Is there any way to change a subset of variables in config depending on environment? What I'd like is something like

application.conf
    variable1: value1
    variable2: value2

application-dev.conf
    variable3: value3

And be able to run the application with both

application.conf

and

application-dev.conf

applied. Or possibly 1 config file but evaluate different configs depending on environment variables. When reading up on

HOCON

I couldn't find it it supports any kind of ternary operator or so.

You could just pass in another config in the command line https://ktor.io/servers/configuration.html#command-line

You can load Hocon by hand, too: if you pass in

-Dconfig.file=application.conf

it will load in

reference.conf

and then merge

application.conf

onto it And then you can instance your server like

val hoconConfig = ConfigFactory.load().resolve()
server = embeddedServer(YourEngine, applicationEngineEnvironment {
config = HoconApplicationConfig(hoconConfig)
}).start()