When we deploy a Custom template in Azure then few parameters like Resource Group and Region are automatically popped up in the Azure portal (see the attached screenshot). I want to know that how can we customize or restrict the list of Region using ARM templates?
ARM Template Deployment Screenshot
Edit
New parameter Region is added rather than re-using the existing one
The first "region" dropdown is for the resourceGroup's location - it's required when creating a new one, disabled when using an existing one. For a custom template, you cannot customize or remove that control unless you provide your own ui definition file.
That said, there's also nothing that requires you to use the value from that control in your deployment. If you want to use that value you'd reference it using resourceGroup().location in your template. That would allow you to remove the "duplicate" but also requires that the resources are deployed to the same region as the resourceGroup.
For your own "region" control, you can use the allowedValues property on the parameter in the template and that will restrict the items in the list to what you provide - that's the link that Jim provided in the comment above.
If you supply your own ui definition file there are more things you can do to restrict the list, but requires you to write a bit more code. This would be the starting point:
The docs talk about managedApplications, but the ui is a generic construct that you can use for template deployments, here's a generic example:
https://github.com/Azure/azure-quickstart-templates/tree/master/100-marketplace-sample
[edits post comment]
If you want to leverage the "built-in" region control you can customize the list of locations that appear there by setting the config in the createUiDefintion.json file. More on that here:
