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container/controller: avoid cancellation with forked pull context

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Context cancellations were previously causing `Prepare` to fail
completely on re-entrant calls. To prevent this, we filtered out cancels
and deadline errors. While this allowed the service to proceed without
errors, it had the possibility of interrupting long pulls, causing the
pull to happen twice.

This PR forks the context of the pull to match the lifetime of
`Controller`, ensuring that for each task, the pull is only performed
once. It also ensures that multiple calls to `Prepare` are re-entrant,
ensuring that the pull resumes from its original position.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day 2016-07-25 20:59:02 -07:00
parent a6a261261d
commit d8d71ad5b9
No known key found for this signature in database
GPG key ID: FB5F6B2905D7ECF3
1 changed files with 53 additions and 17 deletions
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46
daemon/cluster/executor/container/controller.go
View file

@ -24,6 +24,10 @@ type controller struct {
adapter *containerAdapter
closed chan struct{}
err error
pulled chan struct{} // closed after pull
cancelPull func() // cancels pull context if not nil
pullErr error // pull error, only read after pulled closed
}
var _ exec.Controller = &controller{}
@ -86,12 +90,27 @@ func (r *controller) Prepare(ctx context.Context) error {
}
if os.Getenv("DOCKER_SERVICE_PREFER_OFFLINE_IMAGE") != "1" {
if err := r.adapter.pullImage(ctx); err != nil {
cause := errors.Cause(err)
if cause == context.Canceled || cause == context.DeadlineExceeded {
return err
if r.pulled == nil {
// Fork the pull to a different context to allow pull to continue
// on re-entrant calls to Prepare. This ensures that Prepare can be
// idempotent and not incur the extra cost of pulling when
// cancelled on updates.
var pctx context.Context
r.pulled = make(chan struct{})
pctx, r.cancelPull = context.WithCancel(context.Background()) // TODO(stevvooe): Bind a context to the entire controller.
go func() {
defer close(r.pulled)
r.pullErr = r.adapter.pullImage(pctx) // protected by closing r.pulled
}()
}
select {
case <-ctx.Done():
return ctx.Err()
case <-r.pulled:
if r.pullErr != nil {
// NOTE(stevvooe): We always try to pull the image to make sure we have
// the most up to date version. This will return an error, but we only
// log it. If the image truly doesn't exist, the create below will
@ -103,7 +122,8 @@ func (r *controller) Prepare(ctx context.Context) error {
//
// If you don't want this behavior, lock down your image to an
// immutable tag or digest.
log.G(ctx).WithError(err).Error("pulling image failed")
log.G(ctx).WithError(r.pullErr).Error("pulling image failed")
}
}
}
@ -252,6 +272,10 @@ func (r *controller) Shutdown(ctx context.Context) error {
return err
}
if r.cancelPull != nil {
r.cancelPull()
}
if err := r.adapter.shutdown(ctx); err != nil {
if isUnknownContainer(err) || isStoppedContainer(err) {
return nil
@ -269,6 +293,10 @@ func (r *controller) Terminate(ctx context.Context) error {
return err
}
if r.cancelPull != nil {
r.cancelPull()
}
if err := r.adapter.terminate(ctx); err != nil {
if isUnknownContainer(err) {
return nil
@ -286,6 +314,10 @@ func (r *controller) Remove(ctx context.Context) error {
return err
}
if r.cancelPull != nil {
r.cancelPull()
}
// It may be necessary to shut down the task before removing it.
if err := r.Shutdown(ctx); err != nil {
if isUnknownContainer(err) {
@ -320,6 +352,10 @@ func (r *controller) Close() error {
case <-r.closed:
return r.err
default:
if r.cancelPull != nil {
r.cancelPull()
}
r.err = exec.ErrControllerClosed
close(r.closed)
}