Docker Swarm代码分析笔记(15)——scheduler

Docker Swarm manage命令的scheduler是通过filterstrategy构建的(cli/manage.go):

sched := scheduler.New(s, fs)

scheduler实际的功能就是选择符合cluster.ContainerConfig要求的nodeDocker Engine)列表:

// SelectNodesForContainer will return a list of nodes where the container can
// be scheduled, sorted by order or preference.
func (s *Scheduler) SelectNodesForContainer(nodes []*node.Node, config *cluster.ContainerConfig) ([]*node.Node, error) {
    candidates, err := s.selectNodesForContainer(nodes, config, true)

    if err != nil {
        candidates, err = s.selectNodesForContainer(nodes, config, false)
    }
    return candidates, err
}

func (s *Scheduler) selectNodesForContainer(nodes []*node.Node, config *cluster.ContainerConfig, soft bool) ([]*node.Node, error) {
    accepted, err := filter.ApplyFilters(s.filters, config, nodes, soft)
    if err != nil {
        return nil, err
    }

    if len(accepted) == 0 {
        return nil, errNoNodeAvailable
    }

    return s.strategy.RankAndSort(config, accepted)
}

 

Docker Swarm代码分析笔记(14)——strategy

Docker Swarm manage命令的flStrategy选项用来指定scheduler调度的strategy的过滤项,其变量定义如下(cli/flags.go):

flStrategy = cli.StringFlag{
    Name:  "strategy",
    Usage: "placement strategy to use [" + strings.Join(strategy.List(), ", ") + "]",
    Value: strategy.List()[0],
}

strategy的默认值是SpreadPlacementStrategy

strategy在代码中的实际定义是PlacementStrategy,一个interface

// PlacementStrategy is the interface for a container placement strategy.
type PlacementStrategy interface {
    // Name of the strategy
    Name() string
    // Initialize performs any initial configuration required by the strategy and returns
    // an error if one is encountered.
    // If no initial configuration is needed, this may be a no-op and return a nil error.
    Initialize() error
    // RankAndSort applies the strategy to a list of nodes and ranks them based
    // on the best fit given the container configuration.  It returns a sorted
    // list of nodes (based on their ranks) or an error if there is no
    // available node on which to schedule the container.
    RankAndSort(config *cluster.ContainerConfig, nodes []*node.Node) ([]*node.Node, error)
}

其中RankAndSort返回一个符合条件node(也就是Docker Engine)列表,列表中元素按匹配度排序。

Docker Swarm代码分析笔记(13)——filter

Docker Swarm manage命令的filter选项用来指定scheduler选择Docker Engine的过滤项,其变量定义如下(cli/flags.go):

// hack for go vet
flFilterValue = cli.StringSlice(filter.List())
// DefaultFilterNumber is exported
DefaultFilterNumber = len(flFilterValue)

flFilter = cli.StringSliceFlag{
    Name:  "filter, f",
    Usage: "filter to use [" + strings.Join(filter.List(), ", ") + "]",
    Value: &flFilterValue,
}

获得filter值的代码如下(cli/manage.go):

// see https://github.com/codegangsta/cli/issues/160
names := c.StringSlice("filter")
if c.IsSet("filter") || c.IsSet("f") {
    names = names[DefaultFilterNumber:]
}
fs, err := filter.New(names)
if err != nil {
    log.Fatal(err)
}

默认情况下,获得所有的filterscheduler/filter/filter.go):

func init() {
    filters = []Filter{
        &HealthFilter{},
        &PortFilter{},
        &SlotsFilter{},
        &DependencyFilter{},
        &AffinityFilter{},
        &ConstraintFilter{},
    }
}

Filter是一个interfacescheduler/filter/filter.go):

// Filter is exported
type Filter interface {
    Name() string

    // Return a subset of nodes that were accepted by the filtering policy.
    Filter(*cluster.ContainerConfig, []*node.Node, bool) ([]*node.Node, error)

    // Return a list of constraints/filters provided
    GetFilters(*cluster.ContainerConfig) ([]string, error)
}

其中Filter方法用来过滤符合条件的Docker Engine,而GetFilters则返回一个描述过滤条件的字符串。

scheduler/filter/filter.go中,ApplyFilters用来过滤Docker EnginelistAllFilters返回所有的过滤条件:

