Amazon SNS FAQs

Q: What is Amazon Simple Notification Service (Amazon SNS)?

Amazon Simple Notification Service (Amazon SNS) is a web service that makes it easy to set up, operate, and send notifications from the cloud. It provides developers with a highly scalable, flexible, and cost-effective capability to publish messages from an application and immediately deliver them to subscribers or other applications. It is designed to make web-scale computing easier for developers. Amazon SNS follows the “publish-subscribe” (pub-sub) messaging paradigm, with notifications being delivered to clients using a “push” mechanism that eliminates the need to periodically check or “poll” for new information and updates. With simple APIs requiring minimal up-front development effort, no maintenance or management overhead and pay-as-you-go pricing, Amazon SNS gives developers an easy mechanism to incorporate a powerful notification system with their applications.

Q: How can I get started using Amazon SNS?

You can create an Amazon SNS topic and publish messages in a few steps by completing our 10-minute tutorial.

For additional detail, see the Amazon SNS Developer Guide, and sample code in the Resource Center.

Q: What are the benefits of using Amazon SNS?

Amazon SNS offers several benefits making it a versatile option for building and integrating loosely-coupled, distributed applications:

• Instantaneous, push-based delivery (no polling)
• Simple APIs and easy integration with applications
• Flexible message delivery over multiple transport protocols
• Inexpensive, pay-as-you-go model with no up-front costs
• Web-based Amazon Web Services Management Console offers the simplicity of a point-and-click interface
  

Q: What are some example uses for Amazon SNS notifications?

The Amazon SNS service can support a wide variety of needs including event notification, monitoring applications, workflow systems, time-sensitive information updates, mobile applications, and any other application that generates or consumes notifications. For example, Amazon SNS can be used in workflow systems to relay events among distributed computer applications, move data between data stores or update records in business systems. Event updates and notifications concerning validation, approval, inventory changes and shipment status are immediately delivered to relevant system components as well as end-users. A common pattern is to use SNS to publish messages to Amazon SQS message queues to reliably send messages to one or many system components asynchronously. Another example use for Amazon SNS is to relay time-critical events to mobile applications and devices. Since Amazon SNS is both highly reliable and scalable, it provides significant advantages to developers who build applications that rely on real-time events.

Q: How does Amazon SNS work?

It is very easy to get started with Amazon SNS. Developers must first create a “topic” which is an “access point” – identifying a specific subject or event type – for publishing messages and allowing clients to subscribe for notifications. Once a topic is created, the topic owner can set policies for it such as limiting who can publish messages or subscribe to notifications, or specifying which notification protocols will be supported (i.e. HTTP/HTTPS, SQS, Lambda). Subscribers are clients interested in receiving notifications from topics of interest; they can subscribe to a topic or be subscribed by the topic owner. Subscribers specify the protocol and end-point (URL, email address, etc.) for notifications to be delivered. When publishers have information or updates to notify their subscribers about, they can publish a message to the topic – which immediately triggers Amazon SNS to deliver the message to all applicable subscribers.

Q: How is Amazon SNS different from Amazon SQS?

Amazon Simple Queue Service (SQS) and Amazon SNS are both messaging services within Amazon Web Services, which provide different benefits for developers. Amazon SNS allows applications to send time-critical messages to multiple subscribers through a “push” mechanism, eliminating the need to periodically check or “poll” for updates. Amazon SQS is a message queue service used by distributed applications to exchange messages through a polling model, and can be used to decouple sending and receiving components. Amazon SQS provides flexibility for distributed components of applications to send and receive messages without requiring each component to be concurrently available.

A common pattern is to use SNS to publish messages to Amazon SQS queues to reliably send messages to one or many system components asynchronously.

Q: How is Amazon SNS different from Amazon MQ?

Amazon MQ, Amazon SQS, and Amazon SNS are messaging services that are suitable for anyone from startups to enterprises. If you're using messaging with existing applications, and want to move your messaging to the cloud quickly and easily, we recommend you consider Amazon MQ. It supports industry-standard APIs and protocols so you can switch from any standards-based message broker to Amazon MQ without rewriting the messaging code in your applications. If you are building brand new applications in the cloud, we recommend you consider Amazon SQS and Amazon SNS. Amazon SQS and SNS are lightweight, fully managed message queue and topic services that scale almost infinitely and provide simple, easy-to-use APIs. You can use Amazon SQS and SNS to decouple and scale microservices, distributed systems, and serverless applications, and improve reliability.

