From 438459d9bcb7cb6cff3407d5baa96ecb602a267d Mon Sep 17 00:00:00 2001
From: Guillaume VARA <guillaume.vara@gmail.com>
Date: Wed, 19 Jun 2024 18:35:45 +0200
Subject: [PATCH] Create application-sets.md

Signed-off-by: Guillaume VARA <guillaume.vara@gmail.com>
---
 docs/configuration/application-sets.md | 78 ++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 docs/configuration/application-sets.md

diff --git a/docs/configuration/application-sets.md b/docs/configuration/application-sets.md
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+# ApplicationSet considerations
+
+If using an `ApplicationSet` instead of `Application`, there are a few things to consider. Take this `ApplicationSet` manifest as example:
+
+```yaml
+apiVersion: argoproj.io/v1alpha1
+kind: ApplicationSet
+metadata:
+  name: vitrine
+  namespace: argocd
+spec:
+  ignoreApplicationDifferences:
+    - jsonPointers:
+      - /spec/source/helm/parameters
+  goTemplate: true
+  goTemplateOptions: ["missingkey=error"]
+  generators:
+  - matrix:
+      generators:
+      - list:
+          elements:
+          - name: vitrine
+      - list:
+          elements:
+          - branch: main
+          - branch: develop
+  template:
+    metadata:
+      name: "{{ printf `%s-%s` `{{ .name }}` `{{ .branch }}` }}"
+      namespace: argocd
+      annotations:
+        #
+        argocd-image-updater.argoproj.io/image-list: "{{ `{{ .name }}` }}=docker.io/myuser/{{ `{{ .name }}` }}:{{ `{{ .branch }}` }}"
+        argocd-image-updater.argoproj.io/{{ `{{ .name }}` }}.helm.image-name: config.image.name
+        argocd-image-updater.argoproj.io/{{ `{{ .name }}` }}.helm.image-tag: config.image.tag
+        argocd-image-updater.argoproj.io/{{ `{{ .name }}` }}.update-strategy: digest
+    spec:
+      destination:
+        server: {{ quote .Values.spec.destination.server }}
+        namespace: "{{ printf `%s-%s` .Values.sharedConfig.namespaceBase `{{ .branch }}` }}"
+      project: default
+      syncPolicy:
+        automated: {}
+        syncOptions:
+        - CreateNamespace=true
+      source:
+        path: "{{ printf `%s/%s` .Values.spec.source.repo.paths.charts `{{ .name }}` }}"
+        repoURL: {{ include "repoNameFullName" . }}
+        targetRevision: HEAD
+        helm:
+          valueFiles:
+          - values.yaml
+          valuesObject:
+            config:
+              image:
+                name: "docker.io/myuser//{{ `{{ .name }}` }}"
+                tag: "{{ `{{ .branch }}` }}"
+```
+
+## Automatic patching of children `Application`s
+
+By default, `ApplicationSet` prevents any manual modification of spawned `Application`. For example, if you try to update a child `Application` through the UI, the modification will be instantly reverted; this is an expected behavior. 
+Theses rejected manual modifications sadly include Image Updater's `spec.template.spec.source.helm.parameters` `Application` automatic patching, which will prevent `argocd-image-updater.argoproj.io/write-back-method: argocd` implicit behavior to function properly.
+
+In this case, you will still receive `ImagesUpdated` events on your affected `Application`, but Image Updater will continously retry again, to no avail.
+
+To allow Image Updater to work here, you need to add this to your `ApplicationSet`:
+
+```yaml
+spec:
+  ignoreApplicationDifferences:
+    - jsonPointers:
+      - /spec/source/helm/parameters
+```
+
+This will prevent automatic revert behavior of `ApplicationSet` if any of the defined `jsonPointers` subjacent values are altered on children `Application`.
+
+Please mind there are also a few caveats to consider. (see https://argo-cd.readthedocs.io/en/stable/operator-manual/applicationset/Controlling-Resource-Modification/#limitations-of-ignoreapplicationdifferences)