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Don't cache images when --vmdriver=none #4059

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marcosdiez
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Since #3917, images are cached by default.

That is great, except that it does not make sense when --vmdriver=none.
When cache is enabled,

  • minikube download the images to ~/.minikube/cache
  • minikube loads them (docker load -i ~/.minikube/cache/someimage)

When --vmdriver=none, the machine's docker is used, so any loaded image will be stored there "forever" anyway. Hence they are already cached. And setting the cache enable has actually two downsides:

  • it uses local disk space unnecessarily
  • on every minikube launch it will load images from ~/.minikube/cache/someimage to docker, even though they are there already.

So these 5 lines of code do speedup the launch!

@k8s-ci-robot k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Apr 5, 2019
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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: marcosdiez
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@k8s-ci-robot k8s-ci-robot added the needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. label Apr 5, 2019
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Hi @marcosdiez. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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@k8s-ci-robot k8s-ci-robot added the size/XS Denotes a PR that changes 0-9 lines, ignoring generated files. label Apr 5, 2019
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Can one of the admins verify this patch?

@k8s-ci-robot k8s-ci-robot added size/S Denotes a PR that changes 10-29 lines, ignoring generated files. and removed size/XS Denotes a PR that changes 0-9 lines, ignoring generated files. labels Apr 5, 2019
`docker load -i ~/.minikube/cache/some_images` is unecessary and takes time.
As a bonus, we save disk space.
*/
console.OutStyle("starting-none", "Caching of container images is disabled when --vm-driver=none")
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Remove this line - minikube, particularly with the none driver, has enough console output as is.

@tstromberg
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Thanks for the PR! It looks like it does the right thing - just one minor comment.

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@minikube-bot OK to test

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@afbjorklund afbjorklund left a comment

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Sounds to good me, it is a little disappointing that it reloads images that are already there.

I suppose that is wanted behaviour when using weird "tags" like latest, but maybe it could be fixed for all scenarios - i.e. if we already have the tag (or digest?) maybe we shouldn't be loading anything anywhere

@marcosdiez
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@afbjorklund I believe even with weird tags like latest this is not necessary.

Kubernetes itself has a every interesting policy for tags.
By default, it only tries to check if there is an update if the tag is latest. Else, it will use what's in there or download it in case it does not have it locally. (source: https://kubernetes.io/docs/concepts/containers/images/ )

That means if we cache an image with the latest tag, kubernetes will try to download it again anyway.

Thinking about it a little bit further, it's worse!
Let's say minikube has a cached and "old" version of latest. It would to load it to docker all the time.

Then kubernetes would launch, check the version and download the newest version (because minikube's version is old)

Next time I reboot my laptop and run minikube again, minikube would put back the old version of latest and kubernetes would have to download once more.

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Yeah, that makes sense... And I guess even if you did reload the same image it would still reuse the layers - haven't tested

@@ -174,6 +174,22 @@ func runStart(cmd *cobra.Command, args []string) {
exit.WithError("Failed to generate config", err)
}

if viper.GetString(vmDriver) == constants.DriverNone {
/*
Caching images means:
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I think we can do with a much smaller comment:

// Optimization: images will be persistently loaded into host Docker, so no need to duplicate work.

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And to be policitally correct it should be "the container runtime", not Docker®

@k8s-ci-robot k8s-ci-robot added size/XS Denotes a PR that changes 0-9 lines, ignoring generated files. and removed size/S Denotes a PR that changes 10-29 lines, ignoring generated files. labels Apr 10, 2019
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Thank you!

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5 participants