Q: How can I get started using Amazon SNS?

To sign up for Amazon SNS, click the “Sign up for Amazon SNS” button on the Amazon SNS detail page. You must have an Amazon Web Services account to access this service; if you do not already have one, you will be prompted to create one when you begin the Amazon SNS sign-up process. After signing up, please refer to the Amazon SNS documentation and Getting Started Guide to begin using Amazon SNS. Using the Amazon Web Services Management Console, you can easily create topics, add subscribers, send notifications, and edit topic policies – all from your browser.

Q: Is Amazon SNS supported in the Amazon Web Services Management Console?

Amazon SNS is supported in the Amazon Web Services Management Console which provides a point-and-click, web-based interface to access and manage Amazon SNS. Using the Amazon Web Services Management Console, you can create topics, add subscribers, and send notifications – all from your browser. In addition, the Amazon Web Services Management Console makes it easy to publish messages to your endpoint of choice (HTTP, SQS, Lambda, or email) and edit topic policies to control publisher and subscriber access.

Q: What are the Amazon SNS service access endpoints in each region?

Please refer to the Amazon Web Services Regions and Endpoints section of the Amazon Web Services documentation for the latest list of all Amazon SNS service access points.

Q: Can I get a history of SNS API calls made on my account for security analysis and operational troubleshooting purposes?

Yes. SNS supports Amazon CloudTrail, a web service that records Amazon API calls for your account and delivers log files to you. With CloudTrail, you can obtain a history of such information as the identity of the API caller, the time of the API call, the source IP address of the API caller, the request parameters, and the response elements returned by SNS.

SNS currently supports CloudTrail auditing for authenticated calls only. CloudTrail Audit logs for unauthenticated ConfirmSubscription and Unsubscribe calls are not available at this time. For more information, see the CloudTrail section of the SNS Developer Guide.

To receive a history of SNS API calls made on your account, simply turn on Amazon CloudTrail in the Amazon Web Services Management Console. To learn more about Amazon CloudTrail, click here. 

Q: How will I be charged and billed for my use of Amazon SNS?

There are no set-up fees to begin using the service. At the end of the month, your credit card will automatically be charged for that month’s usage. You can view your charges for the current billing period at any time on the Amazon Web Services web site by logging into your Amazon Web Services account and clicking “Account Activity” under “Your Web Services Account”.

Q: When does billing of my Amazon SNS use begin and end?

Your Amazon SNS billing cycle begins on the first day of each month and ends on the last day of each month. Your monthly charges will be totaled at the end of each month.

Q: What is the format of an Amazon SNS topic?

Topic names are limited to 256 characters. Alphanumeric characters plus hyphens (-) and underscores (_) are allowed. Topic names must be unique within an Amazon Web Services account. After you delete a topic, you can reuse the topic name. When a topic is created, Amazon SNS will assign a unique ARN (Amazon Web Services Resource Name) to the topic, which will include the service name (SNS), region, Amazon Web Services ID of the user and the topic name. The ARN will be returned as part of the API call to create the topic. Whenever a publisher or subscriber needs to perform any action on the topic, they should reference the unique topic ARN.

Q: What are the available operations for Amazon SNS and who can perform these operations?

Amazon SNS provides a set of simple APIs to enable event notifications for topic owners, subscribers, and publishers.

Owner operations:

• CreateTopic – Create a new topic.
• DeleteTopic – Delete a previously created topic.
• ListTopics – List of topics owned by a particular user (Amazon Web Services ID).
• ListSubscriptionsByTopic – List of subscriptions for a particular topic
• SetTopicAttributes – Set/modify topic attributes, including setting and modifying publisher/subscriber permissions, transports supported, etc.
• GetTopicAttributes – Get/view existing attributes of a topic
• AddPermission – Grant access to selected users for the specified actions
• RemovePermission – Remove permissions for selected users for the specified actions

Subscriber operations:

• Subscribe – Register a new subscription on a particular topic, which will generate a confirmation message from Amazon SNS
• ConfirmSubscription – Respond to a subscription confirmation message, confirming the subscription request to receive notifications from the subscribed topic
• UnSubscribe – Cancel a previously registered subscription
• ListSubscriptions – List subscriptions owned by a particular user (Amazon Web Services ID)

Publisher operations:

• Publish: Publish a new message to the topic.

