Dynamically Build Dependencies

[joehubbert]

As a Bicep Developer
I want to be able dynamically build dependsOn objects natively in Bicep based on conditions
So that I am able to fully support modulised deployments so I don't have to deploy the whole solution/main.bicep every time

Describe the solution you'd like
My example main.bicep has modules for:

• appConfigurationStore
• containerAppManagedEnvironment
• keyVault
• postgresqlFlexibleServer
• storageAccount
• virtualNetwork

Each of these modules will deploy if a corresponding bool parameter is true e.g. deployAppConfigurationStore.
Some of these conditions are simple and are supported in bicep today.

In the case of containerAppManagedEnvironment I can do this as there are no other dependencies.

  dependsOn: deployVirtualNetwork ? [
    virtualNetwork
  ] : []

In the cases of appConfigurationStore and postgresqlFlexibleServer I have dependencies on virtualNetwork and keyVault. However, that dependency is only valid for a "full deployment". There is a use case where I only want to deploy specific components in the solution such and which components I pick changes each time.

I have asked ChatGPT this question and it suggested this solution:

var appConfigurationStoreConditionalDependsOn = [
  deployVirtualNetwork ? virtualNetwork : null
  deployKeyVault ? keyVault : null
]

var appConfigurationStoreConditionalDependsOnFiltered = [for dependency in appConfigurationStoreConditionalDependsOn: dependency != null ? dependency : []]

module appConfigurationStore 'appConfigurationStore.bicep' = if (deployAppConfigurationStore) {
  dependsOn: appConfigurationStoreConditionalDependsOnFiltered

This does not seem to be supported:
[for dependency in appConfigurationStoreConditionalDependsOn - 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 ("appConfigurationStoreConditionalDependsOn" -> "virtualNetwork"). Properties of virtualNetwork which can be calculated at the start include "name".

dependency != null ? dependency : []] - The property "dependsOn" expected a value of type "module[] | (resource | module) | resource[]" but the provided value is of type " | module | module | null".

It would be awesome to solve this, there are other pipelines I have that have even more dependencies

[jeskew]

You should be able to include conditionally deployed resources in another resource's dependsOn list without an issue -- the backend should filter any non-deployed resources from the list. Did you run into any issues that prompted this approach?

[joehubbert]

That approach doesn't work for me because I'm using unique deployment names e.g. keyVault-2025-03-11-10-00 and it will search for a deployment that doesn't exist in that scenario

[jeskew]

That shouldn't be a problem. The following template deploys without issue, even though the anotherOne module has a dependency on the empty module, which won't be deployed:

param moduleName string = newGuid()

module empty 'empty.bicep' = if (false) {
  name: moduleName
}

module anotherOne 'empty.bicep' = {
  name: uniqueString(moduleName)
  dependsOn: [
    empty
  ]
}

The deployments engine will look at what's in dependsOn, verify that everything in the list corresponds to a resource in the template, and then ignore any dependency on a resource with a false condition. There's a bit more detail on the docs page on the expected behavior.