// ApplyFilters applies a set of filters in batch.
func ApplyFilters(filters []Filter, config *cluster.ContainerConfig, nodes []*node.Node, soft bool) ([]*node.Node, error) {
    var (
        err        error
        candidates = nodes
    )

    for _, filter := range filters {
        candidates, err = filter.Filter(config, candidates, soft)
        if err != nil {
            // special case for when no healthy nodes are found
            if filter.Name() == "health" {
                return nil, err
            }
            return nil, fmt.Errorf("Unable to find a node that satisfies the following conditions %s", listAllFilters(filters, config, filter.Name()))
        }
    }
    return candidates, nil
}

// listAllFilters creates a string containing all applied filters
func listAllFilters(filters []Filter, config *cluster.ContainerConfig, lastFilter string) string {
    allFilters := ""
    for _, filter := range filters {
        list, err := filter.GetFilters(config)
        if err == nil && len(list) > 0 {
            allFilters = fmt.Sprintf("%s\n%v", allFilters, list)
        }
        if filter.Name() == lastFilter {
            return allFilters
        }
    }
    return allFilters
}

 

Docker Swarm代码分析笔记(12)——container相关的config

创建和更新container时需要涉及到containerconfigcluster\config.go):

// ContainerConfig is exported
// TODO store affinities and constraints in their own fields
type ContainerConfig struct {
    container.Config
    HostConfig       container.HostConfig
    NetworkingConfig network.NetworkingConfig
}

// OldContainerConfig contains additional fields for backward compatibility
// This should be removed after we stop supporting API versions <= 1.8
type OldContainerConfig struct {
    ContainerConfig
    Memory     int64
    MemorySwap int64
    CPUShares  int64  `json:"CpuShares"`
    CPUSet     string `json:"Cpuset"`
}

其中container这个package定义在/vendor/github.com/docker/engine-api/types/container/config.gocontainer.Config包含不依赖于hostcontainerconfig;依赖于hostconfig定义在container.HostConfig;而container网络相关的config保存在network.NetworkingConfig

 

Docker Swarm代码分析笔记(11)——Engine.Connect

Engine.Connect()方法用来完成对Docker engine的连接工作:

// Connect will initialize a connection to the Docker daemon running on the
// host, gather machine specs (memory, cpu, ...) and monitor state changes.
func (e *Engine) Connect(config *tls.Config) error {
    host, _, err := net.SplitHostPort(e.Addr)
    if err != nil {
        return err
    }

    addr, err := net.ResolveIPAddr("ip4", host)
    if err != nil {
        return err
    }
    e.IP = addr.IP.String()

    c, err := dockerclient.NewDockerClientTimeout("tcp://"+e.Addr, config, time.Duration(requestTimeout), setTCPUserTimeout)
    if err != nil {
        return err
    }
    // Use HTTP Client used by dockerclient to create engine-api client
    apiClient, err := engineapi.NewClient("tcp://"+e.Addr, "", c.HTTPClient, nil)
    if err != nil {
        return err
    }

    return e.ConnectWithClient(c, apiClient)
}

Engine.Connect()利用了另外两个Docker项目:dockerclientengine-api。首先调用dockerclient.NewDockerClientTimeout("tcp://"+e.Addr, config, time.Duration(requestTimeout), setTCPUserTimeout)生成一个DockerClient结构体:

type DockerClient struct {
    URL           *url.URL
    HTTPClient    *http.Client
    TLSConfig     *tls.Config
    monitorStats  int32
    eventStopChan chan (struct{})
}

再把DockerClient.HTTPClient传入engineapi.NewClient()函数,作为engine-apihttp.Client,作为HTTP请求的传输载体。最后调用Engine.ConnectWithClient()连接Docker engine,获得Docker信息。

 

Docker Swarm代码分析笔记(10)——Cluster.validatePendingEngine

Cluster.validatePendingEngine是实际上用来连接Docker engine的代码:

