Sns

AWS SNS

Amazon Simple Notification Service (SNS) is a fully managed pub/sub messaging service for application-to-application (A2A) and application-to-person (A2P) communication.

Table of Contents

• Core Concepts
• Common Patterns
• CLI Reference
• Best Practices
• Troubleshooting
• References

Core Concepts

Topics

Named channels for publishing messages. Publishers send to topics, subscribers receive from topics.

Topic Types

Subscription Protocols

Message Filtering

Route messages to specific subscribers based on message attributes.

Common Patterns

Create Topic and Subscribe

AWS CLI:

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

# Create FIFO topic
aws sns create-topic \
  --name my-topic.fifo \
  --attributes FifoTopic=true

# Subscribe Lambda
aws sns subscribe \
  --topic-arn arn:aws:sns:us-east-1:123456789012:my-topic \
  --protocol lambda \
  --notification-endpoint arn:aws:lambda:us-east-1:123456789012:function:my-function

# Subscribe SQS
aws sns subscribe \
  --topic-arn arn:aws:sns:us-east-1:123456789012:my-topic \
  --protocol sqs \
  --notification-endpoint arn:aws:sqs:us-east-1:123456789012:my-queue

# Subscribe email
aws sns subscribe \
  --topic-arn arn:aws:sns:us-east-1:123456789012:my-topic \
  --protocol email \
  --notification-endpoint user@example.com

boto3:

import boto3

sns = boto3.client('sns')

# Create topic
response = sns.create_topic(Name='my-topic')
topic_arn = response['TopicArn']

# Subscribe Lambda
sns.subscribe(
    TopicArn=topic_arn,
    Protocol='lambda',
    Endpoint='arn:aws:lambda:us-east-1:123456789012:function:my-function'
)

# Subscribe SQS with filter
sns.subscribe(
    TopicArn=topic_arn,
    Protocol='sqs',
    Endpoint='arn:aws:sqs:us-east-1:123456789012:order-queue',
    Attributes={
        'FilterPolicy': '{"event_type": ["order_created", "order_updated"]}'
    }
)

Publish Messages

import boto3
import json

sns = boto3.client('sns')
topic_arn = 'arn:aws:sns:us-east-1:123456789012:my-topic'

# Simple publish
sns.publish(
    TopicArn=topic_arn,
    Message='Hello, World!',
    Subject='Notification'
)

# Publish with attributes (for filtering)
sns.publish(
    TopicArn=topic_arn,
    Message=json.dumps({'order_id': '12345', 'status': 'created'}),
    MessageAttributes={
        'event_type': {
            'DataType': 'String',
            'StringValue': 'order_created'
        },
        'priority': {
            'DataType': 'Number',
            'StringValue': '1'
        }
    }
)

# Publish to FIFO topic
sns.publish(
    TopicArn='arn:aws:sns:us-east-1:123456789012:my-topic.fifo',
    Message=json.dumps({'order_id': '12345'}),
    MessageGroupId='order-12345',
    MessageDeduplicationId='unique-id'
)

Message Filtering

# Add filter policy to subscription
aws sns set-subscription-attributes \
  --subscription-arn arn:aws:sns:us-east-1:123456789012:my-topic:abc123 \
  --attribute-name FilterPolicy \
  --attribute-value '{
    "event_type": ["order_created"],
    "priority": [{"numeric": [">=", 1]}]
  }'

Filter policy examples:

// Exact match
{"event_type": ["order_created", "order_updated"]}

// Prefix match
{"customer_id": [{"prefix": "PREMIUM-"}]}

// Numeric comparison
{"price": [{"numeric": [">=", 100, "<=", 500]}]}

// Exists check
{"customer_id": [{"exists": true}]}

// Anything but
{"event_type": [{"anything-but": ["deleted"]}]}

// Combined
{
  "event_type": ["order_created"],
  "region": ["us-east", "us-west"],
  "priority": [{"numeric": [">=", 1]}]
}

Fan-Out Pattern (SNS to Multiple SQS)

import boto3
import json

sns = boto3.client('sns')
sqs = boto3.client('sqs')

