Best way to include an external definition into existing bicep file

[mgreisen]

We have an open-source project where we want to use bicep to deploy a VM scale set. However different users of the project will want different VM Extensions deployed.

These would be the extensions defined under virtualMachineProfile -> extensionProfile -> extensions.
There may be 0 or more extensions that a particular instance of the deployment would want to use.

Since there is no #include functionality, what's the suggestion on the best way to solve this kind of problem?

[brwilkinson]

I have been using this for my VMSS extensions for some time now.

https://docs.microsoft.com/en-us/azure/templates/microsoft.compute/virtualmachinescalesets?tabs=bicep#virtualmachinescalesetextension

The disadvantage of using that approach is that the extensionprofile/extensions does not support conditions.

https://github.com/brwilkinson/AzureDeploymentFramework/blob/main/ADF/bicep/VMSS-VM.bicep#L302

However, looking at the docs, it does look as if you can use the following, which is identical to Virtual Machines. I did some basic testing and it does appear to work fine.

https://docs.microsoft.com/en-us/azure/templates/microsoft.compute/virtualmachinescalesets/extensions?tabs=bicep

So based on that, I can offer you a solution, although for my answer I will model this on Virtual Machines, not VMSS, however now assuming they will function identically (I will do more research on this and likely move my VMSS template to use this method as well).

So.... here is a Virtual Machine template, with a list of individual extensions

https://github.com/brwilkinson/AzureDeploymentFramework/blob/main/ADF/bicep/VM-VM.bicep#L703

resource AppServerMonitoringAgent 'Microsoft.Compute/virtualMachines/extensions@2020-12-01' = if (VM.match && bool(VM.Extensions.MonitoringAgent)) {
  name: 'MonitoringAgent'
  parent: virtualMachine
  location: resourceGroup().location

here is a parameter file that gets passed into the template.

https://github.com/brwilkinson/AzureDeploymentFramework/blob/main/ADF/tenants/AOA/ACU1.T5.parameters.json#L80

    "Extensions": {
      "value": {
        "MonitoringAgent": 1,
        "IaaSDiagnostics": 1,
        "DependencyAgent": 1,
        "AzureMonitorAgent": 1,
        "GuestHealthAgent": 1,
        "VMInsights": 1,
        ...

Based on the setting in the parameter file set to a 1 or 0, or if you prefer a true or a false, the extension condition will either include or exclude the extension.

e.g. if (bool(Extensions.MonitoringAgent))

This is basically a feature flag model/pattern ...

[brwilkinson]

I did a bit more testing on this... still seems to work, however I did need to add explicit dependson between the different extensions to avoid errors relating to "The request failed due to conflict with a concurrent request".

So keep that in mind. I still have more testing to do... I would also like to find some official docs on this different approach for managing the extensions.

https://github.com/brwilkinson/AzureDeploymentFramework/blob/main/ADF/bicep/VMSS-VM.bicep#L622

[brwilkinson]

Based on the title of the discussion, I figured that I would also offer an alternate perspective... for an answer.

You can currently load external data from a file using loadtextcontext('file.json'), however there is currently no way to make that value for the file path a variable or a parameter, so it doesn't suit the needs of a user passing in alternate configurations.

https://docs.microsoft.com/en-us/azure/azure-resource-manager/bicep/bicep-functions-files#loadtextcontent

There is a request here to provide such functionality, however it is not currently supported.
#3816

[brwilkinson]

Also adding the link to the configuration set pattern, however this is unlikely to suit, unless there are pre-determined sets of configurations that the end user would be able to select (as a lookup).

https://docs.microsoft.com/en-us/azure/azure-resource-manager/bicep/patterns-configuration-set