Ktor - Create Multiple Subdomains Programatically

Issue

Okay so this may sound like a stupid question, but I really need to know, is there a way to create multiple domains programatically with Ktor. For example, let's say that I have a domain: example.com

Now I need the logic on my backend server to create a new subdomain for each user that register on my website. For example, when John register, I want to immediately be able to create a new subdomain: john.example.com . Now I'm not sure what and how this can be achieved, that's why I'm asking here for some directions?

And if that's too complex, then is there a way to create multiple endpoints dynamically from the code, after each and every user registration on my website, like: example.com/John ?

Is there any good resource that I can read about that?

Solution

On the Ktor side, you can add routes dynamically after the server startup and use the host route builder to match the requested host. Additionally, you need to add DNS entries programmatically as @Stephen Jennings said. Here's an example where after 5 seconds the route for the host john.example.com is added. You can test it locally with the entry 127.0.0.1 john.example.com in the /etc/hosts file.

import io.ktor.application.*
import io.ktor.http.*
import io.ktor.response.*
import io.ktor.routing.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
import kotlinx.coroutines.*

fun main() {
    val server = embeddedServer(Netty, port = 4444) {
        routing {
            get("/example") {
                call.respondText { "example" }
            }
        }
    }

    server.start(wait = false)

    CoroutineScope(Dispatchers.IO).launch {
        delay(5000)
        val routing = server.application.feature(Routing)
        routing.addRoutesForHost("john.example.com")
    }
}

fun Route.addRoutesForHost(host: String) {
    host(host) {
        get("/hello") {
            call.respondText { "Hello ${call.request.headers[HttpHeaders.Host]}" }
        }
    }
}

Answered By - Aleksei Tirman