How to handle publishing event when message broker is out?

Question

I'm thinking how can I handle sending events when suddenly message broker go down. Please take a look at this code

using (var uow = uowProvider.Create())
{
    ...
    ...
    var policy = offer.Buy(customer);

    uow.Policies.Add(policy);

    // DB changes are saved here! but what would happen if...
    await uow.CommitChanges();

    // ...eventPublisher throw an exception?
    await eventPublisher.PublishMessage(PolicyCreated(policy));

    return true;        
}

IMHO if eventPublisher throw exception the event PolicyCreated won't be published. I don't know how to deal with this situation. The event must be published in system. I suppose that only good solution will be creating some kind of retry mechanism but I'm not sure...

Answer 1

For reliable system you need to save events locally. If your broker is down you have to retry and publish event.

There are many ways to achieve this but most common is outbox pattern. Just like your mail box your event/message stays locally and you keep retrying until it's sent and you mark the message published in your local DB.

you can read more about here Publish Events