145 lines
3.7 KiB
Plaintext
145 lines
3.7 KiB
Plaintext
A memory request is a configuration that sets the guaranteed amount of memory that a
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container will be able to use. It is part of the resource management functionality of
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Kubernetes, which allows for the control and allocation of computational
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resources to containers.
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When a memory request is set for a container, Kubernetes will only schedule it on a node that can give it that resource,
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thereby guaranteeing that the container can use the specified requested memory.
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== Why is this an issue?
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Without a memory request, a container can potentially be scheduled on a node where
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there are not enough resources for it. This can lead to unpredictable behavior of the container and the node itself.
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=== What is the potential impact?
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==== Unpredictable Resource Allocation
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Without defined requests, Kubernetes doesn't know how much of a particular resource
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to allocate to a container. This can lead to unpredictable behavior, as the Kubernetes scheduler may
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not make optimal decisions about pod placement and resource contention management.
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For instance, a container might not get the resources it needs to function correctly, leading to
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performance issues or even failure of the container.
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==== System Instability
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In the worst-case scenario, if a container uses more resources than a node can
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handle (due to lack of defined requests), it can cause the node to run out of
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resources. This can lead to system instability, and in extreme cases, the node
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might crash, causing downtime for all containers running on that node.
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== How to fix it
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=== Code examples
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To avoid potential issues, either specify a memory request for each container in a pod specification
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or create a resource of a kind, `LimitRange`,
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that sets a default memory request for all containers in all pod specifications belonging to the same namespace.
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==== Noncompliant code example
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[source,yaml,diff-id=1,diff-type=noncompliant]
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----
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apiVersion: v1
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kind: Pod
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metadata:
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name: example
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spec:
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containers:
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- name: web # Noncompliant
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image: nginx
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----
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[source,yaml,diff-id=2,diff-type=noncompliant]
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----
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apiVersion: v1
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kind: Pod
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metadata:
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name: example
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spec:
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containers:
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- name: web # Noncompliant
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image: nginx
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----
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==== Compliant solution
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[source,yaml,diff-id=1,diff-type=compliant]
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----
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apiVersion: v1
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kind: Pod
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metadata:
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name: example
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spec:
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containers:
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- name: web
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image: nginx
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resources:
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requests:
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memory: 100Mi
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----
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[source,yaml,diff-id=2,diff-type=compliant]
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----
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apiVersion: v1
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kind: LimitRange
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metadata:
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name: mem-limit-range
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namespace: default-mem-example
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spec:
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limits:
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- type: Container
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defaultRequest:
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memory: 100Mi
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---
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apiVersion: v1
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kind: Pod
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metadata:
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name: example
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namespace: default-mem-example
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spec:
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containers:
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- name: web
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image: nginx
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----
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=== How does this work?
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A request can be set through the property `resources.requests.memory` of a
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container. Alternatively, a default request for a namespace can be set with
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`LimitRange` through `spec.limits[].defaultRequest.memory`.
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== Resources
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=== Documentation
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* Kubernetes Documentation - https://kubernetes.io/docs/tasks/administer-cluster/manage-resources/memory-default-namespace/[Configure Default Memory Requests and Limits for a Namespace]
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=== Articles & blog posts
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* Google Cloud Blog - https://cloud.google.com/blog/products/containers-kubernetes/kubernetes-best-practices-resource-requests-and-limits[Kubernetes best practices: Resource requests and limits]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Specify a memory request for this container.
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=== Highlighting
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* Highlight the key of the first child of the container that does not specify a memory request.
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endif::env-github,rspecator-view[]
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