Fix the following sequence of events:
1. relist call 1 successfully inspects a pod (just has infra container)
1. relist call 2 gets an error inspecting the same pod (has infra container and a transient
container that failed to create) and doesn't update the old/new pod records
1. relist calls 3+ don't inspect the pod any more (just has infra container so it doesn't look like
anything changed)
This change adds a new list that keeps track of pods that failed inspection and retries them the
next time relist is called. Without this change, a pod in this state would never be inspected again,
its entry in the status cache would never be updated, and the pod worker would never call syncPod
again because the most recent entry in the status cache has an error associated with it. Without
this change, pods in this state would be stuck Terminating forever, unless the user issued a
deletion with a grace period value of 0.
PLEG is reponsible for listing the pods running on the node. If it's hung
due to non-responsive container runtime or internal bugs, we should restart
kubelet.
Currently, pleg would report a event if a container transitions from running to
exited between relisting. However, if would not report any event if a container
gets stopped and removed between relisting. This event will eventually be
handled when the pod syncs periodically, but this is undesirable. This change
ensures that we detect all such events.
This change introduces pod lifecycle event generator (PLEG), and adds a generic
PLEG. The generic PLEG relies on relisting to discover container events, and is
container-runtime-agnostic. Both docker and rkt are changed to use generic
PLEG.
Ron Lai