// validatePendingEngine connects to the engine,
func (c *Cluster) validatePendingEngine(engine *cluster.Engine) bool {
    // Attempt a connection to the engine. Since this is slow, don't get a hold
    // of the lock yet.
    if err := engine.Connect(c.TLSConfig); err != nil {
        log.WithFields(log.Fields{"Addr": engine.Addr}).Debugf("Failed to validate pending node: %s", err)
        return false
    }

    // The following is critical and fast. Grab a lock.
    c.Lock()
    defer c.Unlock()

    // Only validate engines from pendingEngines list
    if _, exists := c.pendingEngines[engine.Addr]; !exists {
        return false
    }

    // Make sure the engine ID is unique.
    if old, exists := c.engines[engine.ID]; exists {
        if old.Addr != engine.Addr {
            log.Errorf("ID duplicated. %s shared by %s and %s", engine.ID, old.Addr, engine.Addr)
            // Keep this engine in pendingEngines table and show its error.
            // If it's ID duplication from VM clone, user see this message and can fix it.
            // If the engine is rebooted and get new IP from DHCP, previous address will be removed
            // from discovery after a while.
            // In both cases, retry may fix the problem.
            engine.HandleIDConflict(old.Addr)
        } else {
            log.Debugf("node %q (name: %q) with address %q is already registered", engine.ID, engine.Name, engine.Addr)
            engine.Disconnect()
            // Remove it from pendingEngines table
            delete(c.pendingEngines, engine.Addr)
        }
        return false
    }

    // Engine validated, move from pendingEngines table to engines table
    delete(c.pendingEngines, engine.Addr)
    // set engine state to healthy, and start refresh loop
    engine.ValidationComplete()
    c.engines[engine.ID] = engine

    log.Infof("Registered Engine %s at %s", engine.Name, engine.Addr)
    return true
}

Cluster.validatePendingEngine永远操作Cluster.pendingEngines里的Engine,如果连接Docker engine成功,就会把这个Engine移到Cluster.engines这个map里。

 

Docker Swarm代码分析笔记(9)——Swarm的Cluster,Engine和addEngine

swarm/cluster.go属于swarm这个package,它定义了swarm这个driverCluster结构体:

// Cluster is exported
type Cluster struct {
    sync.RWMutex

    eventHandlers     *cluster.EventHandlers
    engines           map[string]*cluster.Engine
    pendingEngines    map[string]*cluster.Engine
    scheduler         *scheduler.Scheduler
    discovery         discovery.Backend
    pendingContainers map[string]*pendingContainer

    overcommitRatio float64
    engineOpts      *cluster.EngineOpts
    createRetry     int64
    TLSConfig       *tls.Config
}

其中很重要的是cluster.Engine这个结构体的定义(cluster/engine.go),每个cluster.Engine代表一个Docker engine,即Docker daemon

// Engine represents a docker engine
type Engine struct {
    sync.RWMutex

    ID  string
    IP  string
    Addr string
    Name string
    Cpus int64
    Memory  int64
    Labels  map[string]string
    Version string

    stopCh  chan struct{}
    refreshDelayer  *delayer
    containers  map[string]*Container
    images  []*Image
    networksmap[string]*Network
    volumes map[string]*Volume
    client  dockerclient.Client
    apiClient   engineapi.APIClient
    eventHandlerEventHandler
    state   engineState
    lastError   string
    updatedAt   time.Time
    failureCountint
    overcommitRatio int64
    opts*EngineOpts
    eventsMonitor   *EventsMonitor
}

创建cluster最核心的部分就是addEngine这个方法,即把Docker engine加到cluster中:

func (c *Cluster) addEngine(addr string) bool {
    // Check the engine is already registered by address.
    if c.hasEngineByAddr(addr) {
        return false
    }

    engine := cluster.NewEngine(addr, c.overcommitRatio, c.engineOpts)
    if err := engine.RegisterEventHandler(c); err != nil {
        log.Error(err)
    }
    // Add it to pending engine map, indexed by address. This will prevent
    // duplicates from entering
    c.Lock()
    c.pendingEngines[addr] = engine
    c.Unlock()

