SNS and SQS integration pattern (fan-out) in AWS - Step-by-Step Execution

Process Flow - SNS and SQS integration pattern (fan-out)

Message published to SNS topic

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SNS topic receives message

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SNS fans out message to multiple SQS queues

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SQS Queue 1

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Consumers read messages independently

A message is sent to an SNS topic, which then copies and sends it to multiple SQS queues. Each queue can be processed separately by different consumers.

Execution Sample

AWS

Publish message to SNS topic
SNS fans out to SQS queues
Each SQS queue receives the message
Consumers poll SQS queues
Process messages independently

This shows how a single message sent to SNS is delivered to multiple SQS queues for parallel processing.

Process Table

Step	Action	SNS Topic State	SQS Queue 1 State	SQS Queue 2 State	SQS Queue 3 State	Consumer Processing
1	Message published to SNS topic	Message received	Empty	Empty	Empty	No processing yet
2	SNS fans out message to SQS queues	Messages delivered	Message received	Message received	Message received	No processing yet
3	Consumer 1 polls SQS Queue 1	Messages delivered	Message in flight	Message received	Message received	Consumer 1 processing message
4	Consumer 2 polls SQS Queue 2	Messages delivered	Message in flight	Message in flight	Message received	Consumer 1 and 2 processing messages
5	Consumer 3 polls SQS Queue 3	Messages delivered	Message in flight	Message in flight	Message in flight	All consumers processing messages
6	Consumers delete messages after processing	Messages delivered	Empty	Empty	Empty	All consumers done
7	No more messages	Empty	Empty	Empty	Empty	No processing
Exit	All messages processed and queues empty	No messages	No messages	No messages	No messages	Idle

💡 All messages processed and deleted from queues, SNS topic has no pending messages

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
SNS Topic Messages	0	1	0	0	0	0	0	0
SQS Queue 1 Messages	0	0	1	0 (in flight)	0 (in flight)	0 (in flight)	0	0
SQS Queue 2 Messages	0	0	1	1 (in flight)	0 (in flight)	0 (in flight)	0	0
SQS Queue 3 Messages	0	0	1	1	1 (in flight)	0 (in flight)	0	0
Consumers Processing	None	None	None	Consumer 1	Consumer 1 & 2	All 3	None	None

Key Moments - 3 Insights

Why does each SQS queue get its own copy of the message?

Because SNS fans out the message to all subscribed queues independently, as shown in execution_table step 2 where all queues receive the message.

What happens if one consumer processes its message slower than others?

That queue's message stays 'in flight' until processed and deleted, while other queues can process their messages independently, as seen in steps 3 to 5.

Does deleting a message from one SQS queue remove it from others?

No, each SQS queue holds its own copy. Deleting from one queue does not affect messages in other queues, as shown in step 6.

Visual Quiz - 3 Questions

Look at the execution_table at step 2. What is the state of SQS Queue 2?

A Empty

B Message received

C Message in flight

D Message deleted

💡 Hint

Check the 'SQS Queue 2 State' column at step 2 in the execution_table.

At which step do all consumers start processing their messages simultaneously?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Consumer Processing' column to see when all consumers are active.

If the message is deleted from SQS Queue 1 at step 6, what happens to the message in SQS Queue 3?

A It remains until processed

B It moves to SQS Queue 1

C It is also deleted

D It is duplicated

💡 Hint

Refer to the key moment about message deletion and independent queues.

Concept Snapshot

SNS and SQS fan-out pattern:
- Publish message to SNS topic
- SNS sends copies to all subscribed SQS queues
- Each SQS queue holds its own copy
- Consumers poll and process messages independently
- Deleting from one queue does not affect others

Full Transcript

This visual execution shows how a message published to an SNS topic is copied to multiple SQS queues. Each queue receives the message independently and holds it until a consumer processes and deletes it. Consumers can work in parallel without affecting each other. SNS delivers the message asynchronously to all subscribed queues. This pattern enables scalable, parallel processing of the same message by multiple consumers.