# Amazon SNS message archiving for FIFO topic owners
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Message archiving provides the ability to archive a single copy of all messages published to your topic. You can store published messages within your topic by enabling the message archive policy on the topic, which enables message archiving for all subscriptions linked to that topic. Messages can be archived for a minimum of one day to a maximum of 365 days.

Additional charges apply when setting an archive policy. For pricing information, see [Amazon SNS pricing](https://aws.amazon.com/sns/pricing/).

## Create a message archive policy using the AWS Management Console
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Use this option to create a new message archive policy using the AWS Management Console.

1. Sign in to the [Amazon SNS console](https://console.aws.amazon.com/sns/home).

1. Choose a topic or create a new one. To learn more about creating topics, see [Creating an Amazon SNS topic](sns-create-topic.md).
**Note**  
Amazon SNS message archiving and replay is only available for application-to-application (A2A) FIFO topics.

1. On the **Edit topic** page, expand the **Archive policy** section.

1. Enable the **Archive policy** feature, and enter the **number of days** for which you want to archive messages in the topic.

1. Choose **Save changes**.

**To view, edit, and deactivate a message archiving topic policy**
+ On the **Topic details** page, the **Retention policy** displays the status of the archive policy, including the number of days for which it is set. Select the **Archive policy** tab to view the following message archive details:
  + **Status** – The archive and replay status appears as **active** when an archive policy is applied. The archive and replay status appears as **inactive** when the archive policy is set to an empty JSON object.
  + **Message retention period** – The specified number of days for message retention.
  + **Archive start date** – The date from which subscribers can replay messages.
  + **JSON preview** – The JSON preview of the archive policy.
+ (Optional) To **edit** an archive policy, go to the topic summary page and choose **Edit**.
+ (Optional) To **deactivate** an archive policy, go to the topic summary page and choose **Edit**. Deactivate the **Archive Policy** and choose **Save changes**.
+ (Optional) To **delete** a topic with an archive policy, you must first deactivate the archive policy as previously described.
**Important**  
To avoid accidental message deletions, you can not delete a topic with an active message archive policy. The topic's message archive policy must be deactivated before the topic can be deleted. When you deactivate a message archive policy, Amazon SNS deletes all of the archived messages. When deleting a topic, subscriptions are removed, and any messages in transit may not be delivered.

## Create a message archive policy using the API
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To create a message archive policy using the API, you need to add the attribute `ArchivePolicy` to your topic. You can set an `ArchivePolicy` using the API actions `CreateTopic` and `SetTopicAttributes`. `ArchivePolicy` has a single value, `MessageRetentionPeriod`, which represents the number of days Amazon SNS retains messages. To activate message archiving for your topic, set the `MessageRetentionPeriod` to an integer value greater than zero. For example, to retain messages in your archive for 30 days, set the `ArchivePolicy` to:

```
{
    "ArchivePolicy": {
        "MessageRetentionPeriod": "30"
    }
}
```

To disable message archiving for your topic, and clear the archive, unset the `ArchivePolicy`, as follows:

```
{}
```

## Create a message archive policy using the SDK
<a name="message-archiving-and-replay-topic-sdk"></a>

To use an AWS SDK, you must configure it with your credentials. For more information, see [Shared `config` and `credentials` files](https://docs.aws.amazon.com/sdkref/latest/guide/file-format.html) in the * AWS SDKs and Tools Reference Guide*.

The following code example shows how to set the `ArchivePolicy` for an Amazon SNS topic to retain all messages published to the topic for 30 days.

```
// Specify the ARN of the Amazon SNS topic to set the ArchivePolicy for.
String topicArn =
    "arn:aws:sns:us-east-2:123456789012:MyArchiveTopic.fifo";

// Set the MessageRetentionPeriod to 30 days for the ArchivePolicy.
String archivePolicy =
    "{\"MessageRetentionPeriod\":\"30\"}";

// Set the ArchivePolicy for the Amazon SNS topic
SetTopicAttributesRequest request = new SetTopicAttributesRequest()
    .withTopicArn(topicArn)
    .withAttributeName("ArchivePolicy")
    .withAttributeValue(archivePolicy);
sns.setTopicAttributes(request);
```

## Create a message archive policy using CloudFormation
<a name="message-archiving-and-replay-topic-cfn"></a>

To create an archive policy using CloudFormation see [https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-sns-topic.html](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-sns-topic.html) in the *AWS CloudFormation User Guide*.

## Grant access to an encrypted archive
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Before a subscriber can begin replaying messages from an encrypted topic, you must complete the following steps. Because past messages are replayed, Amazon SNS needs to be provisioned `Decrypt` access to the KMS key that was used to encrypt the messages in the archive.

1. When you encrypt messages with a KMS key and store them within the topic, you must grant Amazon SNS the ability to decrypt these messages via Key Policy. For more, see [Grant decrypt permissions to Amazon SNS](#message-archiving-and-replay-topic-decrypt-permissions).

1. Enable AWS KMS for Amazon SNS. For more, see [Configuring AWS KMS permissions](sns-key-management.md#sns-what-permissions-for-sse).

**Important**  
When you add the new sections to your KMS key policy, do not change any existing sections in the policy. If encryption is enabled on a topic, and the KMS key is disabled or deleted, or the KMS key policy is not correctly configured for Amazon SNS, Amazon SNS cannot replay messages to your subscribers. 

### Grant decrypt permissions to Amazon SNS
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In order for Amazon SNS to access encrypted messages from within your topic’s archive and replay them to subscribed endpoints, you must enable the Amazon SNS service principle to decrypt these messages.

The following is an example policy that is required to allow the Amazon SNS service principal to decrypt stored messages during a replay of historical messages from within your topic.

```
{
    "Sid": "Allow SNS to decrypt archived messages",
    "Effect": "Allow",
    "Principal": {
        "Service": "sns.amazonaws.com"
    },
    "Action": [
        "kms:Decrypt",
        "kms:GenerateDataKey"
    ],
    "Resource": "*"
}
```

## Monitor message archive metrics using Amazon CloudWatch
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You can monitor archived 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](sns-logging-monitoring.md).


| Metric | Description | 
| --- | --- | 
|  **ApproximateNumberOfMessagesArchived**  |  Provides the topic owner with the aggregate number of messages archived in the topic archive, at 60-minute resolution.  | 
|  **ApproximateNumberOfBytesArchived**   |  Provides the topic owner with the aggregate number of bytes archived, across all messages in the topic archive, at 60-minute resolution.  | 
|  **NumberOfMessagesArchiveProcessing**   |  Provides the topic owner with the number of messages saved to the topic archive during the interval in 1-minute resolution.  | 
|  **NumberOfBytesArchiveProcessing**  |  Provides the topic owner with the aggregate number of bytes saved to the topic archive during the interval in 1-minute resolution.  | 

The `GetTopicAttributes` API has a `BeginningArchiveTime` property, which represents the oldest timestamp at which a subscriber can start a replay. The following represents a sample response for this API action:

```
{
 "ArchivePolicy": {
    "MessageRetentionPeriod": "<integer>"
  },
  "BeginningArchiveTime": "<timestamp>",
  ...
}
```