Hey, has anyone implemented graceful shutdowns with Ktor? I'm looking for a way to "drain" ongoing r...

# ktor

[Ran Magen]

Hey, has anyone implemented graceful shutdowns with Ktor? I'm looking for a way to "drain" ongoing requests before the process shuts down after being sent a SIGTERM.
I can implement this myself, though if there's already a commonly used feature, I'd opt to not re-invent the wheel.

My general idea is to set some boolean like stopRequested when getting a SIGTERM and maintain another var active: Int with the current number of active requests similar to https://github.com/ktorio/ktor/blob/master/ktor-features/ktor-metrics/jvm/src/io/ktor/metrics/dropwizard/DropwizardMetrics.kt#L22
so when that number hits 0 and stopRequested is true, only then finish the process.

[Ran Magen]

The use case is that when we deploy our service to our kubernetes environment, pods of the old version get sent a SIGTERM and have some graceful shutdown time. Right now they die while requests are in flight and we see a dip in success rate.

[Ran Magen]

Oh, we're using the Netty engine

[Ran Magen]

hmm it seems that parameters on server.stop should suffice? we have them set to

server.stop(gracePeriod = 10, timeout = 10, timeUnit = SECONDS)

Hm I'll go back to this. Maybe this is more of a k8s problem sending requests to the pod after the SIGTERM or maybe we have some very slow requests.

[napperley]

If there was a Kotlin Native version of Ktor Server for Linux then one would expect there is functionality to catch the signals. Highly unlikely that the Kotlin JVM version of Ktor Server would allow catching of signals.

[Ran Magen]

yeah we use Runtime.getRuntime().addShutdownHook

[napperley]

Is that the Runtime class from the JDK?

[Ran Magen]

yes

[Ran Magen]

we have a globally available util function:

fun onShutdown(action: () -> Unit) =
	Runtime.getRuntime().addShutdownHook(Thread(action))