# Create topic
topic = sns.create_topic(Name='orders-topic')
topic_arn = topic['TopicArn']

# Create queues for different processors
queues = {
    'analytics': sqs.create_queue(QueueName='order-analytics')['QueueUrl'],
    'fulfillment': sqs.create_queue(QueueName='order-fulfillment')['QueueUrl'],
    'notification': sqs.create_queue(QueueName='order-notification')['QueueUrl']
}

# Subscribe each queue
for name, queue_url in queues.items():
    queue_arn = sqs.get_queue_attributes(
        QueueUrl=queue_url,
        AttributeNames=['QueueArn']
    )['Attributes']['QueueArn']

    sns.subscribe(
        TopicArn=topic_arn,
        Protocol='sqs',
        Endpoint=queue_arn
    )

# One publish reaches all queues
sns.publish(
    TopicArn=topic_arn,
    Message=json.dumps({'order_id': '12345', 'total': 99.99})
)

Lambda Permission for SNS

aws lambda add-permission \
  --function-name my-function \
  --statement-id sns-trigger \
  --action lambda:InvokeFunction \
  --principal sns.amazonaws.com \
  --source-arn arn:aws:sns:us-east-1:123456789012:my-topic

CLI Reference

Topic Management

Subscriptions

Publishing

Best Practices

Reliability

• Use SQS for durability — SNS is push-based, SQS queues messages
• Implement retries for HTTP/HTTPS endpoints
• Configure DLQ for failed deliveries
• Use FIFO topics for ordering requirements

Security

• Use topic policies to control access
• Enable encryption with SSE
• Use VPC endpoints for private access

# Enable SSE
aws sns set-topic-attributes \
  --topic-arn arn:aws:sns:us-east-1:123456789012:my-topic \
  --attribute-name KmsMasterKeyId \
  --attribute-value alias/my-key

Cost Optimization

• Use message filtering to reduce unnecessary deliveries
• Batch operations where possible
• Monitor and clean up unused topics/subscriptions

Message Design

• Keep messages small (256 KB limit)
• Use message attributes for routing
• Include correlation IDs for tracing

Troubleshooting

Subscription Not Receiving Messages

Check:

1. Subscription is confirmed (not pending)
2. Filter policy matches message attributes
3. Target permissions (Lambda, SQS)

# Check subscription status
aws sns list-subscriptions-by-topic \
  --topic-arn arn:aws:sns:us-east-1:123456789012:my-topic

# Check subscription attributes
aws sns get-subscription-attributes \
  --subscription-arn arn:aws:sns:us-east-1:123456789012:my-topic:abc123

HTTP Endpoint Not Working

Debug:

# Check delivery status logging
aws sns set-topic-attributes \
  --topic-arn arn:aws:sns:us-east-1:123456789012:my-topic \
  --attribute-name DeliveryPolicy \
  --attribute-value '{
    "http": {
      "defaultHealthyRetryPolicy": {
        "minDelayTarget": 20,
        "maxDelayTarget": 20,
        "numRetries": 3,
        "numMaxDelayRetries": 0,
        "numNoDelayRetries": 0,
        "numMinDelayRetries": 0,
        "backoffFunction": "linear"
      }
    }
  }'

Messages Not Matching Filter

Verify:

• Message attributes are set (not in body)
• Attribute types match (String vs Number)
• Filter policy syntax is correct

# Correct: attributes must be message attributes
sns.publish(
    TopicArn=topic_arn,
    Message='body content',
    MessageAttributes={
        'event_type': {
            'DataType': 'String',
            'StringValue': 'order_created'  # This is filtered
        }
    }
)

# Wrong: this won't be filtered
sns.publish(
    TopicArn=topic_arn,
    Message=json.dumps({'event_type': 'order_created'})  # Not filtered
)

SQS Not Receiving from SNS

Check SQS queue policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {"Service": "sns.amazonaws.com"},
      "Action": "sqs:SendMessage",
      "Resource": "arn:aws:sqs:us-east-1:123456789012:my-queue",
      "Condition": {
        "ArnEquals": {
          "aws:SourceArn": "arn:aws:sns:us-east-1:123456789012:my-topic"
        }
      }
    }
  ]
}

References

• SNS Developer Guide
• SNS API Reference
• SNS CLI Reference
• boto3 SNS