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AWS SQS & SNS — Messaging Services

AWS SQS & SNS — Messaging Services

AWS provides two core messaging services for decoupling application components:

SQS (Simple Queue Service) — Message queue for point-to-point communication
SNS (Simple Notification Service) — Pub/sub topic-based messaging for fan-out

In Azure terms: SQS ≈ Azure Storage Queues / Azure Service Bus Queue, SNS ≈ Azure Service Bus Topics / Event Grid

SQS — Simple Queue Service

SQS is a fully managed message queue that decouples producers from consumers. Producers send messages; consumers poll and process them at their own pace.

Queue Types

Type	Description
Standard Queue	At-least-once delivery, best-effort ordering, nearly unlimited throughput
FIFO Queue	Exactly-once delivery, strict ordering, up to 3,000 messages/second

Key SQS Concepts

Concept	Description
Message	The data payload (up to 256 KB; use S3 + pointer for larger)
Visibility Timeout	How long a received message is hidden from other consumers (default 30s)
Dead Letter Queue (DLQ)	Receives messages that failed processing after N attempts
Message Retention	1 minute to 14 days (default 4 days)
Long Polling	Consumer waits up to 20s for a message — reduces empty responses and cost
Delay Queue	Delay delivery of new messages by 0–900 seconds

SQS Message Lifecycle

Producer → Queue → Consumer picks up (message hidden)
                         ↓ Processing succeeds → Delete message
                         ↓ Processing fails × N → Move to DLQ

SQS CLI Examples

# Create a standard queue
aws sqs create-queue --queue-name my-queue

# Send a message
aws sqs send-message \
  --queue-url https://sqs.us-east-1.amazonaws.com/123456789/my-queue \
  --message-body "Hello from SQS"

# Receive messages (long poll)
aws sqs receive-message \
  --queue-url https://sqs.us-east-1.amazonaws.com/123456789/my-queue \
  --wait-time-seconds 10 \
  --max-number-of-messages 5

# Delete a message after processing
aws sqs delete-message \
  --queue-url https://sqs.us-east-1.amazonaws.com/123456789/my-queue \
  --receipt-handle "abc123..."

SNS — Simple Notification Service

SNS is a fully managed pub/sub messaging service. Publishers send messages to a Topic, and SNS fans out to all subscribers simultaneously.

Subscriber Type	Use Case
SQS	Fan out to multiple queues for parallel processing
Lambda	Trigger serverless functions
HTTP/HTTPS	Webhooks to external services
Email / Email-JSON	Notifications to people
SMS	Text messages to phones
Mobile Push	iOS (APNs), Android (FCM), Fire OS notifications
Amazon Kinesis Data Firehose	Stream data to S3, Redshift, etc.

Fan-Out Pattern (SNS + SQS)

Order Service
     ↓ publishes to SNS Topic
     ├─→ SQS Queue → Inventory Lambda (update stock)
     ├─→ SQS Queue → Email Lambda (send confirmation)
     └─→ SQS Queue → Analytics Lambda (log event)

This pattern decouples services while ensuring each consumer gets every message.

# Create a topic
aws sns create-topic --name my-topic

# Subscribe an email
aws sns subscribe \
  --topic-arn arn:aws:sns:us-east-1:123456789:my-topic \
  --protocol email \
  --notification-endpoint user@example.com

# Subscribe an SQS queue
aws sns subscribe \
  --topic-arn arn:aws:sns:us-east-1:123456789:my-topic \
  --protocol sqs \
  --notification-endpoint arn:aws:sqs:us-east-1:123456789:my-queue

# Publish a message
aws sns publish \
  --topic-arn arn:aws:sns:us-east-1:123456789:my-topic \
  --message "Order #1234 placed" \
  --subject "New Order"

SQS vs SNS — When to Use Which

Scenario	Use
Worker processing jobs from a queue	SQS
Fan out one event to many systems	SNS
Fan out + durable queuing per consumer	SNS → SQS (fan-out pattern)
Email/SMS alerts	SNS
Guaranteed exactly-once delivery + ordering	SQS FIFO
Rate limiting / buffering before processing	SQS

AWS SQS/SNS vs Azure Equivalents

Feature	AWS	Azure
Basic queue	SQS Standard	Azure Storage Queue
Enterprise queue	SQS FIFO	Azure Service Bus Queue
Pub/Sub topics	SNS	Azure Service Bus Topics
Event-driven routing	SNS + EventBridge	Azure Event Grid
Streaming (high-throughput)	Amazon Kinesis	Azure Event Hubs

Useful Links