provisionAfterExtension field for chaining multiple extensions…

[imvalient]

I am currently working with scale sets extensions and found out there is no way to define dependencies between scale-set extensions at ARM template level, through terraform.

Reading through the GO Azure SDK I found this feature exists, so I made an implementation that translates a terraform array of extensions dependencies to the AzureRM json based provisionAfterExtensions attribute.

Usage

resource "azurerm_virtual_machine_scale_set" "test_scale_set" {
    name = "scale-set-test-extension"
    ...
    
    extension {
        name = "first-extension"
        publisher = "Microsoft.Compute"
        ...
    }

    extension {
        name = "second-extension"
        publisher = "Microsoft.Compute"
        ...
        provision_after_extensions = ["first-extension"]
    }
}

This way the second extension will start only when the first one finishes, instead of running both at the same time.

As far as i know virtual machine extensions also do not implement this feature, you can define a terraform dependece using dependsOn, this could work at creation time but, once created, if the machine scales up, the dependency is lost as its not defined in the azure rm template, if this approach is alright we could add it to that resource as well.

[imvalient]

I ve been reviewing the GO SDK for virtual machines and did not find anything related to provisionAfterExtensions on it. I would appreciate if someone could review this for a final decision.

[katbyte]

Hi @imvalient,

Thank you for tis PR. Overall this looks good, however as you are updating the hash function a state migration is required to ensure that no diff is generated when users simply update to the new version.

You can find an example of a state migration function here

Additionally a test to ensure this property can be set would be ideal as well.

[imvalient]

The requested changes have been submitted.

[katbyte]

Thanks for the revisions @imvalient, this LGTM 👍

[ghost]

This has been released in version 1.28.0 of the provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading. As an example:

provider "azurerm" {
	version = "~> 1.28.0"
}
# ... other configuration ...

[ghost]

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