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Let's suppose i have 5 k8s nodes with 2 cpu on each node.

This mean i have 10 cpus.

Now let's suppose i want to deploy a very small and basic application with 20 replicas.

Is there a limitation on k8s that will allow only one pod for one cpu and reject 10/20 replicas ?

Thanks

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In addition to the good answer by @therianthropie, here are useful notes to help you understand the situation better.:

  • You can set requests and limits very arbitrarily (and yes, as fractions of a CPU and very small amounts of memory).
  • Kubernetes will not do its job well if you don't get real values for these.
  • If you under-shoot your request, kubernetes will schedule a lot of apps without requesting enough resources and you'll have problems with the CPU/memory/disk, and so on.
  • If you over-shoot your request a lot, your kubernetes nodes may be doing virtually nothing.
  • Some apps are very CPU bound, some memory bound, some use virtually no resources. So, you really can't guess.
  • Prometheus is a popular tool that you can install into kubernetes with basically a single command.
  • You can chart things in grafana.
  • So, then you choose your arbitrary values, then watch the charts as you use the app, and then you can adjust them to something sane / useful so kubernetes can do its job well. You can also set alerts with something called alert manager if your values are too ridiculous (it's a good idea once you're ready).
  • Note - requests are what kubernetes allocates for your pod. Limits are the max resources your pod can spike to when it needs them. There is a general assumption that not all pods will spike in usage at once / or over a long term or else this idea would not work.
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No, you can set requests and limits with fractions of vCPUs. For example, every pod has a request/limit of 100m (1/10 of a CPU). This means 20 pods would need 2 CPUs in total.

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