Swarmkit筆記（14）——manager切換角色

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

Manager結構體（定義在manager/manager.go）包含一個*raft.Node成員：

// Manager is the cluster manager for Swarm.// This is the high-level object holding and initializing all the manager// subsystems.type Manager struct {    ......    RaftNode   *raft.Node    ......}

而raft.Node（定義在manager/state/raft/raft.go）則包含一個*events.Broadcaster成員，用來接收改變manager role的訊息（變成leader還是follower）：

// Node represents the Raft Node useful// configuration.type Node struct {    ......    leadershipBroadcast *events.Broadcaster    ......}   

發送改變當前manager role的代碼位於manager/state/raft/raft.go：

// Run is the main loop for a Raft node, it goes along the state machine,// acting on the messages received from other Raft nodes in the cluster.//// Before running the main loop, it first starts the raft node based on saved// cluster state. If no saved state exists, it starts a single-node cluster.func (n *Node) Run(ctx context.Context) error {    ......            // If we cease to be the leader, we must cancel            // any proposals that are currently waiting for            // a quorum to acknowledge them. It is still            // possible for these to become committed, but            // if that happens we will apply them as any            // follower would.            if rd.SoftState != nil {                if wasLeader && rd.SoftState.RaftState != raft.StateLeader {                    wasLeader = false                    n.wait.cancelAll()                    if atomic.LoadUint32(&n.signalledLeadership) == 1 {                        atomic.StoreUint32(&n.signalledLeadership, 0)                        n.leadershipBroadcast.Write(IsFollower)                    }                } else if !wasLeader && rd.SoftState.RaftState == raft.StateLeader {                    wasLeader = true                }            }            if wasLeader && atomic.LoadUint32(&n.signalledLeadership) != 1 {                // If all the entries in the log have become                // committed, broadcast our leadership status.                if n.caughtUp() {                    atomic.StoreUint32(&n.signalledLeadership, 1)                    n.leadershipBroadcast.Write(IsLeader)                }            }    ......}

接收訊息的代碼在Manager.Run()函數（manager/manager.go）:

// Run starts all manager sub-systems and the gRPC server at the configured// address.// The call never returns unless an error occurs or `Stop()` is called.func (m *Manager) Run(parent context.Context) error {    ......    leadershipCh, cancel := m.RaftNode.SubscribeLeadership()    defer cancel()    go m.handleLeadershipEvents(ctx, leadershipCh)    ......    go func() {            err := m.RaftNode.Run(ctx)            if err != nil {                log.G(ctx).Error(err)                m.Stop(ctx)            }        }()    ......}

Node.SubscribeLeadership()和Manager.handleLeadershipEvents()代碼比較簡單，不再贅述。