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Resolve formatting issue and add example for node affinity example.

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Robert Van Voorhees 2021-10-24 06:06:43 -04:00
parent b7e1c2a041
commit 489e938f1c
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1 changed files with 33 additions and 31 deletions
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38
content/en/docs/concepts/workloads/pods/pod-topology-spread-constraints.md
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@ -234,10 +234,12 @@ To overcome this situation, you can either increase the `maxSkew` or modify one
The scheduler will skip the non-matching nodes from the skew calculations if the incoming Pod has `spec.nodeSelector` or `spec.affinity.nodeAffinity` defined.
### Example: TopologySpreadConstraints with NodeAffinity
Suppose you have a 5-node cluster ranging from zoneA to zoneC:
{{<mermaid>}}
graph BT
{{<mermaid>}}
graph BT
subgraph "zoneB"
p3(Pod) --> n3(Node3)
n4(Node4)
@ -247,30 +249,30 @@ Suppose you have a 5-node cluster ranging from zoneA to zoneC:
p2(Pod) --> n2(Node2)
end
classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
class n1,n2,n3,n4,p1,p2,p3 k8s;
class p4 plain;
class zoneA,zoneB cluster;
{{< /mermaid >}}
classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
class n1,n2,n3,n4,p1,p2,p3 k8s;
class p4 plain;
class zoneA,zoneB cluster;
{{< /mermaid >}}
{{<mermaid>}}
graph BT
{{<mermaid>}}
graph BT
subgraph "zoneC"
n5(Node5)
end
classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
class n5 k8s;
class zoneC cluster;
{{< /mermaid >}}
classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
class n5 k8s;
class zoneC cluster;
{{< /mermaid >}}
and you know that "zoneC" must be excluded. In this case, you can compose the yaml as below, so that "mypod" will be placed onto "zoneB" instead of "zoneC". Similarly `spec.nodeSelector` is also respected.
{{< codenew file="pods/topology-spread-constraints/one-constraint-with-nodeaffinity.yaml" >}}
{{< codenew file="pods/topology-spread-constraints/one-constraint-with-nodeaffinity.yaml" >}}
The scheduler doesn't have prior knowledge of all the zones or other topology domains that a cluster has. They are determined from the existing nodes in the cluster. This could lead to a problem in autoscaled clusters, when a node pool (or node group) is scaled to zero nodes and the user is expecting them to scale up, because, in this case, those topology domains won't be considered until there is at least one node in them.