SNS topics and subscriptions in AWS - Step-by-Step Execution

Process Flow - SNS topics and subscriptions

Create SNS Topic

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Create Subscription

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Publish Message to Topic

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SNS Delivers Message to Subscribers

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Subscribers Receive Message

This flow shows how an SNS topic is created, subscriptions are added, messages are published, and then delivered to subscribers.

Execution Sample

AWS

aws sns create-topic --name MyTopic
aws sns subscribe --topic-arn <topic-arn> --protocol email --notification-endpoint [e-mail]
aws sns publish --topic-arn <topic-arn> --message "Hello Subscribers!"

This code creates an SNS topic, subscribes an email endpoint, and publishes a message to the topic.

Process Table

Step	Action	Input	Output	State Change
1	Create SNS Topic	Name=MyTopic	TopicArn=arn:aws:sns:region:account:MyTopic	Topic created with ARN
2	Subscribe to Topic	TopicArn=arn:aws:sns:region:account:MyTopic, Protocol=email, Endpoint=[e-mail]	SubscriptionArn=arn:aws:sns:region:account:MyTopic:sub-id	Subscription added to topic
3	Publish Message	TopicArn=arn:aws:sns:region:account:MyTopic, Message="Hello Subscribers!"	MessageId=msg-id	Message queued for delivery
4	Deliver Message	MessageId=msg-id	Success	Message sent to subscriber endpoint
5	Subscriber Receives Message	Email inbox	Message content: "Hello Subscribers!"	Subscriber notified
6	End	No further actions	N/A	Process complete

💡 All subscribers have received the published message, process ends.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
TopicArn	None	arn:aws:sns:region:account:MyTopic	arn:aws:sns:region:account:MyTopic	arn:aws:sns:region:account:MyTopic	arn:aws:sns:region:account:MyTopic	arn:aws:sns:region:account:MyTopic
SubscriptionArn	None	None	arn:aws:sns:region:account:MyTopic:sub-id	arn:aws:sns:region:account:MyTopic:sub-id	arn:aws:sns:region:account:MyTopic:sub-id	arn:aws:sns:region:account:MyTopic:sub-id
MessageId	None	None	None	msg-id	msg-id	msg-id
MessageDelivered	False	False	False	False	True	True

Key Moments - 3 Insights

Why do we need to create a subscription after creating a topic?

Creating a topic only sets up the channel. Subscriptions tell SNS where to send messages. See execution_table step 2 where subscription is added after topic creation.

What happens if no subscriptions exist when a message is published?

SNS accepts the message but has no endpoints to deliver to, so no delivery occurs. This is implied by the need for subscriptions in step 2 before publishing in step 3.

Does publishing a message guarantee delivery to subscribers immediately?

Publishing queues the message for delivery (step 3), but actual delivery happens next (step 4). Delivery depends on subscriber availability.

Visual Quiz - 3 Questions

Look at the execution table, what is the TopicArn value after step 1?

A arn:aws:sns:region:account:MyTopic

B None

C arn:aws:sns:region:account:MyTopic:sub-id

D msg-id

💡 Hint

Check the 'TopicArn' row in variable_tracker after step 1.

At which step does the message get queued for delivery?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' and 'State Change' columns in execution_table for message publishing.

If no subscriptions were created, what would happen at step 4?

A Message would be delivered to subscribers

B SNS would throw an error and stop

C Message would be queued but not delivered

D Message would be deleted immediately

💡 Hint

Refer to key_moments about publishing without subscriptions.

Concept Snapshot

SNS Topics and Subscriptions:
- Create a topic to act as a message channel.
- Add subscriptions to specify where messages go.
- Publish messages to the topic.
- SNS delivers messages to all subscribers.
- Subscribers receive notifications asynchronously.

Full Transcript

This visual execution shows how AWS SNS topics and subscriptions work. First, a topic is created which acts like a message channel. Then, subscriptions are added to tell SNS where to send messages, such as an email address. When a message is published to the topic, SNS queues it and then delivers it to all subscribed endpoints. The subscriber finally receives the message. Variables like TopicArn, SubscriptionArn, and MessageId track the state through each step. Key moments clarify why subscriptions are needed and how delivery works. The quiz tests understanding of these steps and states.