Hey has anyone implemented graceful shutdowns with Ktor I m kotlinlang #ktor

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.

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.

Oh, we're using the Netty engine

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

11/19/2019, 3:13 AM

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

11/19/2019, 7:11 PM

yeah we use

Runtime.getRuntime().addShutdownHook

napperley

11/19/2019, 11:30 PM

Is that the Runtime class from the JDK?

Ran Magen

11/19/2019, 11:41 PM

yes

we have a globally available util function:

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

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