手撸golang etcd raft协议之9,10

Posted 2021-09-15 ioly

手撸golang etcd raft协议之9,10

缘起

最近阅读 [云原生分布式存储基石：etcd深入解析] (杜军 , 2019.1)
本系列笔记拟采用golang练习之

raft分布式一致性算法

分布式存储系统通常会通过维护多个副本来进行容错，
以提高系统的可用性。
这就引出了分布式存储系统的核心问题——如何保证多个副本的一致性？

Raft算法把问题分解成了四个子问题：
1. 领袖选举（leader election）、
2. 日志复制（log replication）、
3. 安全性（safety）
4. 成员关系变化（membership changes）
这几个子问题。

源码gitee地址：
https://gitee.com/ioly/learning.gooop

目标

• 根据raft协议，实现高可用分布式强一致的kv存储

子目标（Day 10）

• 添加put/get/del kv键值对的rpc接口
• 继续完善Leader状态的raft协议响应

设计

• rpc/IKVStoreRPC: kv操作的rpc接口
• store/IKVStore: kv操作的持久化接口
• stoer/ILogStore: 从IKVStore继承，以支持kv持久化
• lsm/IRaftState: 继承rpc.IKVStoreRPC接口，以支持kv操作
• lsm/tLeaderState: 初步实现Leader状态的raft协议处理，事件驱动的逻辑编排，读写分离的字段管理。

rpc/IKVStoreRPC.go

kv操作的rpc接口

package rpc

type IKVStoreRPC interface {
    ExecuteKVCmd(cmd *KVCmd, ret *KVRet) error
}

type KVCmd struct {
    OPCode KVOPCode
    Key []byte
    Content []byte
}

type KVOPCode int
const (
    KVGet KVOPCode = iota
    KVPut KVOPCode = iota
    KVDel KVOPCode = iota
)

type KVRet struct {
    Code KVRetCode
    Key []byte
    Content []byte
}

type KVRetCode int
const (
    KVOk KVRetCode = iota
    KVKeyNotFound KVRetCode = iota
    KVInternalError KVRetCode = iota
)

store/IKVStore.go

kv操作的持久化接口

package store

type IKVStore interface {
    Get(key []byte) (error, []byte)
    Put(key []byte, content []byte) error
    Del(key []byte) error
}

stoer/ILogStore.go

从IKVStore继承，以支持kv持久化

package store

import (
    "learning/gooop/etcd/raft/model"
)

type ILogStore interface {
    IKVStore

    LastAppendedTerm() int64
    LastAppendedIndex() int64
    LastCommittedTerm() int64
    LastCommittedIndex() int64

    Append(entry *model.LogEntry) error
    Commit(index int64) error
    GetLog(index int64) (error, *model.LogEntry)
}

lsm/IRaftState.go

继承rpc.IKVStoreRPC接口，以支持kv操作

package lsm

import (
    "learning/gooop/etcd/raft/roles"
    "learning/gooop/etcd/raft/rpc"
)

type IRaftState interface {
    rpc.IRaftRPC
    rpc.IKVStoreRPC

    Role() roles.RaftRole
    Start()
}

lsm/tLeaderState.go

初步实现Leader状态的raft协议处理，事件驱动的逻辑编排，读写分离的字段管理。

package lsm

import (
    "errors"
    "learning/gooop/etcd/raft/config"
    "learning/gooop/etcd/raft/model"
    "learning/gooop/etcd/raft/roles"
    "learning/gooop/etcd/raft/rpc"
    "learning/gooop/etcd/raft/store"
    "learning/gooop/etcd/raft/timeout"
    "sync"
    "time"
)

// tLeaderState presents a leader node
type tLeaderState struct {
    tEventDrivenModel

    context    iRaftStateContext
    mInitOnce  sync.Once
    mStartOnce sync.Once

    // update: leInit / leLeaderHeartbeat
    mTerm int64

    // update: leInit / leDisposing
    mDisposedFlag bool

    // update: leVoteToCandidate
    mVotedTerm int64
    mVotedCandidateID string
    mVotedTimestamp int64
}

// trigger: init()
// args: empty
const leInit = "leader.init"

// trigger: Start()
// args: empty
const leStart = "leader.Start"

// trigger: whenNewLeaderAnnouncedThenSwitchToFollower
// args: empty
const leDiposing = "leader.Disposing"

// trigger : Heartbeat() / AppendLog()
// args: term int64
const leNewLeaderAnnounced = "leader.NewLeaderAnnounced"


// trigger: RequestVote()
// args: *rpc.RequestVoteCmd
const leBeforeRequestVote = "leader.BeforeRequestVote"

// trigger:
// args: *rpc.RequestVoteCmd
const leVoteToCandidate = "leader.VoteToCandidate"

