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lb_agent.go
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lb_agent.go
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package agent
import (
"bytes"
"context"
"errors"
"io"
"io/ioutil"
"net/http"
"time"
"github.com/sirupsen/logrus"
"go.opencensus.io/trace"
"github.com/fnproject/fn/api/common"
"github.com/fnproject/fn/api/models"
pool "github.com/fnproject/fn/api/runnerpool"
"github.com/fnproject/fn/fnext"
)
type lbAgent struct {
cfg Config
callListeners []fnext.CallListener
rp pool.RunnerPool
placer pool.Placer
callOverrider CallOverrider
shutWg *common.WaitGroup
callOpts []CallOpt
}
type DetachedResponseWriter struct {
Headers http.Header
status int
acked chan struct{}
}
func (w *DetachedResponseWriter) Header() http.Header {
return w.Headers
}
func (w *DetachedResponseWriter) Write(data []byte) (int, error) {
return len(data), nil
}
func (w *DetachedResponseWriter) WriteHeader(statusCode int) {
w.status = statusCode
w.acked <- struct{}{}
}
func (w *DetachedResponseWriter) Status() int {
return w.status
}
func NewDetachedResponseWriter(h http.Header, statusCode int) *DetachedResponseWriter {
return &DetachedResponseWriter{
Headers: h,
status: statusCode,
acked: make(chan struct{}, 1),
}
}
var _ http.ResponseWriter = new(DetachedResponseWriter) // keep the compiler happy
type LBAgentOption func(*lbAgent) error
// WithLBAgentConfig sets the agent config to the provided Config
func WithLBAgentConfig(cfg *Config) LBAgentOption {
return func(a *lbAgent) error {
a.cfg = *cfg
return nil
}
}
// WithLBCallOverrider is for LB agents to register a CallOverrider to modify a Call and extensions
func WithLBCallOverrider(fn CallOverrider) LBAgentOption {
return func(a *lbAgent) error {
if a.callOverrider != nil {
return errors.New("lb-agent call overriders already exists")
}
a.callOverrider = fn
return nil
}
}
// WithLBCallOptions adds additional call options to each call created from GetCall, these
// options will be executed after any other options supplied to GetCall
func WithLBCallOptions(opts ...CallOpt) LBAgentOption {
return func(a *lbAgent) error {
a.callOpts = append(a.callOpts, opts...)
return nil
}
}
// NewLBAgent creates an Agent that knows how to load-balance function calls
// across a group of runner nodes.
func NewLBAgent(rp pool.RunnerPool, p pool.Placer, options ...LBAgentOption) (Agent, error) {
// Yes, LBAgent and Agent both use a Config.
cfg, err := NewConfig()
if err != nil {
logrus.WithError(err).Fatalf("error in lb-agent config cfg=%+v", cfg)
}
a := &lbAgent{
cfg: *cfg,
rp: rp,
placer: p,
shutWg: common.NewWaitGroup(),
}
// Allow overriding config
for _, option := range options {
err = option(a)
if err != nil {
logrus.WithError(err).Fatalf("error in lb-agent options")
}
}
logrus.Infof("lb-agent starting cfg=%+v", a.cfg)
return a, nil
}
// implements Agent
func (a *lbAgent) AddCallListener(listener fnext.CallListener) {
a.callListeners = append(a.callListeners, listener)
}
// implements callTrigger
func (a *lbAgent) fireBeforeCall(ctx context.Context, call *models.Call) error {
return fireBeforeCallFun(a.callListeners, ctx, call)
}
// implements callTrigger
func (a *lbAgent) fireAfterCall(ctx context.Context, call *models.Call) error {
return fireAfterCallFun(a.callListeners, ctx, call)
}
// implements Agent
func (a *lbAgent) GetCall(opts ...CallOpt) (Call, error) {
var c call
// add additional agent options after any call specific options
opts = append(opts, a.callOpts...)