    // validatePendingEngine will start a thread to validate the engine.
    // If the engine is reachable and valid, it'll be monitored and updated in a loop.
    // If engine is not reachable, pending engines will be examined once in a while
    go c.validatePendingEngine(engine)

    return true
}

addEngine首先检查当前engine是否已经存在cluster中,如果没有则会分配一个新的engine,同时把它先加到Cluster.pendingEngines中,并启动一个新的goroutinevalidatePendingEngine)去检查它是否是个有效的engine

另外,Engine.RegisterEventHandler实质上就是把ClustereventHandlers成员赋给Engine.eventHandler

// RegisterEventHandler registers an event handler.
func (e *Engine) RegisterEventHandler(h EventHandler) error {
    if e.eventHandler != nil {
        return errors.New("event handler already set")
    }
    e.eventHandler = h
    return nil
}

ClustereventHandlers则是在NewPrimary中赋值的,所以本质上EngineCluster用的都是一套处理函数。

Docker Swarm代码分析笔记(8)——创建Docker API router

上一篇提到的API Server需要设置HTTP处理函数:
......
server.SetHandler(api.NewPrimary(cl, tlsConfig, &statusHandler{cl, nil, nil}, c.GlobalBool("debug"), c.Bool("cors")))
......

api.Server结构体定义如下:

// Server is a Docker API server.
type Server struct {
    hosts  []string
    tlsConfig  *tls.Config
    dispatcher *dispatcher
}

其中处理HTTP请求的相关方法如下:

// Dispatcher is a meta http.Handler. It acts as an http.Handler and forwards
// requests to another http.Handler that can be changed at runtime.
type dispatcher struct {
    handler http.Handler
}

// SetHandler changes the underlying handler.
func (d *dispatcher) SetHandler(handler http.Handler) {
    d.handler = handler
}

// ServeHTTP forwards requests to the underlying handler.
func (d *dispatcher) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    if d.handler == nil {
        httpError(w, "No dispatcher defined", http.StatusInternalServerError)
        return
    }
    d.handler.ServeHTTP(w, r)
}

// SetHandler is used to overwrite the HTTP handler for the API.
// This can be the api router or a reverse proxy.
func (s *Server) SetHandler(handler http.Handler) {
    s.dispatcher.SetHandler(handler)
}

Server.SetHandler所做的就是把handler赋给Server.dispatcher.handlerhandler类型是http.Handler:

type Handler interface {
    ServeHTTP(ResponseWriter, *Request)
}

api.NewPrimary利用了mux这个project

// NewPrimary creates a new API router.
func NewPrimary(cluster cluster.Cluster, tlsConfig *tls.Config, status StatusHandler, debug, enableCors bool) *mux.Router {
    // Register the API events handler in the cluster.
    eventsHandler := newEventsHandler()
    cluster.RegisterEventHandler(eventsHandler)

    context := &context{
        cluster:       cluster,
        eventsHandler: eventsHandler,
        statusHandler: status,
        tlsConfig:     tlsConfig,
    }

    r := mux.NewRouter()
    setupPrimaryRouter(r, context, enableCors)

    if debug {
        profilerSetup(r, "/debug/")
    }

    return r
}

*mux.Router实现了ServeHTTP这个方法,所以符合http.Handler这个interface

// ServeHTTP dispatches the handler registered in the matched route.
//
// When there is a match, the route variables can be retrieved calling
// mux.Vars(request).
func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
    ......
}

api.ServerListenAndServe()函数定义了新的http.Server变量,利用上面实现的api.Server.dispatcherServeHTTP方法来响应HTTP请求:

server = &http.Server{
                Addr:    protoAddrParts[1],
                Handler: s.dispatcher,
            }

再看一下setupPrimaryRouter这个函数:

func setupPrimaryRouter(r *mux.Router, context *context, enableCors bool) {
    for method, mappings := range routes {
        for route, fct := range mappings {
            log.WithFields(log.Fields{"method": method, "route": route}).Debug("Registering HTTP route")

            localRoute := route
            localFct := fct

            wrap := func(w http.ResponseWriter, r *http.Request) {
                log.WithFields(log.Fields{"method": r.Method, "uri": r.RequestURI}).Debug("HTTP request received")
                if enableCors {
                    writeCorsHeaders(w, r)
                }
                context.apiVersion = mux.Vars(r)["version"]
                localFct(context, w, r)
            }
            localMethod := method

