Application Gateway: fixing the permanent AGW tf update problem (fqdns)

[andrey-dubnik]

fixes: #2894

There is AGW issue when updating the configuration as TF populates the backend pool based on the computed values of fqdns and fqdn_list producing following state

"backend_address_pool.0.fqdn_list.#": "1", "backend_address_pool.0.fqdn_list.0": "wapazewtmlit-dnr-cm-tst1.azurewebsites.net", "backend_address_pool.0.fqdns.#": "1", "backend_address_pool.0.fqdns.0": "wapazewtmlit-dnr-cm-tst1.azurewebsites.net",

Where up on read values and populate both new and deprecated elements with identical values

`
flattenApplicationGatewayBackendAddressPools

        output := map[string]interface{}{
            "fqdns": fqdnList,
            "ip_addresses": ipAddressList,

            // TODO: deprecated - remove in 2.0
            "ip_address_list": ipAddressList,
            "fqdn_list": fqdnList,
        }
`

Because of this expandApplicationGatewayBackendAddressPools produces duplicates when AGW is updated because values only get duplicated by Read post GW creation.

PR only going into backendAddresses filling for the _list values when there are no fqdns and ip_addresses handled which is need to handle create (otherwise deprecated part could have been removed).

[katbyte]

Thanks for fixing this @adam-resdiary, LGTM provided tests pass 👍

[adam-resdiary]

@katbyte thanks for the thank you, although I think it's @adubnik who deserves the praise 😸

[Mobe1969]

Is there likely to be a new version of the azurerm provider module issues with this in? The module hasn't had a release since this was addressed.

[ghost]

This has been released in version 1.24.0 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 = "~> 1.24.0"
}
# ... other configuration ...

[ghost]

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