for _, o := range opts {
err := o(&c)
if err != nil {
return nil, err
}
}
// TODO typed errors to test
if c.req == nil || c.Call == nil {
return nil, errors.New("no model or request provided for call")
}
// If overrider is present, let's allow it to modify models.Call
// and call extensions
if a.callOverrider != nil {
ext, err := a.callOverrider(c.req, c.Call, c.extensions)
if err != nil {
return nil, err
}
c.extensions = ext
}
setupCtx(&c)
c.ct = a
c.stderr = common.NoopReadWriteCloser{}
return &c, nil
}
// implements Agent
func (a *lbAgent) Close() error {
// start closing the front gate first
ch := a.shutWg.CloseGroupNB()
// finally shutdown the runner pool
err := a.rp.Shutdown(context.Background())
if err != nil {
logrus.WithError(err).Warn("Runner pool shutdown error")
}
// gate-on front-gate, should be completed if delegated agent & runner pool is gone.
<-ch
return err
}
// implements Agent
func (a *lbAgent) Submit(callI Call) error {
call := callI.(*call)
ctx, span := trace.StartSpan(call.req.Context(), "lb_agent_submit")
defer span.End()
span.AddAttributes(
trace.StringAttribute("fn.call_id", call.ID),
trace.StringAttribute("fn.app_id", call.AppID),
trace.StringAttribute("fn.fn_id", call.FnID),
)
rid := common.RequestIDFromContext(ctx)
if rid != "" {
span.AddAttributes(
trace.StringAttribute("fn.rid", rid),
)
}
statsCalls(ctx)
if !a.shutWg.AddSession(1) {
statsTooBusy(ctx)
return models.ErrCallTimeoutServerBusy
}
defer a.shutWg.DoneSession()
statsEnqueue(ctx)
// pre-read and buffer request body if already not done based
// on GetBody presence.
buf, err := a.setRequestBody(ctx, call)
if buf != nil {
defer bufPool.Put(buf)
}
if err != nil {
return a.handleCallEnd(ctx, call, err, false)
}
err = call.Start(ctx)
if err != nil {
return a.handleCallEnd(ctx, call, err, false)
}
statsDequeue(ctx)
statsStartRun(ctx)
if call.Type == models.TypeDetached {
return a.placeDetachCall(ctx, call)
}
return a.placeCall(ctx, call)
}
func (a *lbAgent) placeDetachCall(ctx context.Context, call *call) error {
errPlace := make(chan error, 1)
rw := call.respWriter.(*DetachedResponseWriter)
go a.spawnPlaceCall(ctx, call, errPlace)
select {
case err := <-errPlace:
return err
case <-rw.acked:
return nil
}
}
func (a *lbAgent) placeCall(ctx context.Context, call *call) error {
err := a.placer.PlaceCall(ctx, a.rp, call)
return a.handleCallEnd(ctx, call, err, true)
}
func (a *lbAgent) spawnPlaceCall(ctx context.Context, call *call, errCh chan error) {
var cancel func()
ctx = common.BackgroundContext(ctx)
cfg := a.placer.GetPlacerConfig()
// PlacerTimeout for Detached + call.Timeout (inside container) + headroom for docker-pull, gRPC network retrasmit etc.)
newCtxTimeout := cfg.DetachedPlacerTimeout + time.Duration(call.Timeout)*time.Second + a.cfg.DetachedHeadRoom
ctx, cancel = context.WithTimeout(ctx, newCtxTimeout)
defer cancel()
err := a.placer.PlaceCall(ctx, a.rp, call)
errCh <- a.handleCallEnd(ctx, call, err, true)
}
// setRequestGetBody sets GetBody function on the given http.Request if it is missing. GetBody allows
// reading from the request body without mutating the state of the request.
