• Independent Consumption: Each message will be consumed independently by each consumer set up to handle it.
• Periodic Querying: Each instance of your app will periodically query the consumer_messages table for a batch of available messages to process.
• The query takes place at the frequency defined by ProcessorMaxDelay, if a full batch is returned it will delay by ProcessorMinDelay.
• Concurrency: Each app instance can run multiple parallel consumer processors defined by ConsumerMessageProcessorCount, unless using AsyncMonolith.Ef.
• Batching: Consumer messages will be read from the consumer_messages table in batches defined by ConsumerMessageBatchSize.
• Idempotency: Ensure your Consumers are idempotent, since they will be retried on failure.
• Timeout: Consumers timeout after the number of seconds defined by the ConsumerTimeout attribute or the DefaultConsumerTimeout if not set.

Example

[ConsumerTimeout(5)] // Consumer timeouts after 5 seconds
[ConsumerAttempts(1)] // Consumer messages moved to poisoned table after 1 failed attempt
public class DeleteUsersPosts : BaseConsumer<UserDeleted>
{
    private readonly ApplicationDbContext _dbContext;

    public DeleteUsersPosts(ApplicationDbContext dbContext)
    {
        _dbContext = dbContext;
    }

    public override Task Consume(UserDeleted message, CancellationToken cancellationToken)
    {
        ...
        await _dbContext.SaveChangesAsync(cancellationToken);
    }
}

Consumer Failures 💢

• Retry Logic: Messages will be retried up to MaxAttempts times (with a AttemptDelay seconds between attempts) until they are moved to the poisoned_messages table. Add the [ConsumerAttempts(1)] attribute to override this behavior.
• Manual Intervention: If a message is moved to the poisoned_messages table, it will need to be manually removed from the database or moved back to the consumer_messages table to be retried. Note that the poisoned message will only be retried a single time unless you set attempts back to 0.
• Monitoring: Periodically monitor the poisoned_messages table to ensure there are not too many failed messages.