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Can a pod discover its namespace? #9474

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justinsb opened this issue Jun 9, 2015 · 4 comments
Closed

Can a pod discover its namespace? #9474

justinsb opened this issue Jun 9, 2015 · 4 comments
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kind/support Categorizes issue or PR as a support question.

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@justinsb
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justinsb commented Jun 9, 2015

In #9473 I asked if there was an easy way to discover resource limits without querying the API. But maybe I should just be querying the API... It seems easy, except that I don't know how to find my namespace.

I think I can do this:

POD_NAME=`cat /etc/hostname`
NAMESPACE=default # ???
curl http://${KUBERNETES_RO_SERVICE_HOST}:${KUBERNETES_RO_SERVICE_PORT}/api/v1beta3/namespaces/${NAMESPACE}/pods/${POD_NAME}

And then I get everything (labels, resources etc), which is great.

But:

  1. How can I discover my namespace?
  2. Will this continue to be supported? I can imagine that we don't want to give access to the entire cluster state to pods, but hopefully at least same-namespace or self-identity will be allowed.
  3. Is it safe to assume that hostname == pod-name (and if not, is there a way to discover my pod-name)?
@brendandburns brendandburns modified the milestone: v1.0-candidate Jun 9, 2015
@dchen1107
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I filed #9433 yesterday related to pod and namespace and more discussion can be found at: #9356 (comment)

@goltermann goltermann added the kind/support Categorizes issue or PR as a support question. label Jun 9, 2015
@goltermann goltermann modified the milestones: v1.0-post, v1.0-candidate Jun 9, 2015
@justinsb
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@dchen1107: thanks for that link, although I don't know that it applies here. To be clear - I'm inside a container, and I would like to get the pod info that applies to me from the API. I don't know how to get my namespace, nor am I certain that my hostname was always my name.

I did figure out that I could look at my IP, which is my podIP in the API. Sadly I don't think I'm allowed to use that as a fieldSelector ("message": "field label not supported: podIP"), but then I can at least use that to unambiguously figure out which pod I am. It's not great, but it does work!

@derekwaynecarr
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@justinsb - you can get the namespace information from the downward API.

see the example here:

https://github.com/GoogleCloudPlatform/kubernetes/blob/master/docs/downward_api.md

Closing the issue, re-open if this did not address your concern.

@justinsb
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Thanks @derekwaynecarr - that is a good option that I wasn't aware of!

I was hoping for something that didn't require the manifest writer to do anything, but maybe that's over-optimizing. (I'm thinking about packaged k8s apps that can just be deployed and will self-configure, but it'll probably involve a service & and an rc anyway so this would actually work great).

Between this and the option of querying the k8s API I have some reasonable options!

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@justinsb @brendandburns @derekwaynecarr @dchen1107 @goltermann