kubernetes 为什么AKS节点在实际内存仍然可用的情况下显示的可分配内存量较少

fcwjkofz 于 2023-06-21 发布在 Kubernetes

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我想知道AKS节点在预留内存时考虑的因素以及它是如何计算可分配内存的。
在我的集群中，我们有多个节点（2 CPU，7 GB RAM）。
我观察到的是，所有节点（18+）在7 GB中只显示了4GB的可分配内存。因此，我们的群集具有用于新部署的资源连接。因此，我们必须相应地增加节点数量以满足资源需求。

已更新，如我在下面添加kubectl top node命令的评论。这里很奇怪，节点消耗%如何超过100%。

NAME                                CPU(cores)   CPU%   MEMORY(bytes)   MEMORY%
aks-nodepool1-xxxxxxxxx-vmssxxxx00   265m         13%    2429Mi          53%
aks-nodepool1-xxxxxxxxx-vmssxxxx01   239m         12%    3283Mi          71%
aks-nodepool1-xxxxxxxxx-vmssxxxx0g   465m         24%    4987Mi          109%
aks-nodepool2-xxxxxxxxx-vmssxxxx8i   64m          3%     3085Mi          67%
aks-nodepool2-xxxxxxxxx-vmssxxxx8p   114m         6%     5320Mi          116%
aks-nodepool2-xxxxxxxxx-vmssxxxx9n   105m         5%     2715Mi          59%
aks-nodepool2-xxxxxxxxx-vmssxxxxaa   134m         7%     5216Mi          114%
aks-nodepool2-xxxxxxxxx-vmssxxxxat   179m         9%     5498Mi          120%
aks-nodepool2-xxxxxxxxx-vmssxxxxaz   141m         7%     4769Mi          104%
aks-nodepool2-xxxxxxxxx-vmssxxxxb0   72m          3%     1972Mi          43%
aks-nodepool2-xxxxxxxxx-vmssxxxxb1   133m         7%     3684Mi          80%
aks-nodepool2-xxxxxxxxx-vmssxxxxb3   182m         9%     5294Mi          115%
aks-nodepool2-xxxxxxxxx-vmssxxxxb4   133m         7%     5009Mi          109%
aks-nodepool2-xxxxxxxxx-vmssxxxxbj   68m          3%     1783Mi          39%

因此，这里我以aks-nodepool 2-xxxxxxxxx-vmssxxxx 8 p 114 m 6% 5320 Mi 116%节点为例
我计算了该节点中每个pod的内存使用量，总共约为4.1GB，节点可分配内存为4.6GB，实际为7 GB。
这里“为什么顶部节点”的输出与该节点中每个pod的“顶部pod输出”不相同？
预期% == 4.1GB/4.6 GB== 93%，但顶级节点命令的输出为116%

kubernetes

来源：https://stackoverflow.com/questions/68521392/why-aks-nodes-shows-less-amount-of-memory-as-allocatable-where-its-actual-memory

2条答案

按热度按时间

jdgnovmf1#

这是AKS保持群集安全和正常运行的预期行为。
当您在AKS中创建k8s集群时，并不意味着您将获得VM拥有的所有内存/CPU。根据群集配置的不同，它消耗的资源甚至可能超过您共享的资源。例如，如果您启用OMS代理以获得AKS的洞察，则它也将保留一些容量。
从官方文档中，Azure Kubernetes Service（AKS）的Kubernetes核心概念-->资源保留。有关相关的最佳实践，请参阅Best practices for basic scheduler features in AKS。

AKS uses node resources to help the node function as part of your cluster. This usage can create a discrepancy between your node's total resources and the allocatable resources in AKS. Remember this information when setting requests and limits for user deployed pods.

To find a node's allocatable resources, run:
kubectl describe node [NODE_NAME]

To maintain node performance and functionality, AKS reserves resources on each node. As a node grows larger in resources, the resource reservation grows due to a higher need for management of user-deployed pods.

Two types of resources are reserved:
- CPU
    Reserved CPU is dependent on node type and cluster configuration, which may cause less allocatable CPU due to running additional features.
- Memory
    Memory utilized by AKS includes the sum of two values.
    
    - kubelet daemon
    The kubelet daemon is installed on all Kubernetes agent nodes to manage container creation and termination.
    By default on AKS, kubelet daemon has the memory.available<750Mi eviction rule, ensuring a node must always have at least 750 Mi allocatable at all times. When a host is below that available memory threshold, the kubelet will trigger to terminate one of the running pods and free up memory on the host machine.
    
    - A regressive rate of memory reservations for the kubelet daemon to properly function (kube-reserved).
    25% of the first 4 GB of memory
    20% of the next 4 GB of memory (up to 8 GB)
    10% of the next 8 GB of memory (up to 16 GB)
    6% of the next 112 GB of memory (up to 128 GB)
    2% of any memory above 128 GB
    
Memory and CPU allocation rules:
- Keep agent nodes healthy, including some hosting system pods critical to cluster health.
- Cause the node to report less allocatable memory and CPU than it would if it were not part of a Kubernetes cluster.
The above resource reservations can't be changed.

For example, if a node offers 7 GB, it will report 34% of memory not allocatable including the 750Mi hard eviction threshold.

0.75 + (0.25*4) + (0.20*3) = 0.75GB + 1GB + 0.6GB = 2.35GB / 7GB = 33.57% reserved

In addition to reservations for Kubernetes itself, the underlying node OS also reserves an amount of CPU and memory resources to maintain OS functions.

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hmae6n7t2#

这不是AKS特有的。kubectl top node根据可分配内存和CPU计算百分比

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