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61 lines
2.7 KiB
Plaintext
61 lines
2.7 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * nodes/nodes-cluster-overcommit.adoc
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// * post_installation_configuration/node-tasks.adoc
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:_mod-docs-content-type: CONCEPT
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[id="nodes-cluster-overcommit-reserving-memory_{context}"]
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= Understanding compute resources and containers
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The node-enforced behavior for compute resources is specific to the resource
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type.
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[id="understanding-container-CPU-requests_{context}"]
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== Understanding container CPU requests
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A container is guaranteed the amount of CPU it requests and is additionally able
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to consume excess CPU available on the node, up to any limit specified by the
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container. If multiple containers are attempting to use excess CPU, CPU time is
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distributed based on the amount of CPU requested by each container.
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For example, if one container requested 500m of CPU time and another container
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requested 250m of CPU time, then any extra CPU time available on the node is
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distributed among the containers in a 2:1 ratio. If a container specified a
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limit, it will be throttled not to use more CPU than the specified limit.
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CPU requests are enforced using the CFS shares support in the Linux kernel. By
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default, CPU limits are enforced using the CFS quota support in the Linux kernel
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over a 100ms measuring interval, though this can be disabled.
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[id="understanding-memory-requests-container_{context}"]
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== Understanding container memory requests
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A container is guaranteed the amount of memory it requests. A container can use
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more memory than requested, but once it exceeds its requested amount, it could
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be terminated in a low memory situation on the node.
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If a container uses less memory than requested, it will not be terminated unless
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system tasks or daemons need more memory than was accounted for in the node's
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resource reservation. If a container specifies a limit on memory, it is
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immediately terminated if it exceeds the limit amount.
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////
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Not in 4.1
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[id="containers-ephemeral_{context}"]
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== Understanding containers and ephemeral storage
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[NOTE]
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====
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The {product-title} cluster uses ephemeral storage to store information that does not have to persist after the cluster is destroyed.
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====
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A container is guaranteed the amount of ephemeral storage it requests. A
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container can use more ephemeral storage than requested, but once it exceeds its
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requested amount, it can be terminated if the available ephemeral disk space gets
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too low.
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If a container uses less ephemeral storage than requested, it will not be
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terminated unless system tasks or daemons need more local ephemeral storage than
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was accounted for in the node's resource reservation. If a container specifies a
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limit on ephemeral storage, it is immediately terminated if it exceeds the limit
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amount.
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////
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