Version 4 (V4) of the AWS SDK for .NET has been released\$1

For information about breaking changes and migrating your applications, see the [migration topic](https://docs.aws.amazon.com/sdk-for-net/v4/developer-guide/net-dg-v4.html).

 [https://docs.aws.amazon.com/sdk-for-net/v4/developer-guide/net-dg-v4.html](https://docs.aws.amazon.com/sdk-for-net/v4/developer-guide/net-dg-v4.html)

# Using FIFO with the AWS Message Processing Framework for .NET
<a name="msg-proc-fw-fifo"></a>

For use cases where message ordering and message deduplication are critical, the AWS Message Processing Framework for .NET supports first-in-first-out (FIFO) [Amazon SQS queues](https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-fifo-queues.html) and [Amazon SNS topics](https://docs.aws.amazon.com/sns/latest/dg/sns-fifo-topics.html).

## Publishing
<a name="mpf-fifo-publish"></a>

When publishing messages to a FIFO queue or topic, you must set the message group ID, which specifies the group that the message belongs to. Messages within a group are processed in order. You can set this on the SQS-specific and SNS-specific message publishers.

```
await _sqsPublisher.PublishAsync(message, new SQSOptions
{
    MessageDeduplicationId = <message-deduplication-id>,
    MessageGroupId = <message-group-id>
});
```

## Subscribing
<a name="mpf-fifo-subscribe"></a>

When handling messages from a FIFO queue, the framework handles messages within a given message group in the order in which they were received for each `ReceiveMessages` call. The framework enters this mode of operation automatically when configured with a queue ending in `.fifo`.

```
await Host.CreateDefaultBuilder(args)
    .ConfigureServices(services =>
    {
        // Register the AWS Message Processing Framework for .NET.
        services.AddAWSMessageBus(builder =>
        {
            // Because this is a FIFO queue, the framework automatically handles these messages in order.
            builder.AddSQSPoller("https://sqs.us-west-2.amazonaws.com/012345678910/MPF.fifo");
            builder.AddMessageHandler<OrderMessageHandler, OrderMessage>();
        });
    })
    .Build()
    .RunAsync();
```