// trigger: handleHeartbeat()
// args: term int64
const leHeartbeatRejected = "leader.HeartbeatRejected"


func newLeaderState(ctx iRaftStateContext, term int64) IRaftState {
    it := new(tLeaderState)
    it.init(ctx, term)
    return it
}

func (me *tLeaderState) init(ctx iRaftStateContext, term int64) {
    me.mInitOnce.Do(func() {
        me.context = ctx
        me.mTerm = term

        me.initEventHandlers()
        me.raise(leInit)
    })
}

func (me *tLeaderState) initEventHandlers() {
    // write only logic
    me.hookEventsForDisposedFlag()
    me.hookEventsForVotedTerm()

    // read only logic
    me.hook(leStart,
        me.whenStartThenBeginHeartbeatToOthers)
    me.hook(leNewLeaderAnnounced,
        me.whenNewLeaderAnnouncedThenSwitchToFollower)
    me.hook(leHeartbeatRejected,
        me.whenHeartbeatRejectedThenSwitchToFollower)
}


func (me *tLeaderState) hookEventsForDisposedFlag() {
    me.hook(leInit, func(e string, args ...interface{}) {
        me.mDisposedFlag = false
    })

    me.hook(leDiposing, func(e string, args ...interface{}) {
        me.mDisposedFlag = true
    })
}

func (me *tLeaderState) hookEventsForVotedTerm() {
    me.hook(leBeforeRequestVote, func(e string, args ...interface{}) {
        // check last vote timeout
        if me.mVotedTerm == 0 {
            return
        }

        if time.Duration(time.Now().UnixNano() - me.mVotedTimestamp)*time.Nanosecond >= timeout.ElectionTimeout {
            me.mVotedTerm = 0
            me.mVotedTimestamp = 0
            me.mVotedCandidateID = ""
        }
    })

    me.hook(leVoteToCandidate, func(e string, args ...interface{}) {
        // after vote to candidate
        cmd := args[0].(*rpc.RequestVoteCmd)
        me.mVotedTerm = cmd.Term
        me.mVotedCandidateID = cmd.CandidateID
        me.mVotedTimestamp = time.Now().UnixNano()
    })
}



func (me *tLeaderState) Heartbeat(cmd *rpc.HeartbeatCmd, ret *rpc.HeartbeatRet) error {
    // check term
    if cmd.Term <= me.mTerm {
        ret.Code = rpc.HBTermMismatch
        return nil
    }

    // new leader
    me.raise(leNewLeaderAnnounced, cmd.Term)

    // return ok
    ret.Code = rpc.HBOk
    return nil
}

func (me *tLeaderState) AppendLog(cmd *rpc.AppendLogCmd, ret *rpc.AppendLogRet) error {
    // check term
    if cmd.Term <= me.mTerm {
        ret.Code = rpc.ALTermMismatch
        return nil
    }

    // new leader
    me.raise(leNewLeaderAnnounced, cmd.Term)

    // return ok
    ret.Code = rpc.ALInternalError
    return nil
}

func (me *tLeaderState) CommitLog(cmd *rpc.CommitLogCmd, ret *rpc.CommitLogRet) error {
    // just ignore
    ret.Code = rpc.CLInternalError
    return nil
}

func (me *tLeaderState) RequestVote(cmd *rpc.RequestVoteCmd, ret *rpc.RequestVoteRet) error {
    me.raise(leBeforeRequestVote, cmd)

    // check voted term
    if cmd.Term < me.mVotedTerm {
        ret.Code = rpc.RVTermMismatch
        return nil
    }

    if cmd.Term == me.mVotedTerm {
        if me.mVotedCandidateID != "" && me.mVotedCandidateID != cmd.CandidateID {
            // already vote another
            ret.Code = rpc.RVVotedAnother
            return nil
        } else {
            // already voted
            ret.Code = rpc.RVOk
            return nil
        }
    }

    if cmd.Term > me.mVotedTerm {
        // new term, check log
        if cmd.LastLogIndex >= me.context.Store().LastCommittedIndex() {
            // good log
            me.raise(leVoteToCandidate, cmd)
            ret.Code = rpc.RVOk

        } else {
            // bad log
            ret.Code = rpc.RVLogMismatch
        }

        return nil
    }

    // should not reach here
    ret.Code = rpc.RVTermMismatch
    return nil
}

func (me *tLeaderState) Role() roles.RaftRole {
    return roles.Leader
}

func (me *tLeaderState) Start() {
    me.mStartOnce.Do(func() {
        me.raise(leStart)
    })
}

func (me *tLeaderState) whenStartThenBeginHeartbeatToOthers(_ string, _ ...interface{}) {
    go func() {
        for !me.mDisposedFlag {
            _ = me.boardcast(func(_ config.IRaftNodeConfig, client rpc.IRaftRPC) error {
                return me.handleHeartbeat(client)
            })
            time.Sleep(timeout.HeartbeatInterval)
        }
    }()
}


func (me *tLeaderState) boardcast(action func(config.IRaftNodeConfig, rpc.IRaftRPC) error) error {
    for _,it := range me.context.Config().Nodes() {
        if it.ID() == me.context.Config().ID() {
            continue
        }

        e := me.context.RaftClientService().Using(it.ID(), func(client rpc.IRaftRPC) error {
            return action(it, client)
        })
        if e != nil {
            return e
        }
    }