            r.Path("/v{version:[0-9]+.[0-9]+}" + localRoute).Methods(localMethod).HandlerFunc(wrap)
            r.Path(localRoute).Methods(localMethod).HandlerFunc(wrap)

            if enableCors {
                optionsMethod := "OPTIONS"
                optionsFct := optionsHandler

                wrap := func(w http.ResponseWriter, r *http.Request) {
                    log.WithFields(log.Fields{"method": optionsMethod, "uri": r.RequestURI}).
                        Debug("HTTP request received")
                    if enableCors {
                        writeCorsHeaders(w, r)
                    }
                    context.apiVersion = mux.Vars(r)["version"]
                    optionsFct(context, w, r)
                }

                r.Path("/v{version:[0-9]+.[0-9]+}" + localRoute).
                    Methods(optionsMethod).HandlerFunc(wrap)
                r.Path(localRoute).Methods(optionsMethod).
                    HandlerFunc(wrap)
            }
        }
    }
}

其中routes定义如下:

var routes = map[string]map[string]handler{
    "HEAD": {
        "/containers/{name:.*}/archive": proxyContainer,
    },
    "GET": {
        "/_ping":                          ping,
        "/events":                         getEvents,
        "/info":                           getInfo,
        ......
        }
    ......
}

"HEAD": {
        "/containers/{name:.*}/archive": proxyContainer,
}

为例:
methodlocalMethod"HEAD"
mappings是:

{
        "/containers/{name:.*}/archive": proxyContainer,
}

routelocalRoute"/containers/{name:.*}/archive"
fctlocalFctproxyContainer
所以

r.Path("/v{version:[0-9]+.[0-9]+}" + localRoute).Methods(localMethod).HandlerFunc(wrap)
r.Path(localRoute).Methods(localMethod).HandlerFunc(wrap)

就是为"/v*/containers/{name:.*}/archive""/containers/{name:.*}/archive"这个PATH"HEAD"操作注册了wrap函数,而wrap函数则封装了localFct,也就是proxyContainer函数。 另外,if enableCors部分与上述类似。

 

Docker Swarm代码分析笔记(7)——创建Docker API server

Docker Swarm manage函数的最后部分是创建Docker API server部分:

server := api.NewServer(hosts, tlsConfig)
if c.Bool("replication") {
    ......
    setupReplication(c, cl, server, discovery, addr, leaderTTL, tlsConfig)
} else {
    server.SetHandler(api.NewPrimary(cl, tlsConfig, &statusHandler{cl, nil, nil}, c.GlobalBool("debug"), c.Bool("cors")))
    cluster.NewWatchdog(cl)
}

log.Fatal(server.ListenAndServe())

Server结构体定义在api/server.go

type Server struct {
    hosts      []string
    tlsConfig  *tls.Config
    dispatcher *dispatcher
}

它的核心方法是ListenAndServe(),即为每个host起一个goroutine监听并处理Docker client的连接请求。

func (s *Server) ListenAndServe() error {
    chErrors := make(chan error, len(s.hosts))

    for _, host := range s.hosts {
        protoAddrParts := strings.SplitN(host, "://", 2)
        if len(protoAddrParts) == 1 {
            protoAddrParts = append([]string{"tcp"}, protoAddrParts...)
        }

        go func() {
            log.WithFields(log.Fields{"proto": protoAddrParts[0], "addr": protoAddrParts[1]}).Info("Listening for HTTP")

            var (
                l      net.Listener
                err    error
                server = &http.Server{
                    Addr:    protoAddrParts[1],
                    Handler: s.dispatcher,
                }
            )

            switch protoAddrParts[0] {
            case "unix":
                l, err = newUnixListener(protoAddrParts[1], s.tlsConfig)
            case "tcp":
                l, err = newListener("tcp", protoAddrParts[1], s.tlsConfig)
            default:
                err = fmt.Errorf("unsupported protocol: %q", protoAddrParts[0])
            }
            if err != nil {
                chErrors <- err
            } else {
                chErrors <- server.Serve(l)
            }

        }()
    }

    for i := 0; i < len(s.hosts); i++ {
        err := <-chErrors
        if err != nil {
            return err
        }
    }
    return nil
}