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docs: Add example to pod placement #413

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Nov 14, 2023
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docs: Add example to pod placement #413

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docs: Add example to pod placement
sbernauer Nov 7, 2023
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typo
sbernauer Nov 7, 2023
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sbernauer Nov 8, 2023
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sbernauer Nov 8, 2023
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docs
sbernauer Nov 8, 2023
e0ce50b
fix lower and upper case
sbernauer Nov 8, 2023
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docs
sbernauer Nov 8, 2023
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Update docs/modules/hbase/pages/usage-guide/operations/pod-placement.…
sbernauer Nov 13, 2023
30eba1a
clarify defaults are only prefered
sbernauer Nov 13, 2023
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Merge branch 'main' into docs/improve-pod-placement
sbernauer Nov 13, 2023
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8 changes: 4 additions & 4 deletions docs/modules/hbase/pages/usage-guide/operations/pod-placement.adoc
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Expand Up @@ -7,9 +7,9 @@ You can configure Pod placement for HBase nodes as described in xref:concepts:op

The default affinities created by the operator are:

1. Co-locate all the Hbase Pods (weight 20)
2. Co-locate Hbase regionservers with the underlying HDFS datanodes (weight 50)
3. Distribute all Pods within the same role (masters, region servers, rest servers) (weight 70)
1. Co-locate all the HBase Pods (weight 20)
2. Co-locate HBase regionservers with the underlying HDFS datanodes (weight 50)
3. Distribute all Pods within the same role (masters, regionservers, rest servers) (weight 70)
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Sorry, reading this again now, I have a new suggestion.

Suggested change
1. Co-locate all the HBase Pods (weight 20)
2. Co-locate HBase regionservers with the underlying HDFS datanodes (weight 50)
3. Distribute all Pods within the same role (masters, regionservers, rest servers) (weight 70)
1. Co-locate all the HBase Pods (weight 20)
2. Co-locate HBase regionservers with the underlying HDFS datanodes (weight 50)
3. Distribute all Pods within the same role across nodes so multiple instances don't end up on the same Kubernetes node (masters, regionservers, rest servers) (weight 70)

Point 1 needs clarification but I don't know exactly how. What is it we do exactly there?
And we should point out (I thought we did somewhere) that this is "only" preferred not required

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See 30eba1a

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Thank you. But what does the first point actually mean?
"Co-locate al the HBase Pods"

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Its the first rule in the example below

affinity:
  podAffinity:
    preferredDuringSchedulingIgnoredDuringExecution:
    - podAffinityTerm:
        labelSelector:
          matchLabels:
            app.kubernetes.io/instance: cluster-name
            app.kubernetes.io/name: hbase
        topologyKey: kubernetes.io/hostname
      weight: 20
  podAntiAffinity:
    preferredDuringSchedulingIgnoredDuringExecution:
    - podAffinityTerm:
        labelSelector:
          matchLabels:
            app.kubernetes.io/component: master
            app.kubernetes.io/instance: cluster-name
            app.kubernetes.io/name: hbase
        topologyKey: kubernetes.io/hostname
      weight: 70

I just pulls all HBase Pods together, so that e.g. hbase master + regionserver + restserver run on the same node to reduce latency.


Default Pod placement constraints for master nodes:

Expand Down Expand Up @@ -104,7 +104,7 @@ In the examples above `cluster-name` is the name of the HBase custom resource th
NOTE: It is important that the `hdfsConfigMapName` property contains the name the HDFS cluster. You could instead configure ConfigMaps of specific name or data roles, but for the purpose of pod placement, this will lead to faulty behavior.

== Use custom pod placement
xref:concepts:operations/pod_placement.adoc[] describes how you can configure pod placement in general.
xref:concepts:operations/pod_placement.adoc[The concepts page on Pod Placement] describes how you can configure pod placement in general.
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@lfrancke lfrancke Nov 8, 2023 •
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I'm sorry but: How does this look in a rendered version now?
I wanted to avoid the duplication of "Pod placement"
And: It should be "placement" not "Placement"

And: You have "Pod" once and "pod" another time. We should be consistent

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Fixed lower and upper case.

Currently it reads

The concepts page on Pod placement describes how you can configure Pod placement in general.

We could change it to e.g.

This concepts page describes how you can configure Pod placement in general.

but I have been told to not have "click this" links, but instead tell the user where the link is pointing too.
But I don't have a strong opinion and let you decide

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My suggestion:

For general configuration of Pod placement, see the [Pod placement concepts] page.

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Applied in 2996c2f

One example use-case for HBase would be to *require* the HBase masters to run on different Kubernetes nodes as follows:

[source,yaml]
Expand Down