As we work towards providing a stable (v1) kubeletconfig API,
we cannot afford to have deprecated or "experimental" (alpha) fields
living in the KubeletConfiguration struct. This removes all existing
experimental or deprecated fields, and places them in KubeletFlags
instead.
I'm going to send another PR after this one that organizes the remaining
fields into substructures for readability. Then, we should try to move
to v1 ASAP.
It makes far more sense to focus on a clean API in kubeletconfig v2,
than to try and further clean up the existing "API" that everyone
already depends on.
Automatic merge from submit-queue
Remove null -> [] slice hack
Closes#44593
When 1.6 added protobuf storage, the storage layer lost the ability to persist slice fields with empty but non-null values.
As a workaround, we tried to convert empty slice fields to `[]`, rather than `null`. Compressing `null` -> `[]` was just as much of an API breakage as `[]` -> `null`, but was hoped to cause fewer problems in clients that don't do null checks.
Because of conversion optimizations around converting lists of objects, the `null` -> `[]` hack was discovered to only apply to individual get requests, not to a list of objects. 1.6 and 1.7 was released with this behavior, and the world didn't explode. 1.7 documented the breaking API change that `null` and `[]` should be considered equivalent, unless otherwise noted on a particular field.
This PR:
* Reverts the earlier attempt (https://github.com/kubernetes/kubernetes/pull/43422) at ensuring non-null json slice output in conversion
* Makes results of `get` consistent with the results of `list` (which helps naive clients that do deepequal comparisons of objects obtained via list/watch and get), and allows empty slice fields to be returned as `null`
```release-note
Protobuf serialization does not distinguish between `[]` and `null`.
API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field) can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6+). JSON API clients should tolerate `null` values for such fields, and treat `null` and `[]` as equivalent in meaning unless specifically documented otherwise for a particular field.
```
The ReadOnlyPort defaulting prevented passing 0 to diable via
the KubeletConfiguraiton struct.
The HealthzPort defaulting prevented passing 0 to disable via the
KubeletConfiguration struct. The documentation also failed to mention
this, but the check is performed in code.
The CAdvisorPort documentation failed to mention that you can pass 0 to
disable.
The subfeature was a cool idea, but in the end it is very complex to
separate Kubelet restarts into crash-loops caused by config vs.
crash-loops caused by other phenomena, like admin-triggered node restarts,
kernel panics, and and process babysitter behavior. Dynamic kubelet config
will be better off without the potential for false positives here.
Removing this subfeature also simplifies dynamic configuration by
reducing persistent state:
- we no longer need to track bad config in a file
- we no longer need to track kubelet startups in a file