Q: Why are there two different APIs to list subscriptions?

The two APIs to list subscriptions perform different functions and return different results:

The ListSubscriptionsByTopic API allows a topic owner to see the list of all subscribers actively registered to a topic.

The ListSubscriptions API allows a user to get a list of all their active subscriptions (to one or more topics).

Q: What are the different delivery formats/transports for receiving notifications?

• “SQS” – Users can specify an SQS standard or FIFO queue as the endpoint; Amazon SNS will enqueue a notification message to the specified queue (which subscribers can then process using SQS APIs such as ReceiveMessage, DeleteMessage, etc.).
• “HTTP”, “HTTPS” – Subscribers specify a URL as part of the subscription registration; notifications will be delivered through an HTTP POST to the specified URL.
• ”Email”, “Email-JSON” – Messages are sent to registered addresses as email. Email-JSON sends notifications as a JSON object, while Email sends text-based email.
• “SQS” – Users can specify an SQS standard queue as the endpoint; Amazon SNS will enqueue a notification message to the specified queue (which subscribers can then process using SQS APIs such as ReceiveMessage, DeleteMessage, etc.).

Q: Can topic owners control the transports that are allowed on topics they create/own?

Topic owners can configure specific transports on their topics by setting the appropriate permissions through access control policies.

Q: How does an owner set Access Control policies?

Please refer to the Amazon SNS Getting Started Guide for an overview of setting access control policies.

Q: Can a single topic support subscriptions over multiple protocols/transports?

Subscribers to an Amazon SNS topic can receive notifications on any transport supported by the topic. A topic can support subscriptions and notification deliveries over multiple transports.

Q: Can subscribers selectively receive only a subset of messages published to a topic?

Yes, you can use message filtering on Amazon Simple Notification Service (SNS) to build simpler and more streamlined pub/sub architectures. Message filtering enables Amazon SNS topic subscribers to selectively receive only a subset of the messages they are interested in, as opposed to receiving all messages published to a topic. To monitor the usage of SNS subscription filter policies, use Amazon CloudWatch metrics, which are automatically collected for you. You can also use the Amazon::SNS::Subscription resource type in Amazon CloudFormation templates to quickly deploy solutions that use SNS message filtering. For more details, see the Filter Messages with Amazon SNS section in our documentation.

Q: Can Amazon SNS be used with other Amazon Web Services services?

Amazon SNS can be used with other Amazon Web Services services such as Amazon SQS, Amazon EC2 and Amazon S3. Here is an example of how an order processing workflow system uses Amazon SNS with Amazon EC2, SQS, and SimpleDB. In this workflow system, messages are sent between application components whenever a transaction occurs or an order advances through the order processing pipeline. When a customer initially places an order, the transaction is first recorded in Amazon SimpleDB and an application running on Amazon EC2 forwards the order request to a payment processor which debits the customer’s credit card or bank account. Once approved, an order confirmation message is published to an Amazon SNS topic. In this case, the topic has various subscribers over Email/HTTP – merchant, customer and supply chain partners – and notifications sent by Amazon SNS for that topic can instantly update all of them that payment processing was successful. Notifications can also be used to orchestrate an order processing system running on EC2, where notifications sent over HTTP can trigger real-time processing in related components such as an inventory system or a shipping service. By integrating Amazon SNS with Amazon SQS, all notifications delivered are also persisted in an Amazon SQS queue where they are processed by an auditing application at a future time.

Q: Is Amazon SNS available in all regions where Amazon Web Services services are available?

Please refer to the Amazon Web Services Regions and Endpoints section of the Amazon Web Services documentation for the most up to date information on Amazon SNS availability.

Q: How soon can customers recreate topics with previously used topic names?

