fieldManager: Ignore conversion errors to internal types

Errors on updates are bad because they usually come from controllers and
it's very hard to take actions on them. We also don't want to start
breaking kubernetes clusters if something in a schema happens a way we
didn't foresee (even though we've tried to be diligent and test as much
as possible, these can still happen).

Log an identifiable error when they happen. Ideally people can look in
the logs to find these and report them, or providers can look for these
in logs and make sure they don't happen.

Only conversion to internal types are going to be logged and ignored.

It means that we're still failing for:
- Version conversions. If we can't convert the object from one version
  to another,
- Unions. If we can't normalize the union,
- Invalid MangedFields sent in the object. If something has changed the
  ManagedFields to an invalid value.
- Failure to serialize the manager information, this really shouldn't
  happen.
- Encoding the ManagedFields

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/BUILD

@@ -14,6 +14,7 @@ go_library(
         "//staging/src/k8s.io/apimachinery/pkg/runtime:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal:go_default_library",
+        "//vendor/k8s.io/klog:go_default_library",
         "//vendor/k8s.io/kube-openapi/pkg/util/proto:go_default_library",
         "//vendor/sigs.k8s.io/structured-merge-diff/fieldpath:go_default_library",
         "//vendor/sigs.k8s.io/structured-merge-diff/merge:go_default_library",

staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/fieldmanager.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal"
+	"k8s.io/klog"
 	openapiproto "k8s.io/kube-openapi/pkg/util/proto"
 	"sigs.k8s.io/structured-merge-diff/fieldpath"
 	"sigs.k8s.io/structured-merge-diff/merge"
@@ -115,11 +116,15 @@ func (f *FieldManager) Update(liveObj, newObj runtime.Object, manager string) (r
 	internal.RemoveObjectManagedFields(newObjVersioned)
 	newObjTyped, err := f.typeConverter.ObjectToTyped(newObjVersioned)
 	if err != nil {
-		return nil, fmt.Errorf("failed to create typed new object: %v", err)
+		// Return newObj and just by-pass fields update. This really shouldn't happen.
+		klog.Errorf("[SHOULD NOT HAPPEN] failed to create typed new object: %v", err)
+		return newObj, nil
 	}
 	liveObjTyped, err := f.typeConverter.ObjectToTyped(liveObjVersioned)
 	if err != nil {
-		return nil, fmt.Errorf("failed to create typed live object: %v", err)
+		// Return newObj and just by-pass fields update. This really shouldn't happen.
+		klog.Errorf("[SHOULD NOT HAPPEN] failed to create typed live object: %v", err)
+		return newObj, nil
 	}
 	apiVersion := fieldpath.APIVersion(f.groupVersion.String())
 	manager, err = f.buildManagerInfo(manager, metav1.ManagedFieldsOperationUpdate)