SNS topics and subscriptions in AWS - Commands & Configuration

Introduction

SNS helps send messages to many people or systems at once. It solves the problem of notifying multiple receivers quickly and reliably.

When you want to send alerts to multiple team members by email or SMS at the same time.

When your app needs to notify other apps or services about events instantly.

When you want to fan out messages to many subscribers without coding each connection.

When you want to decouple parts of your system so they communicate by messages.

When you want to send messages to mobile devices or HTTP endpoints automatically.

Config File - sns-topic-subscription.json

sns-topic-subscription.json

{
  "Resources": {
    "MySNSTopic": {
      "Type": "AWS::SNS::Topic",
      "Properties": {
        "TopicName": "example-topic"
      }
    },
    "MySubscription": {
      "Type": "AWS::SNS::Subscription",
      "Properties": {
        "Endpoint": "[e-mail]",
        "Protocol": "email",
        "TopicArn": { "Ref": "MySNSTopic" }
      }
    }
  }
}

This JSON is an AWS CloudFormation template that creates an SNS topic named example-topic. It also creates a subscription that sends emails to [e-mail] when messages are published to the topic.

MySNSTopic: Defines the SNS topic resource.

MySubscription: Defines the subscription resource linking the topic to an email endpoint.

Commands

This command creates a new SNS topic named 'example-topic' where messages can be published.

Terminal

aws sns create-topic --name example-topic

Expected Output

{"TopicArn":"arn:aws:sns:us-east-1:123456789012:example-topic"}

→

--name - Specifies the name of the SNS topic to create.

This command subscribes the email address '[e-mail]' to the SNS topic so it will receive messages.

Terminal

aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:example-topic --protocol email --notification-endpoint [e-mail]

Expected Output

{"SubscriptionArn":"pending confirmation"}

→

--topic-arn - Specifies the ARN of the SNS topic to subscribe to.

→

--protocol - Defines the communication protocol, here 'email'.

→

--notification-endpoint - The email address that will receive notifications.

This command lists all subscriptions for the given SNS topic to verify the subscription was created.

Terminal

aws sns list-subscriptions-by-topic --topic-arn arn:aws:sns:us-east-1:123456789012:example-topic

Expected Output

{"Subscriptions":[{"SubscriptionArn":"pending confirmation","Owner":"123456789012","Protocol":"email","Endpoint":"[e-mail]","TopicArn":"arn:aws:sns:us-east-1:123456789012:example-topic"}]}

→

--topic-arn - Specifies the SNS topic to list subscriptions for.

Key Concept

If you remember nothing else from this pattern, remember: SNS topics let you send messages to many subscribers easily by creating a topic and adding subscriptions.

Common Mistakes

Not confirming the subscription email after subscribing.

The subscription stays in 'pending confirmation' and no messages are received.

Check your email and click the confirmation link to activate the subscription.

Using the wrong ARN or topic name when subscribing.

The subscription command fails or subscribes to the wrong topic.

Copy the exact TopicArn from the create-topic output and use it in the subscribe command.

Trying to subscribe with an unsupported protocol or invalid endpoint.

Subscription creation fails or messages are not delivered.

Use supported protocols like email, sms, http, https, and valid endpoints.

Summary

Create an SNS topic to group messages for multiple receivers.

Subscribe endpoints like email addresses to the topic to receive messages.

Verify subscriptions and confirm them to start receiving notifications.

Practice

1. What is the main purpose of an SNS topic in AWS?

easy

A. To store files and documents securely

B. To act as a message hub where messages are sent and distributed

C. To run virtual servers in the cloud

D. To manage user permissions and access

Solution

1. Step 1: Understand SNS topic role

   An SNS topic is like a message board where messages are posted for others to receive.

2. Step 2: Compare options to SNS function

   Only To act as a message hub where messages are sent and distributed describes a message hub, which matches SNS topic's purpose.

3. Final Answer:

   To act as a message hub where messages are sent and distributed -> Option B

4. Quick Check:

   SNS topic = message hub [OK]

Hint: SNS topics distribute messages to subscribers [OK]

Common Mistakes:

• Confusing SNS topics with storage services
• Thinking SNS manages servers
• Mixing SNS with user access control

2. Which of the following is the correct way to subscribe an email endpoint to an SNS topic using AWS CLI?

easy

A. aws sns subscribe --subscription-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol email --notification-endpoint [e-mail]

B. aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --notification-endpoint [e-mail]

C. aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol email --notification-endpoint [e-mail]

D. aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol email --endpoint [e-mail]

Solution

1. Step 1: Review AWS CLI subscribe syntax

   The correct command uses 'aws sns subscribe' with '--topic-arn', '--protocol', and '--endpoint' parameters.

