Amazon SNS message replay for FIFO topic subscribers

Amazon SNS replay lets topic subscribers retrieve archived messages from the topic data store and redeliver (or replay) them to a subscribed endpoint. Messages can be replayed as soon as the subscription is created. A replayed message has the same content, MessageId, and Timestamp as the original copy, and also contains the attribute Replayed, to help you identify that it's a replayed message. To only replay select messages, you can add a filter policy to your subscription. For more on filtering messages, see Filter replayed messages.

Create a message replay policy using the AWS Management Console

Use this option to create a new replay policy using the AWS Management Console.

To view and edit a message replay policy

You can perform the following actions from the Subscription details page:

Add a replay policy to the subscription using the API

To replay archived messages use the attribute ReplayPolicy. ReplayPolicy can be used with the Subscribe and SetSubscriptionAttributes API actions. This policy has the following values:

For example, to recover from a downstream failure and resend all messages for a two hour time period on October 1, 2023, use the SetSubscriptionAttributes API action to set a ReplayPolicy as follows:

{
  "PointType":"Timestamp", 
  "StartingPoint":"2023-10-01T10:00:00.000Z", 
  "EndingPoint":"2023-10-01T12:00:00.000Z"
}

To replay all messages sent to the topic as of October 1, 2023, and continue receiving all newly published messages to your topic, use the SetSubscriptionAttributes API action to set a ReplayPolicy on your subscription as follows:

{
  "PointType":"Timestamp",
  "StartingPoint":"2023-10-01T00:00:00.000Z"
}

To verify that a message has been replayed, the boolean attribute Replayed is added to each replayed message.

Add a replay policy to the subscription using the SDK

To use an AWS SDK, you must configure it with your credentials. For more information, see Shared config and credentials files in the AWS SDKs and Tools Reference Guide.

The following code example shows how to set the ReplayPolicy on a subscription to redeliver messages from the Amazon SNS FIFO topic's archive for a 2-hour time window on October 1st 2023.

// Specify the ARN of the Amazon SNS subscription to initiate the ReplayPolicy on.
String subscriptionArn =
    "arn:aws:sns:us-east-2:123456789012:MyArchiveTopic.fifo:1d2a3e9d-7f2f-447c-88ae-03f1c68294da";

// Set the ReplayPolicy to replay messages from the topic's archive 
// for a 2 hour time period on October 1st 2023 between 10am and 12pm UTC.
String replayPolicy =
    "{\"PointType\":\"Timestamp\",\"StartingPoint\":\"2023-10-01T10:00:00.000Z\",\"EndingPoint\":\"2023-10-01T12:00:00.000Z\"}";

// Set the ArchivePolicy for the Amazon SNS topic
SetSubscriptionAttributesRequest request = new SetSubscriptionAttributesRequest()
    .withSubscriptionArn(subscriptionArn)
    .withAttributeName("ReplayPolicy")
    .withAttributeValue(replayPolicy);
sns.setSubscriptionAttributes(request);

Understanding the EndingPoint

When you apply a ReplayPolicy to an Amazon SNS subscription, the EndingPoint value is optional. If no EndingPoint is provided, the replay will start from the specified StartingPoint and continue until it catches up to the current time, including processing any newly published messages. Once caught up, the subscription will function as a regular subscription, receiving new messages as they are published.

If an EndingPoint is specified, the service will replay messages from the StartingPoint up to the EndingPoint and then stop. This action effectively pauses the subscription. While the subscription is paused, newly published messages will not be delivered to the subscribed endpoint.

To resume message delivery, apply a new ReplayPolicy without providing an EndingPoint, and set the StartingPoint to the desired point in time from which to continue receiving messages. For example, to resume a subscription from where a prior replay finished, set the new StartingPoint to the previously provided EndingPoint.

Filter replayed messages

Amazon SNS message filtering let's you control the replayed messages that Amazon SNS replays to your subscriber endpoint. When message filtering and message archiving are both enabled, Amazon SNS first retrieves the message from the topic’s data store, then applies the message against the subscription’s FilterPolicy. The message is delivered to the subscribed endpoint when there is a match, otherwise message is filtered out. For more information, see Amazon SNS subscription filter policies.

Monitor message replay metrics using Amazon CloudWatch

You can monitor replay messages using Amazon CloudWatch using the following metrics. To be notified of anomalies in your workloads and help avoid impact, you can configure Amazon CloudWatch alarms on these metrics. For more details, see Logging and monitoring in Amazon SNS.