kubectl subresource KEP #2600

ykakarap · 2021-04-06T15:50:33Z

This KEP proposes adding a --subresource flag to kubectl to be able to fetch and update status and scale subresources.

There is a POC implementation at : kubernetes/kubernetes#99556

For issue: #2590
xref kubernetes/kubectl#564 (comment), kubernetes/kubernetes#15858 (comment), kubernetes/kubernetes#67455
Follow up to kubernetes/kubernetes#60902, kubernetes/kubernetes#67454

nikhita · 2021-04-06T16:12:36Z

/cc @eddiezane @soltysh @seans3 @pwittrock

/assign @eddiezane

nikhita · 2021-04-06T16:12:53Z

/assign @soltysh

keps/sig-cli/2590-kubectl-subresource/README.md

eddiezane · 2021-04-13T16:45:47Z

Demo of this from sig-cli bi-weekly https://youtu.be/zUa7dudYCQM?t=299.

apelisse · 2021-04-13T17:04:59Z

keps/sig-cli/2590-kubectl-subresource/README.md

+```shell
+# For built-in types
+# update spec.replicas through scale subresource
+$ kubectl patch deployment nginx-deployment --subresource='scale' --type='merge' -p '{"spec":{"replicas":2}}'


What's the actual benefit of doing that though?

The ability to modify the scale subresource was added to be consistent with the similar behavior provided to the status subresrouce.

@nikhita if you had any specific uses cases for modifying scale, we should document them in the KEP.

Other than convenience I don't see much value, but I won't object either.

apelisse · 2021-04-13T17:06:22Z

keps/sig-cli/2590-kubectl-subresource/README.md

+
+```shell
+# cron-with-status.yaml has .status.replicas=3
+$ kubectl apply -f cron-with-status.yaml --subresource=status


This will override the last-applied annotation set by another kubectl apply occurence (probably on main resource), which will result in odd behaviors later. Also note that some resources don't allow annotations to be updated through status subresource. That would probably work with server-side apply.

This potentially odd behavior was brought up during the SIG-CLI demo too. I am currently investigating what should be done to handle this properly.

There was another question I brought during the call, if the argument contains just status or full object?

when using apply with subresource it turns out the last-applied annotation is not modified. The annotation is under the metadata section and that section and any changes to the updates are ignored when modifying the subresources.

Therefore any subsequent apply calls to the resource itself are not affected as the patch calculated for the apply call will use the correct last-applied configuration of resource.

The same cannot be said when apply-ing a subresource. The patch calculated using the annotation could be wrong because the last applied configuration of the status is not captured in the annotation.

keps/sig-cli/2590-kubectl-subresource/README.md

soltysh · 2021-04-26T10:58:44Z

keps/sig-cli/2590-kubectl-subresource/README.md

+```shell
+# For built-in types
+# update spec.replicas through scale subresource
+$ kubectl patch deployment nginx-deployment --subresource='scale' --type='merge' -p '{"spec":{"replicas":2}}'


Other than convenience I don't see much value, but I won't object either.

soltysh · 2021-04-26T11:00:00Z

keps/sig-cli/2590-kubectl-subresource/README.md

+
+```shell
+# cron-with-status.yaml has .status.replicas=3
+$ kubectl apply -f cron-with-status.yaml --subresource=status


There was another question I brought during the call, if the argument contains just status or full object?

keps/sig-cli/2590-kubectl-subresource/README.md

ykakarap · 2021-05-06T20:55:36Z

@soltysh I have address all the comments on the comments. Please take a look :)

johnbelamaric · 2021-05-10T19:36:28Z

keps/sig-cli/2590-kubectl-subresource/README.md

+- [ ] Feature gate (also fill in values in `kep.yaml`)
+    - Feature gate name:
+    - Components depending on the feature gate:
+- [x] Other


How does the user know it's alpha?

We don't have an explicit mechanism for stating if a flag is alpha or not, there are a couple of approaches:

Use alpha prefix in the flag name, but I personally don't like that approach since it means we will have to change flag name eventually.

Force using env var, which allows this flag.

Hiding the flag by default, similarly to how deprecated flags are hidden.

Providing a description which is explicitly calling out it's alpha.

I'm personally leaning towards 3 or 4, and given this is an explicit opt-in (you need to place the flag when invoking kubectl command) I'm not worried that users will have issues with that.

+1 for having a description explicitly calling out it's alpha.

Ok, can you pick whatever mechanism is preferred by the SIG and document it here. I don't have a preference really. Otherwise all looks good for PRR, I will approve after that change and the SIG approves.

Updated to option 4 (description explicitly calling out as alpha) and squashed the commits. PTAL :)

soltysh

/lgtm
/approve
from sig-cli pov

soltysh · 2021-05-11T12:04:30Z

keps/sig-cli/2590-kubectl-subresource/README.md

+- [ ] Feature gate (also fill in values in `kep.yaml`)
+    - Feature gate name:
+    - Components depending on the feature gate:
+- [x] Other


We don't have an explicit mechanism for stating if a flag is alpha or not, there are a couple of approaches:

Use alpha prefix in the flag name, but I personally don't like that approach since it means we will have to change flag name eventually.

Force using env var, which allows this flag.

Hiding the flag by default, similarly to how deprecated flags are hidden.

Providing a description which is explicitly calling out it's alpha.

I'm personally leaning towards 3 or 4, and given this is an explicit opt-in (you need to place the flag when invoking kubectl command) I'm not worried that users will have issues with that.

This KEP proposes supporting a new flag `--subresource` to get, patch, edit and replace kubectl commands to fetch and update `status` and `scale` subresources.

soltysh · 2021-05-12T13:52:53Z

/lgtm

johnbelamaric · 2021-05-12T20:36:49Z

/approve

k8s-ci-robot · 2021-05-12T20:37:02Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johnbelamaric, soltysh, ykakarap

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k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Apr 6, 2021

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Add KEP-2590 to support subresources in kubectl

6094074

This KEP proposes supporting a new flag `--subresource` to get, patch, edit and replace kubectl commands to fetch and update `status` and `scale` subresources.

nikhita force-pushed the kubectl_subresource branch from 8b65c13 to 6094074 Compare May 12, 2021 06:18

nikhita mentioned this pull request May 12, 2021

Add subresource support to kubectl #2590

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k8s-ci-robot added the lgtm "Looks good to me", indicates that a PR is ready to be merged. label May 12, 2021

k8s-ci-robot added the approved Indicates a PR has been approved by an approver from all required OWNERS files. label May 12, 2021

k8s-ci-robot merged commit d78aa0c into kubernetes:master May 12, 2021

k8s-ci-robot added this to the v1.22 milestone May 12, 2021

nikhita mentioned this pull request Jan 12, 2023

KEP-2590: graduate kubectl subresource support to beta #3729

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ardaguclu mentioned this pull request Sep 26, 2024

add --subresource to kubectl apply kubernetes/kubernetes#127634

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kubectl subresource KEP #2600

kubectl subresource KEP #2600

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ykakarap commented Apr 6, 2021 •

edited by nikhita

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