Topic names should typically be available for reuse approximately 30-60 seconds after the previous topic with the same name has been deleted. The exact time will depend on the number of subscriptions which were active on the topic – topics with a few subscribers will be available instantly for reuse, topics with larger subscriber lists may take longer.

Q: What are SNS FIFO topics?

Similar to standard SNS topics, SNS FIFO topics allow users to publish a message to a topic, so it can be delivered to a series of subscribing endpoints. When the delivery of those messages to subscribers must be in order (first-in-first-out), and once only, and you want SNS to take care of it, SNS FIFO topics is the way to go. Amazon SNS FIFO topics deliver ordered messages to Amazon Simple Queue Service (Amazon SQS) FIFO queues to provide consistent end-to-end message ordering for distributed applications. You can now reduce the effort required to process your high throughput, consistently ordered transactions and simplify your messaging architecture. Example use cases include bank transaction logs, stock tickers, flight trackers, price updates, news broadcasting, and inventory management.

Q: When should I use SNS FIFO topics and when should I use Kinesis Data Streams?

Both SNS FIFO topics and Kinesis Streams enable you to build applications that require strictly ordered, many-to-many messaging. SNS FIFO topics can further unlock application integration use cases that require large ordered fan-out, up to 100 subscribers. Kinesis Streams, on the other hand, supports ordered fan-out up to 5 subscribers and is often used for analytics and anomaly detection use cases.

Q: How would a user subscribe for notifications to be delivered over email?

To receive email notifications for a particular topic, a subscriber should specify “Email” or “Email-JSON” as the protocol and provide a valid email address as the end-point. This can be done using the Amazon Web Services Management Console or by calling the Amazon SNS API directly. Amazon SNS will then send an email with a confirmation link to the specified email address, and require the user monitoring the email address to explicitly opt-in for receiving email notifications from that particular topic. Once the user confirms the subscription by clicking the provided link, all messages published to the topic will be delivered to that email address.

Q: Why does Amazon SNS provide two different transports to receive notifications over email?

The two email transports are provided for two distinct types of customers/end-users. “Email-JSON” sends notifications as a JSON object, and is meant for applications to programmatically process emails. The ”Email” transport is meant for end-users/consumers and notifications are regular, text-based messages which are easily readable.

Q: Can a user change the Subject and Display name for notifications sent over Email/Email-JSON?

Amazon SNS allows users to specify the Subject field for emails as a parameter passed in to the Publish API call and can be different for every message published. The Display name for topics can be set using the SetTopicAttributes API – this name applies to all emails sent from this topic.

Q: Do subscribers need to specifically configure their email settings to receive notifications from Amazon SNS?

In most cases, users should be able to receive subscription confirmations and notifications from Amazon SNS without doing anything specific. However, there could be cases where the email provider’s default settings or other user-specific configurations mistakenly redirect the emails to the junk/spam folder.

Q: In the case of passing in an SQS queue as an endpoint, will users need to create the queue prior to subscribing? What permissions will the queue require?

Using the SQS console, users should create the SQS queue prior to subscribing it to a Topic. Select this queue on the console, and from the ‘Queue Actions’ in the menu bar, select ‘Subscribe Queue to SNS Topic’ from the drop-down list. In the subscribe dialog box, select the topic from the ‘Choose a Topic’ drop-down list, and click the ‘Subscribe’ button. For complete step-by-step instructions, please refer to the Amazon SNS documentation.

Q: How would a developer setup an Amazon SQS queue to receive Amazon SNS notifications?

To have Amazon SNS deliver notifications to an SQS queue, a developer should subscribe to a topic specifying “SQS” as the transport and a valid SQS standard queue as the end-point. In order to allow the SQS queue to receive notifications from Amazon SNS, the SQS queue owner must subscribe the SQS queue to the Topic for Amazon SNS to successfully deliver messages to the queue.

If the user owns both the Amazon SNS topic being subscribed to and the SQS queue receiving the notifications, nothing further is required. Any message published to the topic will automatically be delivered to the specified SQS queue. If the user owning the SQS queue is not the owner of the topic, Amazon SNS will require an explicit confirmation to the subscription request.

Please refer to the Amazon SNS documentation for further details on subscribing an SQS queue to a topic and setting access control policies for SQS queues.

Q: How can I fanout identical messages to multiple SQS queues?

