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](#core-concepts)
• [Common Patterns](#common-patterns)
• [CLI Reference](#cli-reference)
• [Best Practices](#best-practices)
• [Troubleshooting](#troubleshooting)
• [References](#references)

Core Concepts

Topics

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

Topic Types

| Type | Description | Use Case |

|------|-------------|----------|

| Standard | Best-effort ordering, at-least-once | Most use cases |

| FIFO | Strict ordering, exactly-once | Order-sensitive |

Subscription Protocols

| Protocol | Description |

|----------|-------------|

| Lambda | Invoke Lambda function |

| SQS | Send to SQS queue |

| HTTP/HTTPS | POST to endpoint |

| Email | Send email |

| SMS | Send text message |

| Application | Mobile push notification |

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

| Command | Description |

|---------|-------------|

| aws sns create-topic | Create topic |

| aws sns delete-topic | Delete topic |

| aws sns list-topics | List topics |

| aws sns get-topic-attributes | Get topic settings |

| aws sns set-topic-attributes | Update topic settings |

Subscriptions

| Command | Description |

|---------|-------------|

| aws sns subscribe | Create subscription |

| aws sns unsubscribe | Remove subscription |

| aws sns list-subscriptions | List all subscriptions |

| aws sns list-subscriptions-by-topic | List topic subscriptions |

| aws sns confirm-subscription | Confirm pending subscription |

Publishing

| Command | Description |

|---------|-------------|

| aws sns publish | Publish message |

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