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ARM Template syntax and the native Bicep equivalent

In Bicep, we have tried to make some common syntax that in ARM templates is quite verbose and change it to a terser equivalent. This doc is a simple table to look at all of the changes in one place.

Scenario ARM Template Bicep
Author an expression [func()] func() (spec)
Concatenate strings together concat('John', ' ', parameters('lastName')) 'John ${lastName}' (spec)
Return the logical AND of multiple boolean values and(parameter('isMonday'), parameter('isNovember')) isMonday && isNovember (spec)
Get the resource ID of a resource declared in the template resourceId('microsoft.network/virtualNetworks') res.id
Get a property (resourceProperty) from a created resource (assumes resource named res has been declared in Bicep) reference(parameters('resourceName')).properties.resourceProperty res.properties.resourceProperty
Conditionally declare a property value if(parameters('isMonday'), 'valueIfTrue', 'valueIfFalse') isMonday ? 'valueIfTrue' : 'valueIfFalse' (spec)
Conditionally deploy a resource "condition": "[parameters('isMonday')]" resource foo '...' = if(isMonday) {...}
Separate a solution into multiple files Use linked templates Use modules
Set the target scope of the deployment to a subscription "$schema": "https://schema.management.azure.com/schemas/2018-05-01/subscriptionDeploymentTemplate.json#" targetScope = 'subscription' (spec)
Set a dependency between two resources "dependsOn": ["[resourceId('Microsoft.Storage/storageAccounts', 'parameters('storageAccountName'))]"] Either dependsOn not needed because of auto-dependency management or manually set dependsOn with dependsOn: [ stg ] (spec)
Iterate over an array or count Use the copy property Use for ... in ... loops (spec)
Get a reference to an existing resource reference(resourceId(...)).* each time you need a property Establish symbolic reference with resource foo '...' existing = {...} (spec)

Other notes on incorporating new syntax into best practices

  • Avoid the reference() and resourceId() functions unless absolutely necessary. Anytime the resource you are referencing is declared in the same Bicep project, you can pull the equivalent information from the resource identifier in Bicep (i.e. stg.id or stg.properties.primaryEndpoints.blob). This also creates an implicit dependency between resources, which means you can eliminate your usage of the dependsOn property. All of this results in cleaner, more maintainable code.
    • If the resource is not deployed in the Bicep file, you can still get a symbolic reference to the resource using the existing keyword
  • Use consistent casing for identifiers. When in doubt, use camel case (e.g. param myCamelCasedParameter string)
  • If you are going to add a description to a parameter, ensure the parameter is, in fact, descriptive. For example, if you have a location parameter, having a description of "the resource's location" is not particularly helpful and results in noisy code. Sometimes a // comment is more appropriate.