Create an SNS topic first using SNS. Then create and subscribe multiple SQS standard queues to the SNS topic. Now whenever a message is sent to the SNS topic, the message will be fanned out to the SQS queues, i.e. SNS will deliver the message to all the SQS queues that are subscribed to the topic.

Q: What is the format of structured notification messages sent by Amazon SNS?

The notification message sent by Amazon SNS for deliveries over HTTP, HTTPS, Email-JSON and SQS transport protocols will consist of a simple JSON object, which will include the following information:

• MessageId: A Universally Unique Identifier, unique for each notification published.
• Timestamp: The time (in GMT) at which the notification was published.
• TopicArn: The topic to which this message was published
• Type: The type of the delivery message, set to “Notification” for notification deliveries.
• UnsubscribeURL: A link to unsubscribe the end-point from this topic, and prevent receiving any further notifications.
• Message: The payload (body) of the message, as received from the publisher.
• Subject: The Subject field – if one was included as an optional parameter to the publish API call along with the message.
• Signature: Base64-encoded “SHA1withRSA” signature of the Message, MessageId, Subject (if present), Type, Timestamp, and Topic values.
• SignatureVersion: Version of the Amazon SNS signature used.

Notification messages sent over the “Email” transport only contain the payload (message body) as received from the publisher.

Q: How can users secure the messages sent to my topics?

All API calls made to Amazon SNS are validated for the user’s Amazon Web Services ID and the signature. In addition, we recommend that users secure their data over the wire by connecting to our secure SSL end-points.

Q: Who can create a topic?

Topics can only be created by users with valid Amazon Web Services IDs who have signed up for Amazon SNS. The easiest way to create a topic is to use the Amazon Web Services Management Console. It can also be created through the CreateTopic API. The Amazon Web Services Management Console is available at: https://console.amazonaws.cn/

Q: Can multiple users publish to a single topic?

A topic owner can set explicit permissions to allow more than one user (with a valid Amazon Web Services ID) to publish to a topic. By default, only topic owners have permissions to publish to a topic.

Q: How can the owner grant/revoke publish or subscribe permissions on a topic?

The AddPermission and RemovePermission APIs provide a simple interface for developers to add and remove permissions for a topic. However, for conditional access and more advanced use cases, users should use access control policies to manage permissions. The easiest way to manage permissions is to use the Amazon Web Services Management Console. The Amazon Web Services Management Console is available at: https://console.amazonaws.cn/

Q: How does a topic owner give access to subscribers? Do subscribers have to have valid Amazon Web Services IDs?

Amazon SNS makes it easy for users with and without Amazon Web Services IDs to receive notifications. The owner of the topic can grant/restrict access to subscribers by setting appropriate permissions for the topic using Access Control policies. Users can receive notifications from Amazon SNS in two ways:

• Users with Amazon Web Services IDs: Subscribers with valid Amazon Web Services IDs (please refer to this link for details on obtaining Amazon Web Services IDs) can subscribe to any topic directly – as long as the topic owner has granted them permissions to do so. The Amazon Web Services IDs will be validated as part of the subscription registration.
• Other users: Topic owners can subscribe and register end-points on behalf of users without Amazon Web Services IDs.

In both cases, the owner of the subscription endpoint needs to explicitly opt-in and confirm the subscription by replying to confirmation message sent by Amazon SNS.

Q: How will Amazon SNS authenticate API calls?

All API calls made to Amazon SNS will validate authenticity by requiring that requests be signed with the secret key of the Amazon Web Services ID account and verifying the signature included in the requests.

Q: How does Amazon SNS validate a subscription request to ensure that notifications will not be sent to users as spam?

