapshot (for e.g., while streaming it from leader to follower), should be reported to the 194 // leader with SnapshotFailure. When leader sends a snapshot to a follower, it pauses any raft 195 // log probes until the follower can apply the snapshot and advance its state. If the follower 196 // can't do that, for e.g., due to a crash, it could end up in a limbo, never getting any 197 // updates from the leader. Therefore, it is crucial that the application ensures that any 198 // failure in snapshot sending is caught and reported back to the leader; so it can resume raft 199 // log probing in the follower. 200 ReportSnapshot(id uint64, status SnapshotStatus) 201 // Stop performs any necessary termination of the Node. 202 Stop() 203} 204 205type Peer struct { 206 ID uint64 207 Context []byte 208} 209 210// StartNode returns a new Node given configuration and a list of raft peers. 211// It appends a ConfChangeAddNode entry for each given peer to the initial log. 212// 213// Peers must not be zero length; call RestartNode in that case. 214func StartNode(c *Config, peers []Peer) Node { 215 if len(peers) == 0 { 216 panic("no peers given; use RestartNode instead") 217 } 218 rn, err := NewRawNode(c) 219 if err != nil { 220 panic(err) 221 } 222 rn.Bootstrap(peers) 223 224 n := newNode(rn) 225 226 go n.run() 227 return &n 228} 229 230// RestartNode is similar to StartNode but does not take a list of peers. 231// The current membership of the cluster will be restored from the Storage. 232// If the caller has an existing state machine, pass in the last log index that 233// has been applied to it; otherwise use zero. 234func RestartNode(c *Config) Node { 235 rn, err := NewRawNode(c) 236 if err != nil { 237 panic(err) 238 } 239 n := newNode(rn) 240 go n.run() 241 return &n 242} 243 244type msgWithResult struct { 245 m pb.Message 246 result chan error 247} 248 249// node is the canonical implementation of the Node interface 250type node struct { 251 propc chan msgWithResult 252 recvc chan pb.Message 253 confc chan pb.ConfChangeV2 254 confstatec chan pb.ConfState 255 readyc chan Ready 256 advancec chan struct{} 257 tickc chan struct{} 258 done chan struct{} 259 stop chan struct{} 260 status chan chan Status 261 262 rn *RawNode 263} 264 265func newNode(rn *RawNode) node { 266 return node{ 267 propc: make(chan msgWithResult), 268 recvc: make(chan pb.Message), 269 confc: make(chan pb.ConfChangeV2), 270 confstatec: make(chan pb.ConfState), 271 readyc: make(chan Ready), 272 advancec: make(chan struct{}), 273 // make tickc a buffered chan, so raft node can buffer some ticks when the node 274 // is busy processing raft messages. Raft node will resume process buffered 275 // ticks when it becomes idle. 276 tickc: make(chan struct{}, 128), 277 done: make(chan struct{}), 278 stop: make(chan struct{}), 279 status: make(chan chan Status), 280 rn: rn, 281 } 282} 283 284func (n *node) Stop() { 285 select { 286 case n.stop <- struct{}{}: 287 // Not already stopped, so trigger it 288 case <-n.done: 289 // Node has already been stopped - no need to do anything 290 return 291 } 292 // Block until the stop has been acknowledged by run() 293 <-n.done 294} 295 296func (n *node) run() { 297 var propc chan msgWithResult 298 var readyc chan Ready 299 var advancec chan struct{} 300 var rd Ready 301 302 r := n.rn.raft 303 304 lead := None 305 306 for { 307 if advancec != nil { 308 readyc = nil 309 } else if n.rn.HasReady() { 310 // Populate a Ready. Note that this Ready is not guaranteed to 311 // actually be handled. We will arm readyc, but there's no guarantee 312 // that we will actually send on it. It's possible that we will 313 // service another channel instead, loop around, and then populate 314 // the Ready again. We could instead force the previous Ready to be 315 // handled first, but it's generally good to emit larger Readys plus 316 // it simplifies testing (by emitting less frequently and more 317 // predictably). 