StatefulSet AutoDelete blog post #30596

mattcary · 2021-11-22T17:52:13Z

Blog post for statefulset autodelete.

KEP 1847

Implementation PR #99728

netlify · 2021-11-22T18:06:08Z

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netlify · 2021-11-22T18:10:52Z

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sftim

Nice!

One nit though. Please change all the site links to relative links
If you have a hyperlink that starts https://kubernetes.io/docs/, that should be /docs/…

content/en/blog/_posts/2021-12-15-StatefulSet-PVC-Auto-Deletion.md

mattcary · 2021-11-23T16:21:25Z

Nice!

One nit though. Please change all the site links to relative links If you have a hyperlink that starts https://kubernetes.io/docs/, that should be /docs/…

thx, done.

mattcary · 2021-11-23T16:30:38Z

I checked this with a local server and it seems to look good.

sftim · 2021-11-28T19:16:07Z

From a docs (and blog team) point of view, this informally LGTM.

content/en/blog/_posts/2021-12-15-StatefulSet-PVC-Auto-Deletion.md

jimangel · 2021-12-05T23:55:48Z

/milestone v1.23
/cc @jlbutler

k8s-ci-robot · 2021-12-05T23:55:50Z

@jimangel: The provided milestone is not valid for this repository. Milestones in this repository: [1.18-ja.1, 1.18-ja.2, 1.23, dev-1.22-ko.2, dev-1.22-ko.3]

Use /milestone clear to clear the milestone.

In response to this:

/milestone v1.23
/cc @jlbutler

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jimangel · 2021-12-05T23:56:10Z

Take two:
/milestone 1.23

sftim · 2021-12-08T00:40:01Z

@karenhchu is the date (2021-12-16) right for this one?

karenhchu · 2021-12-08T01:00:51Z

@karenhchu is the date (2021-12-16) right for this one?

It's correct. The path also needs to be updated: (content/en/blog/_posts/2021-12-16-StatefulSet-PVC-Auto-Deletion.md)

sftim

@mattcary could you update the path:
content/en/blog/_posts/2021-12-15-StatefulSet-PVC-Auto-Deletion.md
to match the new publication date?

Another option is that we merge this and then do a fixup PR; if you've got the cycles for it, I'd prefer to have it land with the right path.

PS I've mentioned some nits, but those are optional to fix. Only work on those if you do have time.

content/en/blog/_posts/2021-12-15-StatefulSet-PVC-Auto-Deletion.md

sftim · 2021-12-08T01:04:07Z

content/en/blog/_posts/2021-12-15-StatefulSet-PVC-Auto-Deletion.md

+  * **whenDeleted and whenScaled are both Retain.** This matches the existing behavior for StatefulSets, where no PVCs are deleted. This is also the default retention policy. It’s appropriate to use when data on StatefulSet volumes may be irreplaceable and should only be deleted manually.
+
+  * **whenDeleted is Delete and whenScaled is Retain.** In this case, PVCs are deleted only when the entire StatefulSet is deleted. If the StatefulSet is scaled down, PVCs are not touched, meaning they are available to be reattached if a scale-up occurs with any data from the previous replica. This might be used for a temporary StatefulSet, such as in a CI instance or ETL pipeline, where the data on the StatefulSet is needed only during the lifetime of the StatefulSet lifetime, but while the task is running the data is not easily reconstructible. Any retained state is needed for any replicas that scale down and then up.
+
+  * **whenDeleted and whenScaled are both Delete.** PVCs are deleted immediately when their replica is no longer needed. Note this does not include when a Pod is deleted and a new version rescheduled, for example when a node is drained and Pods need to migrate elsewhere. The PVC is deleted only when the replica is no longer needed as signified by a scale-down or StatefulSet deletion. This use case is for when data does not need to live beyond the life of its replica. Perhaps the data is easily reconstructable and the cost savings of deleting unused PVCs is more important than quick scale-up, or perhaps that when a new replica is created, any data from a previous replica is not usable and must be reconstructed anyway.
+
+  * **whenDeleted is Retain and whenScaled is Delete.** This is similar to the previous case, when there is little benefit to keeping PVCs for fast reuse during scale-up. An example of a situation where you might use this is an Elasticsearch cluster.. Typically you would scale that workload up and down to match demand, whilst ensuring a minimum number of replicas (for example: 3). When scaling down, data is migrated away from removed replicas and there is no benefit to retaining those PVCs. However, it can be useful to bring the entire Elasticsearch cluster down temporarily for maintenance. If you need to take the Elasticsearch system offline, you can do this by temporarily deleting the StatefulSet, and then bringing the Elasticsearch cluster back by recreating the StatefulSet. The PVCs holding the Elasticsearch data will still exist and the new replicas will automatically use them.


Within the bold bits, I'd be tempted to put whenDeleted and whenScale in backticks (like I did there). I think it'd actually be easier to read like that.

Also, a nit (I think it might actually be my typo from a previous suggestion):

this is an Elasticsearch cluster.. Typically

two periods

This will also be easier on localization teams if you wrap these at 80 to 100 character length lines, rather than one paragraph per line.

both done.

I also put Retain and Delete in backticks which is consistent what I've done in the text above.