As part of the subscription registration, Amazon SNS will ensure that notifications are only sent to valid, registered subscribers/end-points. To prevent spam and ensure that a subscriber end-point is really interested in receiving notifications from a particular topic, Amazon SNS requires an explicit opt-in from subscribers using a 2-part handshake:

i. When a user first calls the Subscribe API and subscribes an end-point, Amazon SNS will send a confirmation message to the specified end-point.

ii. On receiving the confirmation message at the end-point, the subscriber should confirm the subscription request by sending a valid response. Only then will Amazon SNS consider the subscription request to be valid. If there is no response to the challenge, Amazon SNS will not send any notifications to that end-point. The exact mechanism of confirming the subscription varies by the transport protocol selected:

• For HTTP/HTTPS notifications, Amazon SNS will first POST the confirmation message (containing a token) to the specified URL. The application monitoring the URL will have to call the ConfirmSubscription API with the token included token.
• For Email and Email-JSON notifications, Amazon SNS will send an email to the specified address containing an embedded link. The user will need to click on the embedded link to confirm the subscription request.
• For SQS notifications, Amazon SNS will enqueue a challenge message containing a token to the specified queue. The application monitoring the queue will have to call the ConfirmSubscription API with the token.

Note: The explicit “opt-in” steps described above are not required for the specific case where you subscribe your Amazon SQS queue to your Amazon SNS topic – and both are “owned” by the same Amazon Web Services account.

Q: How long will subscription requests remain pending, while waiting to be confirmed?

Token included in the confirmation message sent to end-points on a subscription request are valid for 3 days.

Q: Who can change permissions on a topic?

Only the owner of the topic can change permissions for that topic.

Q: How can users verify that notification messages are sent from Amazon SNS?

To ensure the authenticity of the notifications, Amazon SNS will sign all notification deliveries using a cryptographically secure, asymmetric mechanism (private-public key pair based on certificates). Amazon SNS will publish its certificate to a well-known location and sign messages with the private key of that certificate. Developers/applications can obtain the certificate and validate the signature in the notifications with the certificate’s public key, to ensure that the notification was indeed sent out by Amazon SNS. For further details on certificate locations, please refer to the Amazon SNS details page.

Q: Do publishers have to sign messages as well?

Amazon SNS requires publishers with Amazon Web Services IDs to validate their messages by signing messages with their secret Amazon Web Services key; the signature is then validated by Amazon SNS.

Q: Can a publisher/subscriber use SSL to secure messages?

Yes, both publishers and subscribers can use SSL to help secure the channel to send and receive messages. Publishers can connect to Amazon SNS over HTTPS and publish messages over the SSL channel. Subscribers should register an SSL-enabled end-point as part of the subscription registration, and notifications will be delivered over a SSL channel to that end-point.

Q: What permissions does a subscriber need to allow Amazon SNS to send notifications to a registered endpoint?

The owner of the end-point receiving the notifications has to grant permissions for Amazon SNS to send messages to that end-point.

Q: How can subscriptions be unsubscribed?

Subscribers can be unsubscribed either by the topic owner, the subscription owner or others – depending on the mechanism used for confirming the subscription request.

• A subscription that was confirmed with the AuthenticateOnUnsubscribe flag set to True in the call to the ConfirmSubscription API call can only be unsubscribed by a topic owner or the subscription owner.
• If the subscription was confirmed anonymously without the AuthenticateOnUnsubscribe flag set to True, then it can be anonymously unsubscribed.

In all cases except when unsubscribed by the subscription owner, a final cancellation message will be sent to the end-point, allowing the endpoint owner to easily re-subscribe to the topic (if the Unsubscribe request was unintended or in error). For further details on the ConfirmSubscription API, please refer to the Amazon SNS documentation.

Q: How durable is my data once published to Amazon SNS?

SNS provides durable storage of all messages that it receives. Upon receiving a publish request, SNS stores multiple copies (to disk) of the message across multiple Availability Zones before acknowledging receipt of the request to the sender. Each Amazon Web Services Region has multiple, isolated locations known as Availability Zones. Although rare, should a failure occur in one zone, the operation of SNS and the durability of your messages continue without disruption.

Q: Will a notification contain more than one message?

No, all notification messages will contain a single published message.

Q: How many times will a subscriber receive each message?

Although most of the time each message will be delivered to your application exactly once, the distributed nature of Amazon SNS and transient network conditions could result in occasional, duplicate messages at the subscriber end. Developers should design their applications such that processing a message more than once does not create any errors or inconsistencies.

Q: Will messages be delivered to me in the exact order they were published?

The Amazon SNS service will attempt to deliver messages from the publisher in the order they were published into the topic. However, network issues could potentially result in out-of-order messages at the subscriber end.

