SNS - Simple Notification Service

Pub/Sub model
The event produces only sends messages to one SNS topic
Each subscriber to the topic will get all the messages be default (we can filter them, if we want)
We can have up to 10 million subscribers per topic
We cave up to 100K topics
Subscribers to the topic can be:
- SQS
- HTTP/HTTPS
- Lambda
- Emails
- SMS messages
- Mobile Notifications
Many different services integrate with SNS for notifications, fo example:
- CloudWatch (for alarms)
- Auto Scaling Groups notifications
- S3 (bucket events)
- CloudFormation (state changes)
- Etc…
How to publish?
- In order to publish we must create a topic using the SDK
- We may create one or many subscriptions
- We publish data to the topic
Direct Publish (for mobile apps SDK)
- Create a platform application
- Create a platform endpoint
- Publish to the platform endpoint
Direct Publish works with Google GCM, Apple APNS, Amazon ADM

Security

Encryption:
- In-flight encryption using HTTPS API
- At-rest encryption using the KMS keys
- Client-side encryption if the client wants to perform encryption/decryption itself
Access Controls: IAM policies to regulate access to the SNS API
SNS Access Policies (similar to S3 bucket policies):
- Useful for cross-account access to SNS topics
- Useful for allowing other services (S3) to write to an SNS topic

Send a message to multiple SQS queues using SNS
Push one in SNS, receive in all SQS queues which are subscribers
Fully decouples, no data loss
SQS allows for data persistance, delayed processing and retries of work
Ability to add more SQS subscribers over time
SQS queues must have an allow access policy for SNS to be able to write to the queues
SNS cannot send messages to SQS FIFO queues (AWS limitation)!
Use case: send S3 events to multiple queues:
- For the same combination of even type and prefix we can only have one S3 Event rule
- In case we want to send the same S3 event to many SQS queues, we must use SNS fan-out