func (a *lbAgent) setRequestBody(ctx context.Context, call *call) (*bytes.Buffer, error) {
r := call.req
if r.Body == nil || r.GetBody != nil {
return nil, nil
}
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
// WARNING: we need to handle IO in a separate go-routine below
// to be able to detect a ctx timeout. When we timeout, we
// let gin/http-server to unblock the go-routine below.
errApp := make(chan error, 1)
go func() {
_, err := buf.ReadFrom(r.Body)
if err != nil && err != io.EOF {
errApp <- err
return
}
r.Body = ioutil.NopCloser(bytes.NewReader(buf.Bytes()))
// GetBody does not mutate the state of the request body
r.GetBody = func() (io.ReadCloser, error) {
return ioutil.NopCloser(bytes.NewReader(buf.Bytes())), nil
}
close(errApp)
}()
select {
case err := <-errApp:
return buf, err
case <-ctx.Done():
return buf, ctx.Err()
}
}
// implements Agent
func (a *lbAgent) Enqueue(context.Context, *models.Call) error {
logrus.Error("Enqueue not implemented")
return errors.New("Enqueue not implemented")
}
func (a *lbAgent) handleCallEnd(ctx context.Context, call *call, err error, isForwarded bool) error {
if isForwarded {
call.End(ctx, err)
statsStopRun(ctx)
if err == nil {
statsComplete(ctx)
recordCallLatency(ctx, call, completedMetricName)
} else if err == context.DeadlineExceeded {
// We are here because we were unable to service this request for the given
// reservation. In detached case, the reservation is calculated based on estimated
// total time to run a request. (See: spawnPlaceCall) Otherwise, there's no set
// deadline in the request context. This is also a bit more robust going forward
// if we start enforcing a maximum overall deadline for clients. For detached case, the
// error is unlikely to be delivered to the client since this is essentially an async
// operation.
statsTimedout(ctx)
recordCallLatency(ctx, call, timedoutMetricName)
// We have failed: http 500 Internal Server Error
return models.ErrServiceReservationFailure
}
} else {
statsDequeue(ctx)
if err == context.DeadlineExceeded {
statsTooBusy(ctx)
recordCallLatency(ctx, call, serverBusyMetricName)
return models.ErrCallTimeoutServerBusy
}
}
if err == models.ErrCallTimeoutServerBusy {
statsTooBusy(ctx)
recordCallLatency(ctx, call, serverBusyMetricName)
return models.ErrCallTimeoutServerBusy
} else if err == context.Canceled {
statsCanceled(ctx)
recordCallLatency(ctx, call, canceledMetricName)
} else if err != nil {
statsErrors(ctx)
recordCallLatency(ctx, call, errorsMetricName)
}
return err
}
func recordCallLatency(ctx context.Context, call *call, status string) {
start := time.Time(call.StartedAt)
creat := time.Time(call.CreatedAt)
// IMPORTANT: Why do we prefer 'StartedAt'? This is because we would like to
// exclude client transmission of the request body to the LB. We are trying to
// measure how long it took us to execute a user function and obtain its response.
// Notice how we cache client body *before* we call call.Start() where StartedAt
// is set. If call.Start() is not called yet, then we use call.CreatedAt.
var callLatency time.Duration
if !start.IsZero() {
callLatency = time.Now().Sub(start)
} else if !creat.IsZero() {
callLatency = time.Now().Sub(creat)
} else {
common.Logger(ctx).Error("cannot determine call start time")
return
}
// We want to exclude time spent in user-code. Today, this is container
// request processing latency as observed by runner agent.
execLatency := call.GetUserExecutionTime()
// some sanity check before. If sanity checks flags something, then
// this is likely that runners are sending malicious/suspicious data.
if execLatency != nil {
if *execLatency >= callLatency {
common.Logger(ctx).Errorf("invalid latency callLatency=%v execLatency=%v", callLatency, execLatency)
return
}
callLatency -= *execLatency
}
statsCallLatency(ctx, callLatency, status)
}
var _ Agent = &lbAgent{}
var _ callTrigger = &lbAgent{}