Swarmkit筆記（10）——manager處理session請求

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處理session請求是通過_Dispatcher_Session_Handler這個函數（./api/dispatcher.pb.go）：

func _Dispatcher_Session_Handler(srv interface{}, stream grpc.ServerStream) error {    m := new(SessionRequest)    if err := stream.RecvMsg(m); err != nil {        return err    }    return srv.(DispatcherServer).Session(m, &dispatcherSessionServer{stream})}

實際函數調用棧如下：

0  0x0000000000b65cbf in github.com/docker/swarmkit/manager/dispatcher.(*Dispatcher).Session   at /go/src/github.com/docker/swarmkit/manager/dispatcher/dispatcher.go:7681  0x0000000000782aa5 in github.com/docker/swarmkit/api.(*authenticatedWrapperDispatcherServer).Session   at /go/src/github.com/docker/swarmkit/api/dispatcher.pb.go:2072  0x000000000078e505 in github.com/docker/swarmkit/api.(*raftProxyDispatcherServer).Session   at /go/src/github.com/docker/swarmkit/api/dispatcher.pb.go:11213  0x0000000000789c2a in github.com/docker/swarmkit/api._Dispatcher_Session_Handler   at /go/src/github.com/docker/swarmkit/api/dispatcher.pb.go:6674  0x0000000000909646 in github.com/docker/swarmkit/vendor/google.golang.org/grpc.(*Server).processStreamingRPC   at /go/src/github.com/docker/swarmkit/vendor/google.golang.org/grpc/server.go:6025  0x000000000090b002 in github.com/docker/swarmkit/vendor/google.golang.org/grpc.(*Server).handleStream   at /go/src/github.com/docker/swarmkit/vendor/google.golang.org/grpc/server.go:6866  0x000000000090fcbe in github.com/docker/swarmkit/vendor/google.golang.org/grpc.(*Server).serveStreams.func1.1   at /go/src/github.com/docker/swarmkit/vendor/google.golang.org/grpc/server.go:3487  0x0000000000462bf0 in runtime.goexit   at /usr/local/go/src/runtime/asm_amd64.s:1998

Dispatcher.Session()函數代碼如下：

// Session is a stream which controls agent connection.// Each message contains list of backup Managers with weights. Also there is// a special boolean field Disconnect which if true indicates that node should// reconnect to another Manager immediately.func (d *Dispatcher) Session(r *api.SessionRequest, stream api.Dispatcher_SessionServer) error {    ctx := stream.Context()    nodeInfo, err := ca.RemoteNode(ctx)    if err != nil {        return err    }    nodeID := nodeInfo.NodeID    if err := d.isRunningLocked(); err != nil {        return err    }    // register the node.    sessionID, err := d.register(stream.Context(), nodeID, r.Description)    if err != nil {        return err    }    fields := logrus.Fields{        "node.id":      nodeID,        "node.session": sessionID,        "method":       "(*Dispatcher).Session",    }    if nodeInfo.ForwardedBy != nil {        fields["forwarder.id"] = nodeInfo.ForwardedBy.NodeID    }    log := log.G(ctx).WithFields(fields)    var nodeObj *api.Node    nodeUpdates, cancel, err := store.ViewAndWatch(d.store, func(readTx store.ReadTx) error {        nodeObj = store.GetNode(readTx, nodeID)        return nil    }, state.EventUpdateNode{Node: &api.Node{ID: nodeID},        Checks: []state.NodeCheckFunc{state.NodeCheckID}},    )    if cancel != nil {        defer cancel()    }    if err != nil {        log.WithError(err).Error("ViewAndWatch Node failed")    }    if _, err = d.nodes.GetWithSession(nodeID, sessionID); err != nil {        return err    }    if err := stream.Send(&api.SessionMessage{        SessionID:            sessionID,        Node:                 nodeObj,        Managers:             d.getManagers(),        NetworkBootstrapKeys: d.networkBootstrapKeys,    }); err != nil {        return err    }    managerUpdates, mgrCancel := d.mgrQueue.Watch()    defer mgrCancel()    keyMgrUpdates, keyMgrCancel := d.keyMgrQueue.Watch()    defer keyMgrCancel()    // disconnectNode is a helper forcibly shutdown connection    disconnectNode := func() error {        // force disconnect by shutting down the stream.        transportStream, ok := transport.StreamFromContext(stream.Context())        if ok {            // if we have the transport stream, we can signal a disconnect            // in the client.            if err := transportStream.ServerTransport().Close(); err != nil {                log.WithError(err).Error("session end")            }        }        nodeStatus := api.NodeStatus{State: api.NodeStatus_DISCONNECTED, Message: "node is currently trying to find new manager"}        if err := d.nodeRemove(nodeID, nodeStatus); err != nil {            log.WithError(err).Error("failed to remove node")        }        // still return an abort if the transport closure was ineffective.        return grpc.Errorf(codes.Aborted, "node must disconnect")    }    for {        // After each message send, we need to check the nodes sessionID hasn't        // changed. If it has, we will the stream and make the node        // re-register.        node, err := d.nodes.GetWithSession(nodeID, sessionID)        if err != nil {            return err        }        var mgrs []*api.WeightedPeer        var disconnect bool        select {        case ev := <-managerUpdates:            mgrs = ev.([]*api.WeightedPeer)        case ev := <-nodeUpdates:            nodeObj = ev.(state.EventUpdateNode).Node        case <-stream.Context().Done():            return stream.Context().Err()        case <-node.Disconnect:            disconnect = true        case <-d.ctx.Done():            disconnect = true        case <-keyMgrUpdates:        }        if mgrs == nil {            mgrs = d.getManagers()        }        if err := stream.Send(&api.SessionMessage{            SessionID:            sessionID,            Node:                 nodeObj,            Managers:             mgrs,            NetworkBootstrapKeys: d.networkBootstrapKeys,        }); err != nil {            return err        }        if disconnect {            return disconnectNode()        }    }}

這個stream是處理agent串連的。前半部分是把串連的agent記錄下來；後半部分是如果cluster資訊發送變化，比如manager的leader發生變化，需要通知agent重新串連。disconnectNode()函數則是需要同agent node中斷連線時的處理：包括中斷連線，agent node資訊刪除，等等。