feat(common): Allow configuring default topologyKey (#32461)

**Description**
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Please include a summary of the change and which issue is fixed. Please
also include relevant motivation and context. List any dependencies that
are required for this change.
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This PR adds a global option to control the default topologyKey used for
topologySpreadConstraints

⚒️ Fixes  #32457

**⚙️ Type of change**

- [x] ⚙️ Feature/App addition
- [ ] 🪛 Bugfix
- [ ] ⚠️ Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 🔃 Refactor of current code
- [ ] 📜 Documentation Changes

**🧪 How Has This Been Tested?**
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Please describe the tests that you ran to verify your changes. Provide
instructions so we can reproduce. Please also list any relevant details
for your test configuration
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Ran the common library unit tests, added one to verify the usage of the
field

**📃 Notes:**
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**✔️ Checklist:**

- [x] ⚖️ My code follows the style guidelines of this project
- [x] 👀 I have performed a self-review of my own code
- [x] #️⃣ I have commented my code, particularly in hard-to-understand
areas
- [x] 📄 I have made changes to the documentation
- [x] 🧪 I have added tests to this description that prove my fix is
effective or that my feature works
- [x] ⬆️ I increased versions for any altered app according to semantic
versioning
- [x] I made sure the title starts with `feat(chart-name):`,
`fix(chart-name):`, `chore(chart-name):`, `docs(chart-name):` or
`fix(docs):`

**➕ App addition**

If this PR is an app addition please make sure you have done the
following.

- [ ] 🖼️ I have added an icon in the Chart's root directory called
`icon.png`

---

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charts/library/common-test/Chart.yaml

@@ -7,7 +7,7 @@ apiVersion: v2
 appVersion: unknown
 dependencies:
   - name: common
-    version: ~26.3.0
+    version: ~26.4.0
     repository: file://../common/
     condition: ""
     alias: ""

charts/library/common-test/tests/pod/topologySpreadConstraints.yaml

@@ -120,6 +120,40 @@ tests:
               topologyKey: truecharts.org/test
               whenUnsatisfiable: ScheduleAnyway
 
+  - it: should pass with topologyKey from "global"
+    set:
+      global:
+        fallbackDefaults:
+          topologyKey: "truecharts.org/test"
+      workload:
+        workload-name1:
+          enabled: true
+          primary: true
+          type: Deployment
+          podSpec: {}
+    asserts:
+      - documentIndex: *deploymentDoc
+        equal:
+          path: spec.selector.matchLabels
+          value:
+            app.kubernetes.io/instance: test-release-name
+            app.kubernetes.io/name: common-test
+            pod.name: workload-name1
+      - documentIndex: *deploymentDoc
+        equal:
+          path: spec.template.spec.topologySpreadConstraints
+          value:
+            - labelSelector:
+                matchLabels:
+                  app.kubernetes.io/instance: test-release-name
+                  app.kubernetes.io/name: common-test
+                  pod.name: workload-name1
+              maxSkew: 1
+              nodeAffinityPolicy: Honor
+              nodeTaintsPolicy: Honor
+              topologyKey: truecharts.org/test
+              whenUnsatisfiable: ScheduleAnyway
+
   - it: should pass with multiple topologySpreadConstraints from "pod"
     set:
       podOptions:

charts/library/common/Chart.yaml

@@ -48,4 +48,4 @@ sources:
   - https://hub.docker.com/_/
   - https://hub.docker.com/r/mikefarah/yq
 type: library
-version: 26.3.0
+version: 26.4.0

charts/library/common/templates/lib/pod/_topologySpreadConstraints .tpl

@@ -24,7 +24,7 @@ objectData: The object data to be used to render the Pod.
   {{- if and (mustHas $objectData.type $validTypes) $rootCtx.Values.podOptions.defaultSpread }}
 - maxSkew: 1
   whenUnsatisfiable: ScheduleAnyway
-  topologyKey: "kubernetes.io/hostname"
+  topologyKey: {{ default "kubernetes.io/hostname" $rootCtx.Values.global.fallbackDefaults.topologyKey }}
   labelSelector:
     matchLabels:
       {{- include "tc.v1.common.lib.metadata.selectorLabels" (dict "rootCtx" $rootCtx "objectType" "pod" "objectName" $objectData.shortName) | indent 6 }}

charts/library/common/values.yaml

@@ -57,6 +57,9 @@ global:
     # will be used for all CNPG objects
     # Can be overruled per CNPG objects
     pgVersion: 16
+    # -- Define a topologyKey for default topologySpreadConstraints
+    # Will be used when defaultSpread: true
+    topologyKey: kubernetes.io/hostname
   metallb:
     # -- Adds metalLB annotations to services
     addServiceAnnotations: true

website/src/content/docs/common/fallbackDefaults.md

@@ -48,6 +48,7 @@ fallbackDefaults:
       timeoutSeconds: 2
       failureThreshold: 60
       successThreshold: 1
+  topologyKey: kubernetes.io/hostname
 ```
 
 ## `probeType`
@@ -779,6 +780,22 @@ fallbackDefaults:
       successThreshold: 1
 ```
 
+---
+
+## `topologyKey`
+
+Define default topologyKey for topologySpreadConstraints in podOptions
+
+
+|            |                                |
+| ---------- | ------------------------------ |
+| Key        | `fallbackDefaults.topologyKey` |
+| Type       | `string`                          |
+| Required   | ❌                             |
+| Helm `tpl` | ❌                             |
+| Default    | `kubernetes.io/hostname`                            |
+
+
 ---
 
 ## Full Examples
@@ -808,4 +825,5 @@ fallbackDefaults:
       timeoutSeconds: 2
       failureThreshold: 60
       successThreshold: 1
+  topologyKey: truecharts.org/example
 ```