tests: Adds [LinuxOnly] tag to conformance test

[claudiubelu]

What type of PR is this?

/kind failing-test

/sig testing
/sig windows

What this PR does / why we need it:

The test "should write entries to /etc/hosts" should have the [LinuxOnly] tag as
it cannot pass on Windows; individual files cannot be mounted in Windows Containers.

This test was missed in the original PR (#73204)

Which issue(s) this PR fixes:

Related Issue: #69871

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @BCLAU. Thanks for your PR.

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[dims]

/area conformance
/ok-to-test

@BCLAU please consider applying for membership to the kubernetes github org :)

[dims]

@yujuhong @Random-Liu Does this look good to you?

/sig node

[adelina-t]

/lgtm

[adelina-t]

/cc @PatrickLang

[yujuhong]

/lgtm
/approve

[claudiubelu]

/assign @pwittrock

[neolit123]

/lgtm

[neolit123]

/priority important-soon

[justinsb]

Shouldn't HostAliases work on Windows?

The logic here isn't clear to me also - I see the justification as "individual files cannot be mounted in Windows Containers" yet I don't see any files being mounted. My understanding is that /etc/hosts is typically copied into the containers on linux, not mounted.

[neolit123]

Shouldn't HostAliases work on Windows?

hm, i don't know what was decided for GA.

possibly the comment for the [LinuxOnly] tag needs clarification:
https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/kubelet_pods.go#L131-L137

related issue:
#70189

[justinsb]

Good links, thanks @neolit123!

AFAIK HostAliases isn't critical enough that it should be a blocker for windows support, but I do think we should be excruciatingly precise about why we are excluding it, as it is a conformance test.

[claudiubelu]

Shouldn't HostAliases work on Windows?

The logic here isn't clear to me also - I see the justification as "individual files cannot be mounted in Windows Containers" yet I don't see any files being mounted. My understanding is that /etc/hosts is typically copied into the containers on linux, not mounted.

No, the /etc/hosts file is mounted into containers. Here's an example of a Linux Pod's container, see the /etc/hosts file mount: https://paste.ubuntu.com/p/Hq2z2GFQDF/ . And as this PR says, individual files cannot be mounted on Windows Containers.

Although, copying the hosts file into the container could be a viable alternative. However, that is outside the scope of this PR or the target for this release. This can be further discussed for v1.15.

PS: updated test description to include a more detailed explanation.

[neolit123]

/lgtm
thanks for the comment update.

[PatrickLang]

re: single file mapping

This is something that's possible in Windows Server 2019, but not with the Docker codebase. It has been implemented in containerd, but containerd is not stable enough to take it for 1.14. Rather than implementing a workaround of replacing a file after the pod starts, I think it would be best to do the right fix and support /etc/hosts -> c:\windows\system32\drivers\etc\hosts mapping for 1.15 or 1.16 when ContainerD is ready.

[spiffxp]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bclau, spiffxp, yujuhong

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[PatrickLang]

/retest