Q: Can a message be deleted after being published?

No, once a message has been successfully published to a topic, it cannot be recalled.

Q: Does Amazon SNS guarantee that messages are delivered to the subscribed endpoint?

Yes, as long as the subscribed endpoint is accessible. A message delivery fails when Amazon SNS can't access a subscribed endpoint, due to either a client-side or a server-side error. A client-side error happens when the subscribed endpoint has been deleted by the endpoint owner, or when its access permissions have changed in a way that prevents Amazon SNS from delivering messages to this endpoint. A server-side error happens when the service that powers the subscribed endpoint is unavailable, such as Amazon SQS or Amazon Lambda. When Amazon SNS receives a client-side error, or continues to receive a server-side error for a message beyond the number of retries specified by the corresponding retry policy, Amazon SNS discards the message — unless a dead-letter queue is attached to the subscription. For more information, see Message Delivery Retries. and Amazon SNS Dead-Letter Queues.

Q: What happens to Amazon SNS messages if the subscribing endpoint is not available?

If a message cannot be successfully delivered on the first attempt, Amazon SNS executes a 4-phase retry policy: 1) retries with no delay in between attempts, 2) retries with minimum delay between attempts, 3) retries according to a back-off model, and 4) retries with maximum delay between attempts. When the message delivery retry policy is exhausted, Amazon SNS can move the message to a dead-letter queue (DLQ). For more information, see Message Delivery Retries and Amazon SNS Dead-Letter Queues.

Q: Are there quotas for the number of topics or number of subscribers per topic?

By default, SNS offers 10 million subscriptions per topic, and 100,000 topics per account. To request a higher quota, please contact Support.

Q: How much and what kind of data can go in a message?

Amazon SNS messages can contain up to 256 KB of text data, including XML, JSON and unformatted text.

The following Unicode characters are accepted:

#x9 | #xA | #xD | [#x20 to #xD7FF] | [#xE000 to #xFFFD] | [#x10000 to #x10FFFF]

Each 64KB chunk of published data is billed as 1 request. For example, a single API call with a 256KB payload will be billed as four requests.

Q: How many message filters can be applied to a topic?

By default, 200 filter policies per account per region can be applied to a topic. Please contact us if more is required.

Q: What is raw message delivery?

You can opt-in to get your messages delivered in raw form, i.e. exactly as you published them. By default, messages are delivered encoded in JSON that provides metadata about the message and topic. Raw message delivery can be enabled by setting the “RawMessageDelivery” property on the subscriptions. This property can be set by using the Amazon Web Services Management Console, or by using the API SetSubscriptionAttributes.

Q: What is the default behavior if the raw message delivery property on the subscription is not set?

By default, if this property is not set, messages will be delivered in JSON format, which is the current behavior. This ensures existing applications will continue to operate as expected.

Q: Which types of endpoints support raw message delivery?

Raw message delivery support is supported with SQS and HTTP(S) endpoints. Deliveries to Lambda, and email endpoints will behave the same independent of the “RawMessageDelivery” property.

Q: How will raw messages be delivered to HTTP endpoints?

When raw-formatted messages are delivered to HTTP/s endpoints, the message body will be included in the body of the HTTP POST.

Q: What does support for Amazon Lambda endpoints in Amazon SNS mean?

You can invoke your Amazon Lambda functions by publishing messages to Amazon SNS topics that have Amazon Lambda functions subscribed to them. Because Amazon SNS supports message fan-out, publishing a single message can invoke different Amazon Lambda functions or invoke Lambda functions in addition to delivering notifications to supported Amazon SNS destinations such as HTTP endpoints, SQS, and email.

Q: What is Amazon Lambda?

Amazon Lambda is a compute service that runs your code in response to events and automatically manages the compute resources for you, making it easy to build applications that respond quickly to new information. More information on Amazon Lambda and how to create Amazon Lambda functions can be found here.

Q: What can I do with Amazon Lambda functions and Amazon SNS?