318 rd = n.rn.readyWithoutAccept() 319 readyc = n.readyc 320 } 321 322 if lead != r.lead { 323 if r.hasLeader() { 324 if lead == None { 325 r.logger.Infof("raft.node: %x elected leader %x at term %d", r.id, r.lead, r.Term) 326 } else { 327 r.logger.Infof("raft.node: %x changed leader from %x to %x at term %d", r.id, lead, r.lead, r.Term) 328 } 329 propc = n.propc 330 } else { 331 r.logger.Infof("raft.node: %x lost leader %x at term %d", r.id, lead, r.Term) 332 propc = nil 333 } 334 lead = r.lead 335 } 336 337 select { 338 // TODO: maybe buffer the config propose if there exists one (the way 339 // described in raft dissertation) 340 // Currently it is dropped in Step silently. 341 case pm := <-propc: 342 m := pm.m 343 m.From = r.id 344 err := r.Step(m) 345 if pm.result != nil { 346 pm.result <- err 347 close(pm.result) 348 } 349 case m := <-n.recvc: 350 // filter out response message from unknown From. 351 if pr := r.prs.Progress[m.From]; pr != nil || !IsResponseMsg(m.Type) { 352 r.Step(m) 353 } 354 case cc := <-n.confc: 355 _, okBefore := r.prs.Progress[r.id] 356 cs := r.applyConfChange(cc) 357 // If the node was removed, block incoming proposals. Note that we 358 // only do this if the node was in the config before. Nodes may be 359 // a member of the group without knowing this (when they're catching 360 // up on the log and don't have the latest config) and we don't want 361 // to block the proposal channel in that case. 362 // 363 // NB: propc is reset when the leader changes, which, if we learn 364 // about it, sort of implies that we got readded, maybe? This isn't 365 // very sound and likely has bugs. 366 if _, okAfter := r.prs.Progress[r.id]; okBefore && !okAfter { 367 var found bool 368 for _, sl := range [][]uint64{cs.Voters, cs.VotersOutgoing} { 369 for _, id := range sl { 370 if id == r.id { 371 found = true 372 } 373 } 374 } 375 if !found { 376 propc = nil 377 } 378 } 379 select { 380 case n.confstatec <- cs: 381 case <-n.done: 382 } 383 case <-n.tickc: 384 n.rn.Tick() 385 case readyc <- rd: 386 n.rn.acceptReady(rd) 387 advancec = n.advancec 388 case <-advancec: 389 n.rn.Advance(rd) 390 rd = Ready{} 391 advancec = nil 392 case c := <-n.status: 393 c <- getStatus(r) 394 case <-n.stop: 395 close(n.done) 396 return 397 } 398 } 399} 400 401// Tick increments the internal logical clock for this Node. Election timeouts 402// and heartbeat timeouts are in units of ticks. 403func (n *node) Tick() { 404 select { 405 case n.tickc <- struct{}{}: 406 case <-n.done: 407 default: 408 n.rn.raft.logger.Warningf("%x (leader %v) A tick missed to fire. Node blocks too long!", n.rn.raft.id, n.rn.raft.id == n.rn.raft.lead) 409 } 410} 411 412func (n *node) Campaign(ctx context.Context) error { return n.step(ctx, pb.Message{Type: pb.MsgHup}) } 413 414func (n *node) Propose(ctx context.Context, data []byte) error { 415 return n.stepWait(ctx, pb.Message{Type: pb.MsgProp, Entries: []pb.Entry{{Data: data}}}) 416} 417 418func (n *node) Step(ctx context.Context, m pb.Message) error { 419 // ignore unexpected local messages receiving over network 420 if IsLocalMsg(m.Type) { 421 // TODO: return an error? 