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Sidecar Containers #753

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Joseph-Irving opened this issue Jan 29, 2019 · 159 comments
Closed

Sidecar Containers #753

Joseph-Irving opened this issue Jan 29, 2019 · 159 comments
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kind/api-change Categorizes issue or PR as related to adding, removing, or otherwise changing an API kind/feature Categorizes issue or PR as related to a new feature. sig/apps Categorizes an issue or PR as relevant to SIG Apps. sig/node Categorizes an issue or PR as relevant to SIG Node. stage/alpha Denotes an issue tracking an enhancement targeted for Alpha status tracked/no Denotes an enhancement issue is NOT actively being tracked by the Release Team

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@Joseph-Irving
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Joseph-Irving commented Jan 29, 2019

Enhancement Description

/kind feature
/sig apps
/sig node

@k8s-ci-robot k8s-ci-robot added kind/feature Categorizes issue or PR as related to a new feature. sig/apps Categorizes an issue or PR as relevant to SIG Apps. sig/node Categorizes an issue or PR as relevant to SIG Node. labels Jan 29, 2019
@Joseph-Irving
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Joseph-Irving commented Jan 29, 2019

@enisoc @dchen1107 @fejta @thockin @kow3ns @derekwaynecarr, opened this tracking issue so that we can discuss.

@kow3ns
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kow3ns commented Jan 31, 2019

/assign

@Joseph-Irving
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Joseph-Irving commented Feb 1, 2019

@derekwaynecarr I've done some scoping out of the kubelet changes required for next week's sig-node meeting, I believe that changes are only needed in the kuberuntime package, specifically kuberuntime_manager.go in and kuberuntime_container.go.

In kuberuntime_manager.go you could modify computePodActions to implement the shutdown triggering (kill sidecars when all non-sidecars have permanently exited), and starting up the sidecars first.

In kuberuntime_container.go you could modify killContainersWithSyncResult for terminating the sidecars last and sending the preStop hooks (the preStop hooks bit was a bit debatable, it wasn't settled whether that should be done or not. @thockin had a good point about why you might not want to encourage that behaviour, see comment).

Let me know if you want me to investigate any further.

@resouer
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resouer commented Feb 1, 2019

@kow3ns The discussion makes more sense to me if maybe we can define a full description of containers sequence in Pod spec (sig-app), and how to handle the sequence in kubelet for start, restart and cascading consideration (sig-node). Let's catch the Feb 5 sig-node meeting to give more inputs.

cc @Joseph-Irving

@luksa
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luksa commented Feb 7, 2019

The proposal says that sidecars only run after the init containers run. But what if the use-case requires the sidecar to run while/before the init containers run. For example, if you'd like route the pod's traffic through a proxy running as a sidecar (as in Istio), you probably want that proxy to be in place while the init containers run in case the init container itself does network calls.

@Joseph-Irving
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Joseph-Irving commented Feb 14, 2019

@luksa I think there's the possibility of looking at having sidecars that run in init phase at some point but currently the proposal is not going to cover that use case. There is currently no way to have concurrent containers running in the init phase so that would be potentially a much larger/messier change than what is being suggested here.

@Joseph-Irving
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Joseph-Irving commented Feb 14, 2019

Update on this KEP:
I've spoken to both @derekwaynecarr and @dchen1107 from sig-node about this and they did not express any major concerns about the proposal. I will raise a PR to the KEP adding some initial notes around implementation details and clarifying a few points that came up during the discussion.

We still need to agree on the API, it seems there is consensus that a simple way of marking containers as sidecars is prefered over more in depth ordering flags. Having a bool is somewhat limiting though so perhaps something more along the lines of containerLifecycle: Sidecar would be preferable so that we have the option of expanding in the future.

@luksa
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luksa commented Feb 14, 2019

@Joseph-Irving Actually, neither the boolean nor the containerLifecycle: Sidecar are appropriate for proper future extensibility. Instead, containerLifecycle should be an object, just like deployment.spec.strategy, with type: Sidecar. This would allow us to then introduce additional fields. For the "sidecar for the whole lifetime of the pod" solution, it would be expressed along these lines:

containerLifecycle: 
  type: Sidecar
  sidecar:
    scope: CompletePodLifetime

as opposed to

containerLifecycle: 
  type: Sidecar
  sidecar:
    scope: AfterInit

Please forgive my bad naming - I hope the names convey the idea.

But there is one problem with the approach where we introduce containerLifecycle to pod.spec.containers. Namely, it's wrong to have sidecars that run parallel to init containers specified under pod.spec.containers. So if you really want to be able to extend this to init containers eventually, you should find an alternative solution - one that would allow you to mark containers as sidecars at a higher level - i.e. not under pod.spec.containers or pod.spec.initContainers, but something like pod.spec.sidecarContainers, which I believe you already discussed, but dismissed. The init containers problem definitely calls for a solution along these lines.

@Joseph-Irving
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Joseph-Irving commented Feb 14, 2019

@luksa You could also solve the init problem by just allowing an init container to be marked as a sidecar and have that run alongside the init containers. As I understand it, the problem is that init containers sometimes need sidecars, which is different from needing a container that runs for the entire lifetime of the pod.

The problem with pod.spec.sidecarContainers is that it's a far more complex change, tooling would need to updated and the kubelet would require a lot of modifying to support another set of containers. The current proposal is far more modest, it's only building on what's already there.

