A module referred to twice from other modules

[msansemenov]

I've a module declaring a storage account, "ModStor"

This module is referred to in VirualMachineScaleSets, "VMSS"

It is also referred to in Cluster module, "Cluster", which in turn is also referred to in "VMSS"

The overall chain of dependencies is like:

VMSS -------------------- ModStor
    \----- Cluster -----/

This produces several deployment templates within the main ARM template when compiled, and ModStor deployment is then rendered twice with its respective StorageAccount resource deployment in it.

All the modules are declared to be targetScope = 'resourceGroup'

How to avoid spawning several deployments for the same resource even if it's referred to several times across the dependency chains within the modules references?

[ahelland]

I try to keep my modules at the resource group scope but collecting them in a pattern on subscription scope. (Or by "Levels" depending on the intent.)

targetscope = 'subscription'

module storage 'storage.bicep' = {
 ...
}

module vmss 'vmss.bicep' = {
 properties:
   storageAccount: storage.id
}

module cluster 'cluster.bicep" = {
  properties:
    storageAccount: storage.id
    vmss: vmss.id
}

Depending on how the individual module uses the storage account it could be that just referencing the id directly works, or you might need to do an import with the 'existing' keyword.

Obviously the above is only pseudo-coding it so if it works in your specific use case I can't tell - that's just how I try to structure similar use cases.

[msansemenov]

According to the docs existing is only allowed for resource declarations, not module. This brings in another issue then:

Suppose I include all the modules separately into the main Bicep module and only refer to their resources across those modules as resource existing. Then, if at some point we upgrade the infrastructure to not use cluster and vmss anymore, we have to manually track down the unused storage account and comment/remove it as well. Otherwise, Bicep won't disable it automatically.

By importing modules within modules I've tried to achieve automatic dependency resources declaration, so I don't need to manually disable those resources, which don't get required within some particular deployment according to some parameter flags. For example, module if provides with such a possibility. And yes, our implementations introduce that diamond problem which I don't know how to manage with Bicep language for it to not declare the same resource more than once during the template compilation.