I have a specific requirement for ARM templates and Azure API Management, so this question is different than other conditional ARM deployment questions.
Some background: My APIM instance is deployed using ARM templates, however custom domains need to be setup but cannot be part of it. This is because my customer stores their certificates in a different system. This means the custom domains are setup separately (manually) for the APIM instance, right after the instance was created by the ARM template. The ARM template also applies the global policy and creates the products. I use a linked template setup.
The issue arises when we want to update something on the APIM instance, like extending the global policy or adding a product. Then the ARM template will also update the instance, but should leave the custom domain section untouched. According to the documentation, using 'incremental' mode leaves resources not in the ARM template untouched. So I thought to solve it by just leaving out the 'hostnameConfigurations' section in the ARM template. However it seems the ARM template doesn't ignore it, but interprets it as empty and effectively removing the custom domains from the APIM instance!
This doesn't seem like normal behavior, but I have to live with it. To solve this I have a couple of options. One of them is extracting the global policies and products from the generic APIM ARM template, so I can skip the APIM instance part when updating. This would mean I have to run multiple separate ARM templates on creating the resources.
The solution I'd like to go for, is to conditionally deploy the ARM template creating the APIM instance, to only creating. I want to skip this linked template when the resource already exists. I though I could do this by getting a reference to the APIM instance, but according to the documentation "The reference function derives its value from a runtime state, and therefore can't be used in the variables section.".
Question: Is it possible to conditionally deploy a linked ARM template, based on the fact whether a resource already exists or not?
