Should this.existingResource() work in the Microsoft.Web/sites/config resource for appsettings?

[ronaldbosma]

I saw the blog post How to use the this namespace in Bicep to check resources from Gijs Reijn and thought it might be useful for the following scenario: I've had several projects with a separation in platform and application teams. The platform team is responsible for deploying the infrastructure, including App Services, while the application team deploys the application code. In such scenarios, the platform team often configures default app settings required for the App Service, and the application team adds application specific app settings.

To prevent deployments from removing app settings from the other team, I'm currently using a module that allows existing app settings to be merged with new app settings. Both the platform and application team need to use it to not overwrite each others app settings.

I was hoping that this.existingResource() might replace this and I could do something like this:

var additionalAppSettings object = {
  APP_SPECIFIC_SETTING_1: 'SomeValue'
  APP_SPECIFIC_SETTING_2: 'AnotherValue'
}
resource siteAppSettings 'Microsoft.Web/sites/config@2024-04-01' = {
  parent: site
  name: 'appsettings'
  properties: union(additionalAppSettings , this.existingResource().?properties)
}

However, this.existingResource().?properties seems to always be an empty object in this case.

I've worked out a scenario to try it out (note: it's on the this-existing-resource branch):

• This site.bicep will deploy a function app with some default app settings as show in this image.

  

• This additional-app-settings.bicep should add some more app settings. Here's the snippet I'm using:

  resource siteAppSettings 'Microsoft.Web/sites/config@2024-04-01' = {
    parent: site
    name: 'appsettings'
    properties: {
      THIS_EXISTS: this.exists()
      THIS_EXISTING_RESOURCE_PROPERTIES: string(this.existingResource().?properties)
      ANOTHER_SETTING: 'AnotherValue'
    }
  }

  The THIS_EXISTS app setting will get a value of true, but the THIS_EXISTING_RESOURCE_PROPERTIES has a value of {} instead of an object with the existing app settings. See the image below.

  

You can execute the scenario with the deploy.ps1 script by running the following command where <your-resource-group> is the name of your resource group:

. .\deploy.ps1 -ResourceGroupName "<your-resource-group>"

Note that you curently need to install the nightly bicep cli build for this feature to work.

[tsmallig33]

Created issue: Azure/bicep-types-az#2639. For Microsoft.Web/sites/config appsettings, empty properties are returned for existing resources.

[slavizh]

@tsmallig33 They are empty because the app settings contain sensitive data thus they require the usage of list function in order to be pulled. If this.existingResource() syntax does not support list() to be used somehow it is something that the Bicep team should look at if it can be supported.