Spring MVC shutdown hook

Question

I'm using Curator service discovery with Spring MVC rest controllers where each controller registers itself with ZooKeeper in @PostConstruct and de-registers itself in @PreDestroy.

The problem I'm having is that by the time the @PreDestroy method is called, the controller is already no longer servicing requests. I need to de-register the controller before the controller stops servicing requests to avoid throwing exceptions for the small number of requests that occur between the controller stopping and de-registration.

I've tried the spring ApplicationListener interface, SmartLifecycle, and ServletContextListener and in all shutdown/close related hooks, the controller has already stopped servicing requests.

I need a shutdown hook where I can deregister before the controller stops servicing requests, and I'm not sure one is available.

Answer 1

I don't believe such hook exists in Spring.

However, you could have a special controller, mapped to a specific reserved url, i.e. ending in /activity/suspend-traffic. You might want to have some sort of basic security for that, maybe an application specific token, i.e. /activity/suspend-traffic/{token}.

When this special controller receives the correct token, it deregisters all application controllers from ZK.

This way you wouldn't loose any request. Then, when the application is no longer receiving traffic, you could safely shutdown the server. After sending /activity/suspend-traffic/{token}, you could wait a fixed amount of time before shuting down, so that the server finishes processing the requests it has received after the suspend command.

Or you might implement a more sophisticated mechanism, i.e. via a filter or mvc interceptor that counts how many requests are "inside" the application. You could have another mapping in that special controller, i.e. /activity/request-count that returns the actual number of requests being processed. When this request returns 0, it would be safe to shutdown the server.