How does one Transform AppSettings in ASP.NET Core

Question

I was led to believe that appsettings.json and its environment counterparts (dev, staging, production) replaced Web.config transforms.

This works fine in a dev environment, where variables for those environments exist in the launchSettings.json

However, if I use the Publish feature, configuring the Publish to use the Staging build configuration which I created, no transform appears.

I've read elsewhere that you need to create Environment variables. Really! Is that what it has come to? We now have an armada of System Environment variables for Applications which may or may not (over time) be running on the IIS (or other) Web server on that box.

At the moment I am manually copying and pasting a "staging" appsettings.json after doing a publish. I already have to copy and paste a pre-prepared Web.config file into that folder as it is no longer available to configure in the IDE (yet curiously, still gets produced during a Publish operation).

Is there another way to have maintainable transforms for deployments which is something akin to the transforms of the config files of old?

Answer 1

This actually confuses a lot of people as the configurations in Visual Studio don't really do anything for an ASP.NET Core app. ASP.NET Core apps are intended to be compiled once for any environment. The actual "environment" it runs in is determined via config, namely the ASPNETCORE_ENVIRONMENT environment variable. In other words, whether you deploy as Debug/Staging/Release/Whatever in Visual Studio, it's the same app code. (The only time this is not the case is if you were to employ compiler directives in your code, like #if DEBUG ... #endif, for example. That's not very common and honestly not recommended anyways.)

I think you misunderstood about environment variables. You can still use JSON config and such in production. The only environment variable that needs to be set is the aforementioned ASPNETCORE_ENVIRONMENT.

Long and short, if you set ASPNETCORE_ENVIRONMENT to "Production", then your appsettings.Production.json will be loaded as you'd expect. There's no transformaton that occurs. Instead, the environment-specific config serves to extend and override other config.

Answer 2

I find this quite annoying too. I liked being able to change my solution configuration and test (locally) with production or staging config values.

Anyway, here is a low-ish friction option. There may be better out there.

1. Put all your production settings in appsettings.json. Worst case scenario is that something uses all the security levels of your production service, which is better than giving development access by accident. And it means you don't need an environment variable on your production boxes, so there's also nothing to accidentally delete
2. Create a appsettings.Development.json with your dev database connection string, etc. You only need the items that are different, and you don't have to transform them, they'll overwrite any matches in appsettings.json
3. lauchsettings.json should already be setup with a profiles > {name} > environmentVariables > ASPNETCORE_ENVIRONMENT with a value of Development. You can use this as your live test toggle. Comment out that line and you will use the Production settings.

If you want to add a Staging level, add yourself a new profile and appsettings.staging.json file. You will need to add the environment variable, but this is usually less of an issue and less of a risk than doing it on Production. I haven't thought of an easy way to use Staging and Development on the same box though