Application-Autoreload.md

During development it is important to have fast feedback loop cycle. Often, restarting server would take quite some time, so Ktor provides basic auto-reload facility that reloads just an Application. To enable this feature, add autoreload and watch keys to ktor.deployment configuration.

autoreload – Feature is enabled when this value is true watch - Array of module names that should be automatically reloaded.

ktor {
    deployment {
        port = 8080
        autoreload = true
        watch = [ module1, module2 ]
    }
    
    …
}

For now watch keys are just strings that are matched with contains against classpath entries of the loaded application, such as a jar name or a project directory name. These classes are then loaded with special ClassLoader that is recycled when change is detected.

Note: ktor-core classes are specifically excluded from auto-reloading, so if you are working on something in ktor itself, don't expect it to autoreload. It can't work because core classes are loaded before auto-reload machinery kicks in. The exclusion can potentially be smaller, but it's hard to analyse all the transitive closure of types loaded during startup.