The expression 0.1 is equivalent to the expression 100m, which can be read as “one hundred millicpu”. A Container with .cpu of 0.5 is guaranteed half as much CPU as one that asks for 1 CPU. One cpu, in Kubernetes, is equivalent to 1 vCPU/Core for cloud providers and 1 hyperthread on bare-metal Intel processors.įractional requests are allowed. Limits and requests for CPU resources are measured in cpu units. Resource units in Kubernetes Meaning of CPU A Pod resource request/limit for a particular resource type is the sum of the resource requests/limits of that type for each Container in the Pod. .hugepages-Īlthough requests and limits can only be specified on individual Containers, it is convenient to talk about Pod resource requests and limits.Resource requests and limits of Pod and ContainerĮach Container of a Pod can specify one or more of the following: API resources, such as Pods and Services are objects that can be read and modified through the Kubernetes API server. Compute resources are measurable quantities that can be requested, allocated, and consumed. This is different from the memory and cpu resources.ĬPU and memory are collectively referred to as compute resources, or resources. Note: You cannot overcommit hugepages-* resources. If the container tries allocating over 40 2MiB huge pages (a total of 80 MiB), that allocation fails. Huge pages are a Linux-specific feature where the node kernel allocates blocks of memory that are much larger than the default page size.įor example, on a system where the default page size is 4KiB, you could specify a limit, hugepages-2Mi: 80Mi. If you’re using Kubernetes v1.14 or newer, you can specify huge page resources. CPU represents compute processing and is specified in units of Kubernetes CPUs. Resource typesĬPU and memory are each a resource type. Similarly, if a Container specifies its own CPU limit, but does not specify a CPU request, Kubernetes automatically assigns a CPU request that matches the limit. Note: If a Container specifies its own memory limit, but does not specify a memory request, Kubernetes automatically assigns a memory request that matches the limit. Different runtimes can have different ways to implement the same restrictions. Limits can be implemented either reactively (the system intervenes once it sees a violation) or by enforcement (the system prevents the container from ever exceeding the limit). For example: when a process in the container tries to consume more than the allowed amount of memory, the system kernel terminates the process that attempted the allocation, with an out of memory (OOM) error. The runtime prevents the container from using more than the configured resource limit. If you set a memory limit of 4GiB for that Container, the kubelet (and container runtime) enforce the limit. However, a container is not allowed to use more than its resource limit.įor example, if you set a memory request of 256 MiB for a container, and that container is in a Pod scheduled to a Node with 8GiB of memory and no other Pods, then the container can try to use more RAM. 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. The kubelet also reserves at least the request amount of that system resource specifically for that container to use. When you specify a resource limit for a Container, the kubelet enforces those limits so that the running container is not allowed to use more of that resource than the limit you set. When you specify the resource request for Containers in a Pod, the scheduler uses this information to decide which node to place the Pod on. The most common resources to specify are CPU and memory (RAM) there are others. When you specify a Pod, you can optionally specify how much of each resource a Container needs.
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