How to let Lettuce notify application when connection is down?

Question

We are using Lettuce in our project. We have a requirement to monitor the status of connection.

I know Lettuce can re-connect Redis when the connection is down. But is there some way to notify application that the connection is down/up?

Thanks, Steven

Answer 1

Lettuce provides an event-model for connection events. You can subscribe to the EventBus and react to events published on the bus. There are multiple events, but for your case, you'd want to listen to connected and disconnected events:

• ConnectionActivatedEvent: The logical connection is activated and can be used to dispatch Redis commands (SSL handshake complete, PING before activating response received)
• ConnectionDeactivatedEvent: The logical connection is deactivated. The internal processing state is reset and the isOpen() flag is set to false.

Both events are fired after receiving Transport-related events such as ConnectedEvent respective DisconnectedEvent.

The following example illustrates how to consume these events:

RedisClient client = RedisClient.create()
EventBus eventBus = client.getresources().eventBus();

Disposable subscription = eventBus.get().subscribe(e -> {

    if (e instanceOf ConnectionActivatedEvent) {
        // …
    }
});

…
subscription.dispose();
client.shutdown();

Please note that events are dispatched asynchronously. Anything that happens in the event listener should be non-blocking (i.e. if you need to call blocking code such as further Redis interaction, please offload this task to a dedicated Thread).

Read more

• Lettuce Reference Documentation: Events