Hello, learners! In today's lesson, we'll delve deeper into AWS Simple Notification Service (SNS). As you might remember, we touched upon SNS in our overview of AWS messaging services. The core concept we need to master in AWS SNS is 'Topics'. SNS Topics are simply communication channels, where messages can be published, and subscribers to these topics receive these messages. Our focus today will primarily be on these 'Topics'.

AWS SNS Topics are a pivotal part of the Amazon Simple Notification Service. They enable you to group multiple recipients under a common area of interest, assigning a unique endpoint to each entity subscribed. Here are some important details to take note of:

• You can create up to 100,000 SNS Topics per AWS account.
• Each topic can support deliveries of up to 100,000,000 messages per day!
• Messages, or 'payloads', should not be more than 256KB in size.
• You can have nearly 12.5 million immediate subscriptions per topic!

Subscribers to an SNS topic can be various types of endpoints, such as:

• HTTP/S endpoints: A web-based or internet-accessible endpoint.
• Email (Text or JSON): Notifications via email in a raw, free-form text format, or a structured, JSON-formatted message.
• Amazon SQS Queues: Messages can be queued for one or more recipients to pull and process as needed.
• AWS Lambda functions: Subscriptions can trigger a Lambda function when new messages are published to the topic.
• SMS: Notifications sent as text messages directly to a mobile device.
• Mobile app platforms(like Google’s FCM, Apple's APNS, Amazon’s ADM, etc.): Primarily used for push messaging to mobile apps.
• AWS Managed service endpoints: Services like Amazon Simple Storage Service (S3), Amazon EC2 Systems Manager, AWS CloudFormation, AWS CloudWatch, can also receive notifications from SNS.