Recap of related tangent in #2483 follows.

Use case: I need to implement mesos task reconciliation in the kubernetes-mesos scheduler. If it crashes and then restarts, I want to be able to recover things like taskID, slaveID, offerID, etc. so as to rebuild the internal state of the scheduler. Once state is recovered, I can reconcile the against the tasks that the mesos master knows about.

If I can't use binding annotations for this, then I need to store state some other (super inconvenient) way. Currently the etcd registry assignPod() implementation drops binding annotations on the floor. It should not, and instead they should be preserved for later access.

Proposal: Store binding-related annotations in a new field: Pod.Status.Annotations

• When setting Pod.Status.Host="{some-host-name}" via assignPod(), binding annotations are copied in from Binding
• When cloning Pod.Status.Host in UpdatePod() (for an already-scheduled pod), the Pod.Status.Annotations are also cloned.

I don't think /bindings has to be a readable apiserver endpoint, as long as the binding metadata is exposed some other way, as proposed above.

I'd also like to propose that once binding annotations are "bound" to Pod.Status they become read-only. So they're essentially write-once, just like Pod.Status.Host is meant to be.

cc @smarterclayton @bgrant0607 @erictune
xref d2iq-archive/kubernetes-mesos#73