Kubernetes CPU Resource Requests at Runtime

When you create a Pod, the Kubernetes scheduler selects a node for the Pod to run on. Each node has a maximum capacity for each of the resource types: the amount of CPU and memory it can provide for Pods. The scheduler ensures that, for each resource type, the sum of the resource requests of the scheduled Containers is less than the capacity of the node. Note that although actual memory or CPU resource usage on nodes is very low, the scheduler still refuses to place a Pod on a node if the capacity check fails. This protects against a resource shortage on a node when resource usage later increases, for example, during a daily peak in request rate.

If the node where a Pod is running has enough of a resource available, it’s possible (and allowed) for a container to use more resource than its request for that resource specifies. However, a container is not allowed to use more than its resource limit.

The CPUShares value provides tasks in a cgroup with a relative amount of CPU time. Once the system has mounted the cpu cgroup controller, you can use the file cpu.shares to define the number of shares allocated to the cgroup. CPU time is determined by dividing the cgroup’s CPUShares by the total number of defined CPUShares on the system.

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