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standalone.go
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standalone.go
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package detector
import (
"encoding/binary"
"encoding/json"
"fmt"
"io/ioutil"
"net"
"net/http"
"strconv"
"sync"
"time"
log "github.com/golang/glog"
mesos "github.com/mesos/mesos-go/mesosproto"
"github.com/mesos/mesos-go/upid"
"golang.org/x/net/context"
)
const (
defaultMesosHttpClientTimeout = 10 * time.Second //TODO(jdef) configurable via fiag?
defaultMesosLeaderSyncInterval = 30 * time.Second //TODO(jdef) configurable via fiag?
defaultMesosMasterPort = 5050
)
// enables easier unit testing
type fetcherFunc func(ctx context.Context, address string) (*upid.UPID, error)
type Standalone struct {
ch chan *mesos.MasterInfo
client *http.Client
tr *http.Transport
pollOnce sync.Once
initial *mesos.MasterInfo
done chan struct{}
cancelOnce sync.Once
leaderSyncInterval time.Duration
httpClientTimeout time.Duration
assumedMasterPort int
poller func(pf fetcherFunc)
fetchPid fetcherFunc
}
// Create a new stand alone master detector.
func NewStandalone(mi *mesos.MasterInfo) *Standalone {
log.V(2).Infof("creating new standalone detector for %+v", mi)
stand := &Standalone{
ch: make(chan *mesos.MasterInfo),
tr: &http.Transport{},
initial: mi,
done: make(chan struct{}),
leaderSyncInterval: defaultMesosLeaderSyncInterval,
httpClientTimeout: defaultMesosHttpClientTimeout,
assumedMasterPort: defaultMesosMasterPort,
}
stand.poller = stand._poller
stand.fetchPid = stand._fetchPid
return stand
}
func (s *Standalone) String() string {
return fmt.Sprintf("{initial: %+v}", s.initial)
}
// Detecting the new master.
func (s *Standalone) Detect(o MasterChanged) error {
log.V(2).Info("Detect()")
s.pollOnce.Do(func() {
log.V(1).Info("spinning up asyc master detector poller")
// delayed initialization allows unit tests to modify timeouts before detection starts
s.client = &http.Client{
Transport: s.tr,
Timeout: s.httpClientTimeout,
}
go s.poller(s.fetchPid)
})
if o != nil {
log.V(1).Info("spawning asyc master detector listener")
go func() {
log.V(2).Infof("waiting for polled to send updates")
pollWaiter:
for {
select {
case mi, ok := <-s.ch:
if !ok {
break pollWaiter
}
log.V(1).Infof("detected master change: %+v", mi)
o.OnMasterChanged(mi)
case <-s.done:
return
}
}
o.OnMasterChanged(nil)
}()
} else {
log.Warningf("detect called with a nil master change listener")
}
return nil
}
func (s *Standalone) Done() <-chan struct{} {
return s.done
}
func (s *Standalone) Cancel() {
s.cancelOnce.Do(func() { close(s.done) })
}
// poll for changes to master leadership via current leader's /state.json endpoint.
// we poll the `initial` leader, aborting if none was specified.
//
// TODO(jdef) follow the leader: change who we poll based on the prior leader
// TODO(jdef) somehow determine all masters in cluster from the state.json?
//
func (s *Standalone) _poller(pf fetcherFunc) {
defer func() {
defer s.Cancel()
log.Warning("shutting down standalone master detection")
}()
if s.initial == nil {
log.Errorf("aborting master poller since initial master info is nil")
return
}
addr := s.initial.GetHostname()
if len(addr) == 0 {
if s.initial.GetIp() == 0 {
log.Warningf("aborted mater poller since initial master info has no host")
return
}
ip := make([]byte, 4)
binary.BigEndian.PutUint32(ip, s.initial.GetIp())
addr = net.IP(ip).To4().String()
}
port := uint32(s.assumedMasterPort)
if s.initial.Port != nil && *s.initial.Port != 0 {
port = *s.initial.Port
}
addr = net.JoinHostPort(addr, strconv.Itoa(int(port)))
log.V(1).Infof("polling for master leadership at '%v'", addr)
var lastpid *upid.UPID
for {
startedAt := time.Now()
ctx, cancel := context.WithTimeout(context.Background(), s.leaderSyncInterval)
if pid, err := pf(ctx, addr); err == nil {
if !pid.Equal(lastpid) {
log.V(2).Infof("detected leadership change from '%v' to '%v'", lastpid, pid)
lastpid = pid
elapsed := time.Now().Sub(startedAt)
mi := CreateMasterInfo(pid)
select {
case s.ch <- mi: // noop
case <-time.After(s.leaderSyncInterval - elapsed):
// no one heard the master change, oh well - poll again
goto continuePolling
case <-s.done:
cancel()
return
}
} else {
log.V(2).Infof("no change to master leadership: '%v'", lastpid)
}
} else if err == context.DeadlineExceeded {
if lastpid != nil {
lastpid = nil
select {
case s.ch <- nil: // lost master
case <-s.done: // no need to cancel ctx
return
}
}
goto continuePolling
} else {
select {
case <-s.done:
cancel()
return
default:
if err != context.Canceled {
log.Error(err)
}
}
}
if remaining := s.leaderSyncInterval - time.Now().Sub(startedAt); remaining > 0 {
log.V(3).Infof("master leader poller sleeping for %v", remaining)
time.Sleep(remaining)
}
continuePolling:
cancel()
}
}
// assumes that address is in host:port format
func (s *Standalone) _fetchPid(ctx context.Context, address string) (*upid.UPID, error) {
//TODO(jdef) need SSL support
uri := fmt.Sprintf("http://%s/state.json", address)
req, err := http.NewRequest("GET", uri, nil)
if err != nil {
return nil, err
}
var pid *upid.UPID
err = s.httpDo(ctx, req, func(res *http.Response, err error) error {
if err != nil {
return err
}
defer res.Body.Close()
if res.StatusCode != 200 {
return fmt.Errorf("HTTP request failed with code %d: %v", res.StatusCode, res.Status)
}
blob, err1 := ioutil.ReadAll(res.Body)
if err1 != nil {
return err1
}
log.V(3).Infof("Got mesos state, content length %v", len(blob))
type State struct {
Leader string `json:"leader"` // ex: master(1)@10.22.211.18:5050
}
state := &State{}
err = json.Unmarshal(blob, state)
if err != nil {
return err
}
pid, err = upid.Parse(state.Leader)
return err
})
return pid, err
}
type responseHandler func(*http.Response, error) error
// hacked from https://blog.golang.org/context
func (s *Standalone) httpDo(ctx context.Context, req *http.Request, f responseHandler) error {
// Run the HTTP request in a goroutine and pass the response to f.
ch := make(chan error, 1)
go func() { ch <- f(s.client.Do(req)) }()
select {
case <-ctx.Done():
s.tr.CancelRequest(req)
<-ch // Wait for f to return.
return ctx.Err()
case err := <-ch:
return err
}
}