docs: add documentation for the limitation

Signed-off-by: chansuke <[email protected]>

Author: chansuke

docs/index.md

@@ -96,6 +96,12 @@ Otherwise, current known limitations are:
   Image Updater is running in (or has access to). It is currently not possible
   to fetch those secrets from other clusters.
 
+* When using Helm applications with zero-replica deployments and `force-update`
+  enabled, the image updater will attempt to match common Helm parameter patterns
+  for image tags (such as `image.tag`, `*.version`, `*.imageTag`). If your Helm
+  chart uses uncommon parameter names, the updater may not detect the current
+  image version correctly, leading to repeated update attempts.
+
 ## Questions, help and support
 
 If you have any questions, need some help in setting things up or just want to

pkg/argocd/argocd.go

@@ -736,7 +736,10 @@ func (a ApplicationType) String() string {
 	}
 }
 
-// getImageFromSpec tries to find the current image tag from the application spec
+// getImageFromSpec tries to find the current image tag from the application spec.
+// For Helm applications, it attempts to match common parameter patterns for image tags
+// using regex (e.g., image.tag, *.version, *.imageTag). However, if a Helm chart uses
+// uncommon parameter names, this function may not detect them correctly.
 func getImageFromSpec(app *v1alpha1.Application, targetImage *image.ContainerImage) *image.ContainerImage {
 	appType := getApplicationType(app)
 	source := getApplicationSource(app)