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kubectl: Fix golint warnings for plugins/*

**What this PR does / why we need it**:

We currently have an entry in `hack/.golint_failures` for `pkg/kubectl/plugins`. If we lint the files in `plugins/` then we can safely remove this entry.
 
`golint` emits the following warnings (only one of each type shown)
```
exported method EnvList.Slice should have comment or be unexported
error var IncompletePluginError should have name of the form ErrFoo
func name will be used as plugins.PluginsEnvVarPluginLoader by other packages, and that stutters; consider calling this EnvVarPluginLoader
```

This PR clears all `golint` warnings from `kubectl/plugins/`.

1. Remove entry from `hack/.golint_failures`
2. Add missing documentation to exported types and functions.
3. Rename error variables to `ErrFoo`.
4. Rename `PluginsEnvVarPluginLoader` to `KubectlPluginsPathPluginLoader` (mirrors env var name).
5. Rename `XDGDataPluginLoader` to `XDGDataDirsPluginLoader` (to make uniform change above).

**Special notes for your reviewer**:

Felt a bit dirty doing this cleanup because the code in `plugins/` is particularly clean and well written already.

**Release note**:

```release-note
NONE
```
/sig cli
/kind cleanup

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ensure unstructured resources in kubectl get

Related downstream issue: https://github.com/openshift/origin/issues/16064

Ensure we are dealing with unstructured objects before attempting to
compose into an unstructured list.

`$ kubectl get ...` [assumes all resources returned from a resource builder are unstructured objects](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubectl/cmd/get.go#L355). This leads to a panic when dealing with non-unstructured objects.
This patch ensures we are dealing with unstructured objects before attempting to
compose into an unstructured list.

**Release note**:
```release-note
NONE
```

cc @fabianofranz @kubernetes/sig-cli-misc

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Avoid hard-coding location for auto-generated cert files

**What this PR does / why we need it**:
This fixes the confusing/incorrect help message for "--tls-cert-file" in apiserver package.

**Which issue this PR fixes**:  fixes #51887 

**Special notes for your reviewer**:
Please advise if a release note is needed.

**Release note**:
```release-note
NONE
```

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Address panic in TestCancelAndReadd

This further increases the timeouts in `timed_workers_test` to reduce the chance of a race condition against the wait group.
Signed-off-by: Monis Khan <mkhan@redhat.com>

Fixes #51704

/assign @gmarek

cc @davidopp @timothysc

```release-note
NONE
```

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Add a kubelet metric to track certificate expiration.

Fix https://github.com/kubernetes/kubernetes/issues/51964

```release-note
Add a metric to the kubelet to monitor remaining lifetime of the certificate that
authenticates the kubelet to the API server.
```

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should use time.Since instead of time.Now().Sub

**What this PR does / why we need it**:

should use time.Since instead of time.Now().Sub

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
NONE
**Special notes for your reviewer**:
NONE
**Release note**:

```release-note
```
NONE

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change AddEventHandlerWithResyncPeriod to AddEventHandler in factory.go
Signed-off-by: zhangjie <zhangjie0619@yeah.net>



**What this PR does / why we need it**:

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
change AddEventHandlerWithResyncPeriod to AddEventHandler in factory.go
```

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double const in mount_linux.go

**What this PR does / why we need it**:
fix some typo and double const
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

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Refactor: Moving disk-related cloud provider operations to gce_disks.go

**What this PR does / why we need it**: The main GCE cloud provider code (pkg/cloudprovider/providers/gce/gce.go) should not contain disk-related operations. Moved them to gce_disks.go

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #51280 

**Release note**:

```release-note
NONE
```
/release-note-none
/sig storage
/assign @msau42 @bowei

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Clean up diskLooksUnformatted literal

**What this PR does / why we need it**:
#16948 moved the `formatAndMount` function to mount_linux.go, but `diskLooksUnformatted` does not necessarily need to appear in mount_unsupported.go
#31515 Renames `diskLooksUnformatted` to `getDiskFormat`, but did not update the comment

This is to do the small cleanup.

**Which issue this PR fixes**

**Special notes for your reviewer**:

**Release note**:

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Omit timeAdded from taint when empty

Fixes omitempty portion of https://github.com/kubernetes/kubernetes/issues/42394

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Add UT for pkg/kubectl/deployment.go

**What this PR does / why we need it**:
I find there is no UT for pkg/kubectl/deployment.go. This PR Adds some UTs for it.

related issue: #50829 

/sig cli

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Allow to specify tls config for etcd in federation coredns provider

Closes: https://github.com/kubernetes/kubernetes/issues/42995

