Message replay for FIFO topic subscribers - Amazon Simple Notification Service
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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 Amazon Web Services Management Console

Use this option to create a new replay policy using the Amazon Web Services Management Console.

  1. Sign in to the Amazon SNS console.

  2. Choose a topic subscription or create a new one. To learn more about creating subscriptions, see Subscribing to an Amazon SNS topic.

  3. To initiate the message replay, go to the Replay drop-down and choose Start replay.

  4. From the Replay timeframe modal, make the following selections:

    1. Choose replay start date and time – Choose the date (YYYY/MM/DD format) and time (24-hour hh:mm:ss format) from which you want to start replaying archived messages. The start time should be later than the beginning of the approximated archive time.

    2. (Optional) Choose replay end date and time – Choose the date (YYYY/MM/DD format) and time (24-hour hh:mm:ss format) when you want to stop replaying archived messages.

    3. Choose Start replay.

  5. (Optional) To stop a message replay, go to the Subscription details page and choose Stop replay from the Replay drop-down.

  6. (Optional) To monitor message replay metrics from within this workflow using CloudWatch, see Monitor message replay metrics using Amazon CloudWatch.

To view and edit a message replay policy

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

  • To view the message replay status, the Replay status field displays the following values:

    • Completed – The replay has successfully redelivered all messages, and is now delivering newly published messages.

    • In progress – The replay is currently replaying the selected messages.

    • Failed – The replay was unable to complete.

    • Pending – The default state while the replay initiates.

  • (Optional) To modify a message replay policy, go to the Subscription details page and choose Start replay from the Replay drop-down. Starting a replay will replace the existing replay.

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:

  • StartingPoint (Required) – Signals where to start replaying messages from.

  • EndingPoint (Optional) – Signals when to stop replaying messages. If EndingPoint is omitted, then the replay will continue until caught up to the current time.

  • PointType (Required) – Sets the type of starting and ending points. Currently, the supported value for PointType is Timestamp.

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 Amazon SDK, you must configure it with your credentials. For more information, see Shared config and credentials files in the Amazon 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-cn: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.

Metric Description

NumberOfReplayedNotificationsDelivered

Provides the subscriber with the aggregate number of messages replayed from the topic archive, at 1-minute resolution.

NumberOfReplayedNotificationsFailed

Provides the subscriber with the aggregate number of messages replayed that failed to deliver from the topic archive, at 1-minute resolution.