Hi all, I am having an issue with ktor cold start ...

# ktor

[Moses Mugisha]

Hi all, I am having an issue with ktor cold start for each request endpoint after deployment. What is the normal workaround or is this a misconfiguration on my end?

[mp]

Can you be more specific?

[Moses Mugisha]

So, I have a ktor app installed in kubernetes. After each deploy, the endpoint latency is terrible for the first request, but then gets better for sub sequent requests. Is there a way around this?

[Moses Mugisha]

also, its not a serverless model (like lambda) in k8s. I cant figure out why that would be happening

[mp]

perhaps the way you are setting up your various components is deferring work until it is first used

[mp]

it is certainly not an intrinsic problem with ktor

[mp]

e.g. if you are using Guice, make sure you're using Stage.PRODUCTION to eagerly evaluate all bindings, etc.

[mp]

One of my production ktor services is about 35kloc, has various external services to connect to (e.g. a sql database, redis, etc), and is fully up and running in about 1200ms, to give you an idea of what is reasonable. No issues on the first request.

[Moses Mugisha]

I am using Jackson Convertor. I am not sure how to make it eager

[Moses Mugisha]

install(ContentNegotiation) {
    register(ContentType.Application.Json, JacksonConverter())
}

[Moses Mugisha]

Are you using the default engine configs?

[Jeff]

Could you be making database migrations when the app starts? I was also experiencing the same problem.

[Moses Mugisha]

Not migrations per se, but I think I probably need to warm up the database connection pool

[mp]

See https://bitbucket.org/marshallpierce/ktor-demo/src/master/. From the start of main to fully initialized ktor is about 400ms.

[mp]

Note how it's using CompletableFuture.supplyAsync to load things like jackson on another thread (specifically, in the common fork join pool)

[Moses Mugisha]

Awesome! thanks. I am going to experiment with it

[Iftekhar Khan]

@Moses Mugisha - Can you please share what changes you did for fixing cold start issue, and did it really worked ?