422 return nil 423 } 424 return n.step(ctx, m) 425} 426 427func confChangeToMsg(c pb.ConfChangeI) (pb.Message, error) { 428 typ, data, err := pb.MarshalConfChange(c) 429 if err != nil { 430 return pb.Message{}, err 431 } 432 return pb.Message{Type: pb.MsgProp, Entries: []pb.Entry{{Type: typ, Data: data}}}, nil 433} 434 435func (n *node) ProposeConfChange(ctx context.Context, cc pb.ConfChangeI) error { 436 msg, err := confChangeToMsg(cc) 437 if err != nil { 438 return err 439 } 440 return n.Step(ctx, msg) 441} 442 443func (n *node) step(ctx context.Context, m pb.Message) error { 444 return n.stepWithWaitOption(ctx, m, false) 445} 446 447func (n *node) stepWait(ctx context.Context, m pb.Message) error { 448 return n.stepWithWaitOption(ctx, m, true) 449} 450 451// Step advances the state machine using msgs. The ctx.Err() will be returned, 452// if any. 453func (n *node) stepWithWaitOption(ctx context.Context, m pb.Message, wait bool) error { 454 if m.Type != pb.MsgProp { 455 select { 456 case n.recvc <- m: 457 return nil 458 case <-ctx.Done(): 459 return ctx.Err() 460 case <-n.done: 461 return ErrStopped 462 } 463 } 464 ch := n.propc 465 pm := msgWithResult{m: m} 466 if wait { 467 pm.result = make(chan error, 1) 468 } 469 select { 470 case ch <- pm: 471 if !wait { 472 return nil 473 } 474 case <-ctx.Done(): 475 return ctx.Err() 476 case <-n.done: 477 return ErrStopped 478 } 479 select { 480 case err := <-pm.result: 481 if err != nil { 482 return err 483 } 484 case <-ctx.Done(): 485 return ctx.Err() 486 case <-n.done: 487 return ErrStopped 488 } 489 return nil 490} 491 492func (n *node) Ready() <-chan Ready { return n.readyc } 493 494func (n *node) Advance() { 495 select { 496 case n.advancec <- struct{}{}: 497 case <-n.done: 498 } 499} 500 501func (n *node) ApplyConfChange(cc pb.ConfChangeI) *pb.ConfState { 502 var cs pb.ConfState 503 select { 504 case n.confc <- cc.AsV2(): 505 case <-n.done: 506 } 507 select { 508 case cs = <-n.confstatec: 509 case <-n.done: 510 } 511 return &cs 512} 513 514func (n *node) Status() Status { 515 c := make(chan Status) 516 select { 517 case n.status <- c: 518 return <-c 519 case <-n.done: 520 return Status{} 521 } 522} 523 524func (n *node) ReportUnreachable(id uint64) { 525 select { 526 case n.recvc <- pb.Message{Type: pb.MsgUnreachable, From: id}: 527 case <-n.done: 528 } 529} 530 531func (n *node) ReportSnapshot(id uint64, status SnapshotStatus) { 532 rej := status == SnapshotFailure 533 534 select { 535 case n.recvc <- pb.Message{Type: pb.MsgSnapStatus, From: id, Reject: rej}: 536 case <-n.done: 537 } 538} 539 540func (n *node) TransferLeadership(ctx context.Context, lead, transferee uint64) { 541 select { 542 // manually set 'from' and 'to', so that leader can voluntarily transfers its leadership 543 case n.recvc <- pb.Message{Type: pb.MsgTransferLeader, From: transferee, To: lead}: 544 case <-n.done: 545 case <-ctx.Done(): 546 } 547} 548 549func (n *node) ReadIndex(ctx context.Context, rctx []byte) error { 550 return n.step(ctx, pb.Message{Type: pb.MsgReadIndex, Entries: []pb.Entry{{Data: rctx}}}) 551} 552 553func newReady(r *raft, prevSoftSt *SoftState, prevHardSt pb.HardState) Ready { 554 rd := Ready{ 555 Entries: r.raftLog.unstableEntries(), 556 CommittedEntries: r.raftLog.nextEnts(), 557 Messages: r.msgs, 558 } 559 if softSt := r.softState(); !softSt.equal(prevSoftSt) { 560 rd.SoftState = softSt 561 } 562 if hardSt := r.hardState(); !isHardStateEqual(hardSt, prevHardSt) { 563 rd.HardState = hardSt 564 } 565 if r.raftLog.unstable.snapshot != nil { 566 rd.Snapshot = *r.raftLog.unstable.snapshot 567 } 568 if len(r.readStates) != 0 { 569 rd.ReadStates = r.readStates 570 } 571 rd.MustSync = MustSync(r.hardState(), prevHardSt, len(rd.Entries)) 572 return rd 573} 574 575// MustSync returns true if the hard state and count of Raft entries indicate 576// that a synchronous write to persistent storage is required. 577func MustSync(st, prevst pb.HardState, entsnum int) bool { 578 // Persistent state on all servers: 579 // (Updated on stable storage before responding to RPCs) 580 // currentTerm 581 // votedFor 582 // log entries[] 583 return entsnum != 0 || st.Vote != prevst.Vote || st.Term != prevst.Term 584} 585