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Choose a server engine

Katalyst runs on any of three Ktor server engines: Netty, Jetty, or CIO. You select one in the bootstrap by passing the engine object to engine(...).

katalyst-starter-web already bundles the Netty engine, so the default needs no extra dependency. To run on Jetty or CIO instead, add that engine's module — its version is managed by the BOM, so you omit the version — and the matching Ktor engine arrives transitively.

Select an engine

Bundled in katalyst-starter-web; no extra dependency. Just pass the engine object:

import io.github.darkryh.katalyst.ktor.engine.netty.NettyServer

fun main(args: Array<String>) = katalystApplication(args) {
    engine(NettyServer)
    // …
}

// build.gradle.kts — version comes from the Katalyst BOM
implementation("io.github.darkryh.katalyst:katalyst-ktor-engine-jetty")

import io.github.darkryh.katalyst.ktor.engine.jetty.JettyServer

fun main(args: Array<String>) = katalystApplication(args) {
    engine(JettyServer)
    // …
}

// build.gradle.kts — version comes from the Katalyst BOM
implementation("io.github.darkryh.katalyst:katalyst-ktor-engine-cio")

import io.github.darkryh.katalyst.ktor.engine.cio.CioServer

fun main(args: Array<String>) = katalystApplication(args) {
    engine(CioServer)
    // …
}

Each of NettyServer, JettyServer, and CioServer is an object implementing KatalystServerEngine, so swapping engines is a one-line change in the bootstrap (plus the engine module for non-default engines).

Which one

Engine Notes
Netty The common default for production HTTP services.
Jetty Servlet-based; useful in Jetty-aligned environments. Honors maxThreads / minThreads in the deployment config.
CIO Coroutine-based pure-Kotlin engine with no extra native dependencies.

Configure the engine

Engine-level settings (host, port, thread pools, timeouts, TLS) come from the ktor.deployment block when you enable server tuning:

features { enableServerTuning() }

The deployment keys, including which are engine-specific, are documented in the configuration reference.