By subscribing Amazon Lambda functions to Amazon SNS topics, you can perform custom message handling. You can invoke an Amazon Lambda function to provide custom message delivery handling by first publishing a message to an Amazon Lambda function, have your Lambda function modify a message (e.g. localize language) and then filter and route those messages to other topics and endpoints. Apps and services that already send Amazon SNS notifications, such as Amazon CloudWatch, can now immediately take advantage of Amazon Lambda without having to provision or manage infrastructure for custom message handling. You can also use delivery to an Amazon Lambda function as a way to publish to other Amazon Web Services services such as Amazon Kinesis or Amazon S3. You can subscribe an Amazon Lambda function to the Amazon SNS topic, and then have the Lambda function in turn write to another service.

Q: How do I activate Amazon Lambda endpoint support in Amazon SNS?

You need to first create an Amazon Lambda function via your Amazon Web Services account and the  Amazon Lambda console, and then subscribe that Amazon Lambda function to a topic using the Amazon SNS console or the Amazon SNS APIs. Once that is complete, any messages that you publish to the Amazon SNS topics which have Lambda functions subscribed to them will be delivered to the appropriate Lambda functions in addition to any other destinations subscribed to that topic.

Q: What does delivery of a message from Amazon SNS to an Amazon Lambda function do?

A message delivery from Amazon SNS to an Amazon Lambda function creates an instance of the Amazon Lambda function and invokes it with your message as an input. For more information on message formats, please refer to the Amazon SNS documentation and the Amazon Lambda documentation.

Q: How much does this feature cost?

Publishing a message with Amazon SNS costs ¥3.40 per million requests. Aside from charges incurred in using Amazon Web Services services, there are no additional fees for delivering a message to an Amazon Lambda function. Amazon SNS has a Free Tier of 1 million requests per month. For more information, please refer to Amazon SNS pricing. Amazon Lambda function costs are based on the number of requests for your functions and the time your code executes. The Amazon Lambda Free-Tier includes 1M requests per month and 400,000 GB-seconds of compute time per month. For more information, please refer to  Amazon Lambda pricing.

Q: Can I subscribe Amazon Lambda functions created by someone else to Amazon SNS topics that I own?

We currently do not allow an Amazon Web Services account owner to subscribe an Amazon Lambda function that belongs to another account. You can subscribe your own Amazon Lambda functions to your own Amazon SNS topics or subscribe your Amazon Lambda functions to an Amazon SNS topic that was created by another account so long as the topic policy for that SNS topic allows it.

Q: Is there a quota to the number of Amazon Lambda functions that I can subscribe to an Amazon SNS topic?

Amazon SNS treats Amazon Lambda functions like any other destination. By default, SNS offers 10 million subscriptions per topic.

Q: What data can I pass to my Amazon Lambda function?

When an Amazon Lambda function is invoked as a result of an Amazon SNS message delivery, the Amazon Lambda function receives data such as the Message ID, the topic ARN, the message payload, and message attributes via an SNS Event.

Q: Can I track delivery status for message delivery attempts to Amazon Lambda functions?

To track the success or failure status of message deliveries, you need to activate the Delivery Status feature of Amazon SNS. For more information about how to activate this feature please read our blog.

Q: What regions is Amazon Lambda available in?

See Amazon Web Services Regions and Endpoints for a complete list.

Q: Do my Amazon Lambda functions need to be in the same region as my Amazon SNS usage?

You can subscribe your Amazon Lambda functions to an Amazon SNS topic in any region.

Q: Are there any data transfer costs for invoking Amazon Lambda functions?

Data transfer costs are applicable to message deliveries to Amazon Lambda functions. Please refer to our pricing for more information.

Q: Are there any quotas to the concurrency of Amazon Lambda functions?

Amazon Lambda currently supports 1000 concurrent executions per Amazon Web Services account per region. If your Amazon SNS message deliveries to Amazon Lambda contribute to crossing these concurrency quotas, your Amazon SNS message deliveries will be throttled. If Amazon Lambda throttles an Amazon SNS message, Amazon SNS will retry the delivery attempts. For more information about Amazon Lambda concurrency quotas, please refer to Amazon Lambda documentation.

Q: Can Amazon SNS use the same Amazon Lambda functions that I use with other services (e.g. Amazon S3)?

You can use the same   Amazon Lambda functions that you use with other services as long as the same function can parse the event formats from Amazon SNS in addition to the event format of the other services.