App Insights Connection String reference, give ERROR BCP178, with for loop - azure

Question

I have a bicep that creates apps in for loop.
var App = {
(...)
}
module app 'app:latest' = [for i in range(0, length(App.appServices)): {
name: 'app${i}'
params: {
(...)
}
}]
I want to connect it with app insights.
I found I could use reference to resolve APPLICATIONINSIGHTS_CONNECTION_STRING:
siteConfig: {
linuxFxVersion: 'NODE|14-lts'
appSettings: [
{
name: 'APPLICATIONINSIGHTS_CONNECTION_STRING'
value: reference(resourceId(resourceGroup().name,'Microsoft.insights/components/', 'app1'), '2020-02-02').ConnectionString
}
And unfortunately this throw error:
Error BCP178: This expression is being used in the for-expression, which requires a value that can be calculated at the start of the deployment. You are referencing a variable which cannot be calculated at the start ("App" -> "applicationinsights_connection_string" -> "reference").
INFO: Command ran in 17.855 seconds (init: 0.252, invoke: 17.602)
How do I make it work? How do I force bicep to resolve it first?
Is there another way to link apps created with for loop with application insights?
P.S
code above works fine without for loop for a single app.

Answer 1

Error BCP178: This expression is being used in the for-expression, which requires a value that can be calculated at the start of the deployment.
This error means that referencing value must be given before the loop begins. So, build an array of connection strings outside of the loop and then reference that array within the loop.
create an array of connection strings by using a for loop outside of the module declaration. We then reference this array inside the loop that creates the app modules and assign the appropriate connection string to the params. appInsightsConnectionString property.
var appInsightsConnections = [ for i in range(0, length(app1.appServices)): ```
reference(resourceId(resourceGroup().name,'Microsoft.insights/components/', 'app1'), '2020-02-02').ConnectionString]
Add this in your bicep code:
params: {
(...)
appInsightsConnectionString: appInsightsConnections[i]
}
I made the above changes and ran a sample template taken from MSDoc and was able to deploy it successfully.
Refer this template to connect an app service with application insights.