Has anyone tried the instant start JVM feature <CRaC> with ktor yet?

# ktor

[spierce7]

Has anyone tried the instant start JVM feature CRaC with ktor yet?

[Luca]

Hi @spierce7 do you try with CRaC on ktor?

[spierce7]

I have not. I am reasonably confident it would work though.

[Luca]

searching for examples I didn't find any, only with spring

[spierce7]

It should be the same process for both

[Luca]

But seems the spring guys did something https://docs.spring.io/spring-framework/reference/integration/checkpoint-restore.html ... some kind of shortcut with org.crac.resource interface implementation on beans

[spierce7]

You mean

When the -Dspring.context.checkpoint=onRefresh JVM system property is set, a checkpoint is created automatically at startup during the LifecycleProcessor.onRefresh phase. After this phase has completed, all non-lazy initialized singletons have been instantiated, and InitializingBean#afterPropertiesSet callbacks have been invoked; but the lifecycle has not started, and the ContextRefreshedEvent has not yet been published.

[spierce7]

This looks like all they are doing

[spierce7]

https://github.com/spring-projects/spring-framework/blob/a985c0bb35403a3e6722f6efc[…]/springframework/context/support/DefaultLifecycleProcessor.java

[spierce7]

public static final String CHECKPOINT_PROPERTY_NAME = "spring.context.checkpoint";
private static final boolean checkpointOnRefresh =
			ON_REFRESH_VALUE.equalsIgnoreCase(SpringProperties.getProperty(CHECKPOINT_PROPERTY_NAME));	

	if (checkpointOnRefresh) {
		new CracDelegate().checkpointRestore();
	}

[spierce7]

Take a look at what they are doing. This seems super easy to replicate.

[Luca]

Yes sounds easy to replicate, the doubt I keep is about the server itself, there is a specific topic talking about must be 0 connection in activity.

[spierce7]

that seems reasonable

[spierce7]

connections wouldn't be able to restore

[spierce7]

but that's also easy to control I think

[Luca]

Shutdown the server is easy yes, but you need to shutdown only the server connections and keep the server/JVM ON, so you can resume again in this state. This is far I understood 😄

[spierce7]

I mean, your goal is to start up the app, create a restore checkpoint, and then kill the process, or, I'm not sure exactly how it works

[Luca]

Yes exactly, but what I read told this part about stop the active connections, this is a must