Hello again, :wave::skin-tone-4: I was doing a bit of research regarding the best approach to Grace...

# ktor

[Helio]

Hello again, 👋🏽

I was doing a bit of research regarding the best approach to Gracefully Shutdown a Ktor server (Netty Engine - more specifically). Looking through the documentation, I thought that the recommended way would be through Application Monitoring Events (e.g getting SIGTERM signals). However, during my tests, I noticed that onStopping, onPrepareStop and onStopped ApplicationEvents are not triggered for Netty Engine? Is that expected? If so, do you have any suggestion to properly handle those Graceful Shutdowns?

Thanks once again for your help.

[Aleksei Tirman [JB]]

I cannot reproduce your problem:

val server = embeddedServer(Netty, port = 3333) {
   environment.monitor.subscribe(ApplicationStopping) {
       println("Stopping")
   }

    environment.monitor.subscribe(ApplicationStopped) {
        println("Stopped")
    }

    environment.monitor.subscribe(ApplicationStopPreparing) {
        println("Preparing")
    }
}

server.start(wait = false)
server.stop()

[Helio]

Did you try terminating the application with kill -15 PID? I'm afraid it won't print

[Helio]

This is how I was testing.

fun main() {
    startKoin { modules(httpClientModule, serviceModule, useCaseModule, redisModule) }
    embeddedServer(Netty, port = 8080, module = Application::module).start(wait = true)
}

fun Application.module() {
    environment.monitor.subscribe(ApplicationStarting) { print("Starting") }
    environment.monitor.subscribe(ApplicationStarted) { print("Started") }
    environment.monitor.subscribe(ApplicationStopping) { print("Stopping") }
    environment.monitor.subscribe(ApplicationStopped)  { print("Stopped") }
    environment.monitor.subscribe(ApplicationStopPreparing)  { print("Preparing") }
}

[Helio]

Even the SIGINT signal sent by IntelliJ is not caught.

[Andreas Scheja]

I believe you will have to add a shutdown hook in which you stop the server

val server = embeddedServer(Netty, port = 8080) {
  ...
}
Runtime.getRuntime().addShutdownHook(
    thread(start = false) {
        server.stop()
    }
)
server.start(wait = true)

[Aleksei Tirman [JB]]

Or you can use the addShutdownHook method:

server.addShutdownHook {
    server.stop()
}

[Helio]

Ohhh, I see! This is what I was missing I guess.
Thanks for your help guys. 😃