```release-note
CoreDNS provider config allows setting TLS certificates for etcd client.
```

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Add Local and Unstructured resource builder attributes and handle <rsrsc> / <name> pairs when --local is set

**Release note**:
```release-note
NONE
```

Related downstream BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1390139

Adds an error message if a non-filename (or stdin) resource is specified with the `--local` flag in any of the `kube set ...` sub-commands.

cc @fabianofranz @kubernetes/sig-cli-misc

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flexvolume: remove a mount directory in a error case

**What this PR does / why we need it**:

flexVolumeMounter.SetUpAt creates a directory, where a volume has to be
mounted, and we have to remove this directory in a error case. Otherwise
we see errors like this:

Orphaned pod 673b66d9-70f7-11e7-a5fa-525400307392 found, but volume paths are still present on disk

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

https://github.com/kubernetes/kubernetes/issues/49383

**Special notes for your reviewer**:

**Release note**:

Fix a rollback code for the flexvolume mount operation

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kubelet: fix inconsistent display of terminated pod IPs

PLEG and kubelet race when reading and sending pod status to the apiserver.  PLEG
inserts status into a cache, and then signals kubelet.  Kubelet then eventually
reads the status out of that cache, but in the mean time the status could have
been changed by PLEG.

When a pod exits, pod status will no longer include the pod's IP address because
the network plugin/runtime will report "" for terminated pod IPs.  If this status
gets inserted into the PLEG cache before kubelet gets the status out of the cache,
kubelet will see a blank pod IP address.  This happens in about 1/5 of cases when
pods are short-lived, and somewhat less frequently for longer running pods.

To ensure consistency for properties of dead pods, copy an old status update's
IP address over to the new status update if (a) the new status update's IP is
missing and (b) all sandboxes of the pod are dead/not-ready (eg, no possibility
for a valid IP from the sandbox).

Fixes: https://github.com/kubernetes/kubernetes/issues/47265
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1449373

@eparis @freehan @kubernetes/rh-networking @kubernetes/sig-network-misc

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fix some error link of changelog.md and changelog-1.6.md

**What this PR does / why we need it**:
some proposal link in changelog,so change it!
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

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remove duplicated import

**What this PR does / why we need it**:

**Which issue this PR fixes** : fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

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Validate that cronjob names are 52 characters or less

**What this PR does / why we need it**:

Right now when you create a cronjob with a name longer than 52 characters, creation will succeed but the cronjob controller will create Job objects with names longer than 63 characters. Jobs cannot have names longer than 63 characters, so the cronjob will never be able to run any jobs.

**Which issue this PR fixes** : Fixes #50850 

**Special notes for your reviewer**:

**Release note**:
```release-note
Validate that cronjob names are 52 characters or less
```

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Fix url for Saltstack administration document

Got an 404 not found error on `https://kubernetes.io/docs/admin/salt.md`



**What this PR does / why we need it**:

Fixed a wrong url in document

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

NONE

**Release note**:

```release-note
NONE
```

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Release note should not be NONE or similar things.

**What this PR does / why we need it**:
Some release notes are `None` or other similar things. They're meaningless in CHANGELOG.

ref: https://github.com/kubernetes/test-infra/issues/4341 https://github.com/kubernetes/test-infra/issues/4295 https://github.com/kubernetes/test-infra/issues/3295

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:
Hope bot can check such case in the future.

cc @cjwagner 

**Release note**:

```release-note
NONE
```

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add readme file of ipvs

**What this PR does / why we need it**:

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:
```
None
```

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Add CII Best Practices Badge

Thanks to @sarahnovotny in making this happen.

https://bestpractices.coreinfrastructure.org/projects/569Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

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Add cmluciano to NetworkPolicy reviewers

**Release note**:
```
NONE
```

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update comment code mistake

**What this PR does / why we need it**:
update comment code mistake

Fix volume metric flake

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Bump cluster autoscaler to 0.7.0-beta2

This version contains minor bugfixes and updated godeps.

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kubeadm: Use the release-1.8 branch by default

**What this PR does / why we need it**:

In line with https://github.com/kubernetes/kubeadm/blob/master/docs/release-cycle.md, the default branch for kubeadm to deploy should be bumped right before the `rc.1`.
This can even be manually merged by the someone from the release team.

Adding do-not-merge until we're ready for the release candidate.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
fixes: https://github.com/kubernetes/kubeadm/issues/427

**Special notes for your reviewer**:

**Release note**:

```release-note
kubeadm: Use the release-1.8 branch by default
```
@kubernetes/sig-cluster-lifecycle-pr-reviews @kubernetes/kubernetes-release-managers

Make sure we only run this test in environments
that support it.

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Add e2e test to verify PVC metrics

Adds an e2e test for kubernetes/features#363

fixes #52459

Fake out the kubernetes version in phase testing in order to avoid resolving things manually (which can lead to flakes)

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In autoscaling tests, improve setting pdbs for kube-system pods

This fixes selector for l7-default-backend pod and removes Heapster's PDB (it's harmless but pointless as CA won't be able to evict it due to other constraints).

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GlusterFS plugin fails to mount volumes in 1.7.3 branch #50463