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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
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35 changes: 35 additions & 0 deletions docs/modules/hbase/pages/usage-guide/operations/pod-placement.adoc
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Expand Up @@ -3,6 +3,16 @@

You can configure Pod placement for HBase nodes as described in xref:concepts:operations/pod_placement.adoc[].

== Defaults

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 across nodes so multiple instances don't end up on the same Kubernetes node (masters, regionservers, rest servers) (weight 70)

Check notice on line 12 in docs/modules/hbase/pages/usage-guide/operations/pod-placement.adoc

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[LanguageTool] docs/modules/hbase/pages/usage-guide/operations/pod-placement.adoc#L12 

Use a comma before ‘so’ if it connects two independent clauses (unless they are closely connected and short). (COMMA_COMPOUND_SENTENCE_2[1])
Suggestions: `, so`
URL: https://languagetool.org/insights/post/comma-before-and/ 
Rule: https://community.languagetool.org/rule/show/COMMA_COMPOUND_SENTENCE_2?lang=en-US&subId=1
Category: PUNCTUATION
Raw output 
docs/modules/hbase/pages/usage-guide/operations/pod-placement.adoc:12:56: Use a comma before ‘so’ if it connects two independent clauses (unless they are closely connected and short). (COMMA_COMPOUND_SENTENCE_2[1])
 Suggestions: `, so`
 URL: https://languagetool.org/insights/post/comma-before-and/ 
 Rule: https://community.languagetool.org/rule/show/COMMA_COMPOUND_SENTENCE_2?lang=en-US&subId=1
 Category: PUNCTUATION

NOTE: All default affinities are only preferred and not enforced, as we can not expect all setups to have multiple Kubernetes nodes. If you want to have them enforced, you need to specify you own `requiredDuringSchedulingIgnoredDuringExecution` affinities.

Default Pod placement constraints for master nodes:

[source,yaml]
Expand Down Expand Up @@ -94,3 +104,28 @@
In the examples above `cluster-name` is the name of the HBase custom resource that owns this Pod. The `hdfs-cluster-name` is the name of the HDFS cluster that was configured in the `hdfsConfigMapName` property.

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
For general configuration of Pod placement, see the xref:concepts:operations/pod_placement.adoc[Pod placement concepts] page.
One example use-case for HBase would be to *require* the HBase masters to run on different Kubernetes nodes as follows:

[source,yaml]
----
spec:
masters:
config:
affinity:
podAntiAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
- labelSelector:
matchLabels:
app.kubernetes.io/name: hbase
app.kubernetes.io/instance: cluster-name # Replace with you HbaseCluster name!
app.kubernetes.io/component: master
topologyKey: kubernetes.io/hostname
roleGroups:
default:
replicas: 2
----

WARNING: Please note that the Pods will be stuck in `Pending`, when your Kubernetes cluster does not have any node without a masters already running on it and sufficient compute resources.