Feedback addressed

sftim · 2021-12-08T01:51:30Z

This could use a technical review from ~~SIG Storage~~ a relevant SIG (I hope: just a formality).
For SIG Docs: /lgtm

mattcary · 2021-12-08T01:53:20Z

/assign @smarterclayton

mattcary · 2021-12-08T01:56:22Z

This could use a technical review from ~~SIG Storage~~ a relevant SIG (I hope: just a formality). For SIG Docs: /lgtm

We had sig-apps review the documentation, @smarterclayton from that sig was kind enough to do that and hopefully his graciousness will continue :)

trathborne · 2021-12-16T13:29:49Z

content/en/blog/_posts/2021-12-16-StatefulSet-PVC-Auto-Deletion.md

+StatefulSet spec template for cases when they should be deleted automatically when the StatefulSet
+is deleted or pods in the StatefulSet are scaled down.
+
+## What problem does this solve?


should there be a blank line after this title?

Markdown (CommonMark) doesn't require a blank line there. See https://deploy-preview-30596--kubernetes-io-main-staging.netlify.app/blog/2021/12/16/kubernetes-1-23-statefulset-pvc-auto-deletion/

trathborne · 2021-12-16T13:31:14Z

content/en/blog/_posts/2021-12-16-StatefulSet-PVC-Auto-Deletion.md

+    retaining those PVCs. However, it can be useful to bring the entire Elasticsearch cluster down
+    temporarily for maintenance. If you need to take the Elasticsearch system offline, you can do
+    this by temporarily deleting the StatefulSet, and then bringing the Elasticsearch cluster back
+    by recreating the StatefulSet. The PVCs holding the Elasticsearch data will still exist and the


"If you need to take the Elasticsearch system offline, you can temporarily delete the StatefulSet, then bring the Elasticsearch cluster back by recreating the StatefulSet." is more concise.

Maybe you're not looking for English editorial, though ☺

I like that better... but given the deadline I think I'll do a post-PR update (see Tim's comment below)

trathborne · 2021-12-16T13:34:38Z

content/en/blog/_posts/2021-12-16-StatefulSet-PVC-Auto-Deletion.md

+    replica. This might be used for a temporary StatefulSet, such as in a CI instance or ETL
+    pipeline, where the data on the StatefulSet is needed only during the lifetime of the
+    StatefulSet lifetime, but while the task is running the data is not easily reconstructible. Any
+    retained state is needed for any replicas that scale down and then up.


If I Retain an openebs-hostpath PVC on scale-down, how does K8s know to scale-up a new Pod on the same Node as the PVC? My understanding of the creation-time scheduling is that the PVC is created on the Node selected for the Pod, but I'm not clear on how the affinity happens for a PVC that exists before the Pod.

I'd have to check that... but since Retain is currently existing behavior, a concise answer is "whatever happens right now" :-)

sftim · 2021-12-16T14:27:24Z

/approve

sftim · 2021-12-16T15:27:14Z

/lgtm

I can't see anything wrong with this article, it's due to publish today, and nobody has raised a serious objection.

k8s-ci-robot · 2021-12-16T15:27:35Z

LGTM label has been added.

Git tree hash: 805c1cfa0f3ab0c94df5cab90efbde51904e3c40

soltysh

/lgtm

soltysh · 2021-12-16T15:24:34Z

content/en/blog/_posts/2021-12-16-StatefulSet-PVC-Auto-Deletion.md

+deleted.
+
+The first situation is when the StatefulSet resource is deleted (which implies that all replicas are
+also deleted). This is controlled by the `whenDeleted` policy. The second situation, controlled by


Suggested change

also deleted). This is controlled by the `whenDeleted` policy. The second situation, controlled by

also deleted). This is controlled by the `whenDeleted` policy field. The second situation, controlled by

soltysh · 2021-12-16T15:26:12Z

content/en/blog/_posts/2021-12-16-StatefulSet-PVC-Auto-Deletion.md

+The first situation is when the StatefulSet resource is deleted (which implies that all replicas are
+also deleted). This is controlled by the `whenDeleted` policy. The second situation, controlled by
+`whenScaled` is when the StatefulSet is scaled down, which removes some but not all of the replicas
+in a StatefulSet. In both cases the policy can either be `Retain`, where the corresponding PVCs are


Suggested change

in a StatefulSet. In both cases the policy can either be `Retain`, where the corresponding PVCs are

in a StatefulSet. In both cases the policy value can either be `Retain`, where the corresponding PVCs are

k8s-ci-robot · 2021-12-16T15:28:53Z

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sftim · 2021-12-16T16:16:08Z

@mattcary if you want to do post-publication tweaks based on #30596 (review) (in a new PR) then please do; if you're happy with it as it is, that's fine also.

mattcary · 2021-12-16T22:59:06Z

@mattcary if you want to do post-publication tweaks based on #30596 (review) (in a new PR) then please do; if you're happy with it as it is, that's fine also.

Thanks Tim. I don't disagree with any of the suggestions, but given bandwidth & review cycles I think I'm happy with the blog post as-is. I appreciate your help with this!

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Doc: Add blogpost for honor PV reclaim policy fix #30556

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StatefulSet AutoDelete blog post #30596

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	also deleted). This is controlled by the `whenDeleted` policy. The second situation, controlled by
	also deleted). This is controlled by the `whenDeleted` policy field. The second situation, controlled by

	in a StatefulSet. In both cases the policy can either be `Retain`, where the corresponding PVCs are
	in a StatefulSet. In both cases the policy value can either be `Retain`, where the corresponding PVCs are

StatefulSet AutoDelete blog post #30596

StatefulSet AutoDelete blog post #30596

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