KTor site not reachable

Question

I want to make a simple http server using ktor. However, when I enter the site (127.0.0.1:8080 or 0.0.0.0:8080), it just isn't there. It doesn't print and doesn't respond.
However if I use NanoHttpd instead of ktor, everything works fine. What is my issue?

import io.ktor.application.call
import io.ktor.http.ContentType
import io.ktor.response.respondText
import io.ktor.routing.get
import io.ktor.routing.routing
import io.ktor.server.engine.embeddedServer
import io.ktor.server.netty.Netty


fun main() {
    val server = embeddedServer(Netty, port = 8080) {
        routing {
            get("/") {
                println("TEST")
                call.respondText("Hello World!", ContentType.Text.Plain)
            }
        }
    }
    server.start(wait = true)
}

The output is just:

[main] INFO ktor.application - No ktor.deployment.watch patterns specified, automatic reload is not active
[main] INFO ktor.application - Responding at http://0.0.0.0:8080

Answer 1

It could be one of the following things:

1. The application code
2. The run configuration

I am leaning towards there being a problem with the run configuration rather than the application code.

Application code

Even though I think your issue is with the run configuration, in case that it isn't, I'm providing sample code here.

When I use the IntelliJ Ktor plugin, the Ktor app is bootstrapped as follows:

Application.kt

package com.example

import io.ktor.application.*
import io.ktor.http.*
import io.ktor.response.*
import io.ktor.routing.*

fun main(args: Array<String>): Unit = io.ktor.server.netty.EngineMain.main(args)

@kotlin.jvm.JvmOverloads
@Suppress("unused") // Referenced in application.conf
fun Application.module(testing: Boolean = false) {
    routing {
        get("/") {
            call.respondText("Hello, world!", ContentType.Text.Plain)
        }
    }
}

application.conf

ktor {
    deployment {
        port = 8080
        port = ${?PORT}
    }
    application {
        modules = [ com.example.ApplicationKt.module ]
    }
}

I've provided an example Ktor code base here: https://gitlab.com/tinacious/ktor-example

Run configuration

It could be your run configuration in IntelliJ. It needs to be set up as a Kotlin script (and not an Application). When it's set up as an Application, I get the same error you do. Here is how to set up the run configuration I have, allowing me to run the server in IntelliJ:

1. Add a configuration
2. Choose Kotlin script from the Templates section. Do not choose Application.
3. Near the bottom where it says "Use classpath of module" choose your application.main.
4. Near the top where it says "Main class" you should be able to choose your main application. I found this only showed up after I chose the classpath of the module.

Here are the relevant sections in the configuration:

Here is what I describe in step 4, i.e. I can choose my main class after the class path is added:

The run symbol should be a Kotlin logo:

I would recommend installing the IntelliJ Ktor plugin for bootstrapping your project. It uses Gradle and bootstraps everything so when you run ./gradlew run, you are running it properly and can access it without the manual build configuration step.