In PodConfigNotificationIncremental PodConfig mode, when no pods are available
for a source, the Merge function correctly concluded that neither ADD, UPDATE nor
REMOVE updates are to be sent to the kubelet. But as a consequence the kubelet will
not mark that source as seen.
This is usually not a problem for the apiserver source. But it is a problem for
an empty "file" source, e.g. by passing an empty directory to the kubelet for
static pods. Then the file source will never be seen and the kubelet will stay
in its special not-all-source-seen mode.
The current implementation considers a source seen when it receives a SET at
kubelet/config/config.go. However, the main kubelet sync loop may not have
received the pod update from the source via the channel. This change ensures
that kubelet would consider all sources are ready only after the sync loop has
seen all the sources.
kubelet relies on source annotation to distinguish pods from different sources.
It should always annotate the source when receiving the pod to avoid any
confusion. This commit fixes that and also make sure we don't overwrite the
first seen time.
A lot of packages use StringSet, but they don't use anything else from
the util package. Moving StringSet into another package will shrink
their dependency trees significantly.
When the pod annotations are updated in the apiserver, update the pod.
Annotations may be used to convey attributes that are required to the
pod execution, such as networking parameters.
Currently, whenever there is any update, kubelet would force all pod workers to
sync again, causing resource contention and hence performance degradation.
This commit flips kubelet to use incremental updates (as opposed to snapshots).
This allows us to know what pods have changed and send updates to those pod
workers only. The `SyncPods` function has been replaced with individual
handlers, each handling an operation (ADD, REMOVE, UPDATE). Pod workers are
still triggered periodically, and kubelet performs periodic cleanup as well.
This commit also spawns a new goroutine solely responsible for killing pods.
This is necessary because pod killing could hold up the sync loop for
indefinitely long amount of time now user can define the graceful termination
period in the container spec.