2. Step 2: Check option correctness

   The correct command is 'aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol email --endpoint [e-mail]'. Distractors use incorrect parameters like --notification-endpoint, miss --protocol, or use --subscription-arn.

3. Final Answer:

   aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol email --endpoint [e-mail] -> Option D

4. Quick Check:

   Correct CLI syntax = aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol email --endpoint [e-mail] [OK]

Hint: Use --protocol and --endpoint with aws sns subscribe [OK]

Common Mistakes:

• Using wrong parameter names like --notification-endpoint instead of --endpoint
• Missing the --protocol flag
• Confusing topic ARN with subscription ARN

3. Given this Python code using boto3, what will be the output if the subscription is successful?

import boto3
sns = boto3.client('sns')
response = sns.subscribe(
    TopicArn='arn:aws:sns:us-east-1:123456789012:MyTopic',
    Protocol='email',
    Endpoint='[e-mail]'
)
print(response['SubscriptionArn'])

medium

A. 'pending confirmation' string indicating subscription needs confirmation

B. An error message about missing permissions

C. The ARN of the SNS topic

D. The ARN of the new subscription if confirmed

Solution

1. Step 1: Understand SNS email subscription behavior

   Email subscriptions require the user to confirm by clicking a link. Until then, the SubscriptionArn is 'pending confirmation'.

2. Step 2: Analyze the printed output

   The code prints response['SubscriptionArn'], which will be 'pending confirmation' until user confirms.

3. Final Answer:

   'pending confirmation' string indicating subscription needs confirmation -> Option A

4. Quick Check:

   Email subscription = pending confirmation [OK]

Hint: Email subscriptions show 'pending confirmation' until user confirms [OK]

Common Mistakes:

• Expecting immediate subscription ARN without confirmation
• Confusing topic ARN with subscription ARN
• Assuming no confirmation needed for email protocol

4. You wrote this AWS CLI command to subscribe an HTTP endpoint but get an error:

aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol http --notification-endpoint http://example.com/notify

What is the most likely cause of the error?

medium

A. The HTTP endpoint URL must use HTTPS, not HTTP

B. The topic ARN is invalid

C. The protocol should be 'https' instead of 'http'

D. The notification endpoint URL is missing a trailing slash

Solution

1. Step 1: Check protocol requirements for HTTP endpoints

   AWS SNS requires HTTP endpoints to use HTTPS for security; HTTP URLs cause errors.

2. Step 2: Validate the given URL and protocol

   The URL uses 'http://' which is not allowed; it must be 'https://'.

3. Final Answer:

   The HTTP endpoint URL must use HTTPS, not HTTP -> Option A

4. Quick Check:

   HTTP endpoints require HTTPS URL [OK]

Hint: Use HTTPS URLs for HTTP/HTTPS SNS subscriptions [OK]

Common Mistakes:

• Assuming HTTP URLs are accepted
• Thinking trailing slash matters
• Confusing protocol parameter values

5. You want to send a notification to multiple endpoints: an email, an SMS number, and a Lambda function. How should you configure SNS to achieve this?

hard

A. Send messages directly to each endpoint without using SNS topics

B. Create separate SNS topics for each endpoint type and publish messages to all

C. Create one SNS topic and subscribe all three endpoints to it

D. Use only email and SMS subscriptions; Lambda cannot subscribe to SNS

Solution

1. Step 1: Understand SNS subscription flexibility

   An SNS topic can have multiple subscriptions of different protocols (email, SMS, Lambda).

2. Step 2: Choose the simplest and best practice approach

   Using one topic with multiple subscriptions is efficient and standard practice.

3. Final Answer:

   Create one SNS topic and subscribe all three endpoints to it -> Option C

4. Quick Check:

   One topic, multiple subscriptions = Create one SNS topic and subscribe all three endpoints to it [OK]

Hint: One SNS topic can have many different subscriptions [OK]

Common Mistakes:

• Thinking Lambda cannot subscribe to SNS
• Creating multiple topics unnecessarily
• Sending messages directly without SNS