    return nil
}


func (me *tLeaderState) handleHeartbeat(client rpc.IRaftRPC) error {
    cmd := new(rpc.HeartbeatCmd)
    cmd.Term = me.mTerm
    cmd.LeaderID = me.context.Config().ID()

    ret := new(rpc.HeartbeatRet)
    e := client.Heartbeat(cmd, ret)
    if e != nil {
        return e
    }

    switch ret.Code {
    case rpc.HBTermMismatch:
        me.raise(leHeartbeatRejected, ret.Term)
        break
    }

    return nil
}

func (me *tLeaderState) whenNewLeaderAnnouncedThenSwitchToFollower(_ string, args ...interface{}) {
    me.raise(leDiposing)

    term := args[0].(int64)
    me.context.HandleStateChanged(newFollowerState(me.context, term))
}

func (me *tLeaderState) whenHeartbeatRejectedThenSwitchToFollower(_ string, args ...interface{}) {
    me.raise(leDiposing)

    term := args[0].(int64)
    me.context.HandleStateChanged(newFollowerState(me.context, term))
}


func (me *tLeaderState) ExecuteKVCmd(cmd *rpc.KVCmd, ret *rpc.KVRet) error {
    switch cmd.OPCode {
    case rpc.KVGet:
        return me.handleKVGet(cmd, ret)

    case rpc.KVPut:
        return me.handleKVPut(cmd, ret)

    case rpc.KVDel:
        return me.handleKVDel(cmd, ret)
    }

    return nil
}

func (me *tLeaderState) handleKVGet(cmd *rpc.KVCmd, ret *rpc.KVRet) error {
    e, v := me.context.Store().Get(cmd.Key)
    if e != nil {
        ret.Code = rpc.KVInternalError
        return e
    }

    ret.Code = rpc.KVOk
    ret.Content = v
    return nil
}

func (me *tLeaderState) handleKVPut(cmd *rpc.KVCmd, ret *rpc.KVRet) error {
    kvcmd := new(store.PutCmd)
    kvcmd.Key = cmd.Key
    kvcmd.Value = cmd.Content

    // create/append/commit log
    e := me.broadcastKVCmd(kvcmd, ret)
    if e != nil {
        return e
    }

    // apply cmd
    return me.context.Store().Put(cmd.Key, cmd.Content)
}

func (me *tLeaderState) handleKVDel(cmd *rpc.KVCmd, ret *rpc.KVRet) error {
    kvcmd := new(store.DelCmd)
    kvcmd.Key = cmd.Key

    // create/append/commit log
    e := me.broadcastKVCmd(kvcmd, ret)
    if e != nil {
        return e
    }

    // apply cmd
    return me.context.Store().Put(cmd.Key, cmd.Content)
}

func (me *tLeaderState) broadcastKVCmd(cmd store.IKVCmd, ret *rpc.KVRet) error {
    // create log
    st := me.context.Store()
    log := new(model.LogEntry)
    log.Term = me.mTerm
    log.Index = st.LastCommittedIndex() + 1
    log.PrevTerm = st.LastCommittedTerm()
    log.PrevIndex = st.LastCommittedIndex()
    log.Command = cmd.Marshal()

    // append log
    e := st.Append(log)
    if e != nil {
        ret.Code = rpc.KVInternalError
        return e
    }

    // ask other nodes to append log
    alcmd := new(rpc.AppendLogCmd)
    alcmd.Term = me.mTerm
    alcmd.LeaderID = me.context.Config().ID()
    alcmd.Entry = log

    sumOk := []int{ 0 }
    _ = me.boardcast(func(_ config.IRaftNodeConfig, client rpc.IRaftRPC) error {
        alret := new(rpc.AppendLogRet)
        e := client.AppendLog(alcmd, alret)
        if e != nil {
            return e
        }

        switch alret.Code {
        case rpc.ALOk:
            sumOk[0]++
            break

        case rpc.ALTermMismatch:
            // todo: fixme
            break

        case rpc.ALIndexMismatch:
            // todo: fixme
            break
        }

        return nil
    })

    // wait for most nodes
    if sumOk[0] >= len(me.context.Config().Nodes()) / 2 {
        // commit log
        clcmd := new(rpc.CommitLogCmd)
        clcmd.LeaderID = me.context.Config().ID()
        clcmd.Term = me.mTerm
        clcmd.Index = log.Index

        _ = me.boardcast(func(_ config.IRaftNodeConfig, client rpc.IRaftRPC) error {
            ret := new(rpc.CommitLogRet)
            e := client.CommitLog(clcmd, ret)
            if e != nil {
                return e
            }

            switch ret.Code {
            case rpc.CLInternalError:
                // todo: fixme
                break

            case rpc.CLLogNotFound:
                // todo: fixme
                break

            case rpc.CLOk:
                return nil
            }

            return nil
        })

        // ok
        return nil

    } else {
        return gErrorCannotReachAgreement
    }
}

var gErrorCannotReachAgreement = errors.New("cannot reach agreement")

（未完待续）