@luksa
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luksa commented Feb 14, 2019

@Joseph-Irving We could work with that yes. It's not ideal for the sidecar to shut down after the init containers run and then have the same sidecar start up again, but it's better than not having that option. The bigger problem is that older Kubelets wouldn't handle init-sidecar containers properly (as is the case with main-sidecar containers).

I'd just like you to keep init-sidecars in mind when finalizing the proposal. In essence, you're introducing the concept of "sidecar" into k8s (previously, we basically only had a set of containers that were all equal). Now you're introducing actual sidecars, so IMHO, you really should think this out thoroughly and not dismiss a very important sidecar use-case.

I'd be happy to help with implementing this. Without it, Istio can't provide its features to init containers (actually, in a properly secured Kubernetes cluster running Istio, init containers completely lose the ability to talk to any service).

@Joseph-Irving
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Joseph-Irving commented Mar 7, 2019

In relation to the implementation discussion in #841, I've opened a WIP PR containing a basic PoC for this proposal kubernetes/kubernetes#75099. It's just a first draft and obviously not perfect but the basic functionality works and gives you an idea of the amount of change required.

cc @enisoc

@Joseph-Irving
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Joseph-Irving commented Mar 18, 2019

I put together a short video just showing how the PoC currently behaves https://youtu.be/4hC8t6_8bTs. Seeing it in action can be better than reading about it.
Disclaimer: I'm not a pro youtuber.

@Joseph-Irving
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Joseph-Irving commented Mar 26, 2019

I've opened two new PRs:

Any thoughts or suggestions will be much appreciated.

@michalzxc
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michalzxc commented Oct 9, 2020

What about adding envoy as init container as well? This way it will provide network for other init containers. When init will finish it would 'exit 0' as well, and then regular envoy (not init) would take over

@davinkevin
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davinkevin commented Oct 10, 2020

@michalzxc If I'm not wrong, init containers are executed one by one sequentially, so you currently can't have an envoy next to another container as an init-container.

@rata
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rata commented Oct 12, 2020

Hi!

The sidecar discussion continued on this places (I've updated sig-node slack, github PR that started this and several mailing lists):
https://groups.google.com/g/kubernetes-sig-node/c/w019G3R5VsQ/m/bbRDZTv5CAAJ
https://groups.google.com/g/kubernetes-sig-node/c/7kUaX-jBN3M/m/dhI3E8LOAAAJ

As you can see, we are collecting use cases now, after having some more use cases different small groups can create pre-proposals addressing them. Feel free to add your use case (if it's not there yet) or join later for the pre-proposals part :-)

Please, let's keep this enhacement issue on topic (and probably closed). You are welcome to join the conversation on those places :)

@Joseph-Irving
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Joseph-Irving commented Oct 21, 2020

This KEP will not be progressing, Sig-node and others feel that this is not an incremental step in the right direction so they've gone back to the drawing board and will be coming up with some new KEPs that can hopefully solve all the use cases stated in this KEP as well as others.

Please see @rata's previous comment #753 (comment)
For places where you can contribute to the discussion.

It's unfortunate that all the work done on this KEP will not be getting used, but a wider group of people are now thinking about these issues so hopefully the solution they come up with will be what's best for everyone.
I've already spent over two years trying to get this through so I think this a good time for me to move on, @rata and others will be leading these initiatives going forward.

/close

@k8s-ci-robot
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k8s-ci-robot commented Oct 21, 2020

@Joseph-Irving: Closing this issue.

In response to this:

This KEP will not be progressing, Sig-node and others feel that this is not an incremental step in the right direction so they've gone back to the drawing board and will be coming up with some new KEPs that can hopefully solve all the use cases stated in this KEP as well as others.

Please see @rata's previous comment #753 (comment)
For places where you can contribute to the discussion.

It's unfortunate that all the work done on this KEP will not be getting used, but a wider group of people are now thinking about these issues so hopefully the solution they come up with will be what's best for everyone.
I've already spent over two years trying to get this through so I think this a good time for me to move on, @rata and others will be leading these initiatives going forward.

/close

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

hholst80 added a commit to morecontainers/reloader that referenced this issue Mar 24, 2021
The sidecar stuff was never added into K8s:
kubernetes/enhancements#753 (comment)
@Monokaix
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Monokaix commented Apr 21, 2022

/reopen

@k8s-ci-robot
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k8s-ci-robot commented Apr 21, 2022

@Monokaix: You can't reopen an issue/PR unless you authored it or you are a collaborator.

In response to this:

/reopen

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

@taylorchu
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taylorchu commented Nov 2, 2022

We use in-pod supervisor (https://github.com/taylorchu/wait-for) to solve the sidecar container issue. It is simple and can be used even if you don't use k8s.

@ringerc
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ringerc commented Nov 7, 2022

Another in-pod supervisor designed to work around this infrastructure issue is https://github.com/karlkfi/kubexit

@taylorchu
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taylorchu commented Nov 8, 2022

karlkfi/kubexit is cited in https://github.com/taylorchu/wait-for#other-ideas. We found several race conditions from it during testing. We also used nrmitchi/k8s-controller-sidecars for 1 year, but it cannot keep up if you have >= 1000 short-lived jobs running at the same time. In the end, we decided to write our own tool with a much simpler design.

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