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Cloud and Container Basics

A node has allocatable resources of 4 CPU cores and 8 GiB of memory. Each Pod's container has requests of 500m CPU and 1.5 GiB memory and limits of 1 CPU core and 2 GiB memory. There are no other Pods and no system reservations. Which of the following is the maximum number of Pods that can be placed on this node?

  1. A4
  2. B5
  3. C8
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Answer: B. 5

The scheduler places Pods so that the sum of the requests of the Pods on a node does not exceed the allocatable amount, for CPU and for memory separately. CPU allows up to 4000m ÷ 500m = 8 Pods, but memory allows 8 ÷ 1.5 = 5.33…, that is, up to 5. Both conditions must hold, so the answer is 5. Limits are not used for placement, so the limits of the 5 Pods add up to 5 CPU cores and 10 GiB of memory, more than the node has, and resources run short if all Pods use their maximum at the same time.

  • A. This is the value computed from limits (CPU 4 ÷ 1 = 4, memory 8 ÷ 2 = 4). Placement is decided by requests.
  • B. Correct. CPU allows 8 Pods and memory 5, so the smaller number, 5, applies.
  • C. This uses only the CPU requests. The total memory requests must also fit within 8 GiB.
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