SQS Message Visibility Timeout | Overview & Hands-On.

SQS Message Visibility Timeout - Overview & Hands-On.

Scope:

• Intro,
• The concept,
• Importance of Amazon SQS Message Visibility Timeout,
• Key Points,
• Sample Workflow,
• Changing the Visibility Timeout,
• Common Pitfalls (limitations),
• Best Practices,
• Project: Hands-On,

Intro:

SQS Message Visibility Timeout is a crucial feature in Amazon SQS that controls how long a message stays invisible to other consumers after being retrieved from the queue.

The concept:

• When a consumer retrieves (polls) a message from an SQS queue using ReceiveMessage, the message does not get deleted—it's just marked as invisible for a certain period, called the visibility timeout. This gives the consumer time to process and delete the message.
• By default, the “message visibility timeout” is 30 seconds. That means the message has 30 seconds to be processed. When the message visibility timeout is over, the message becomes “visible” in the SQS(simple queue service).
• If the message isn't deleted before the timeout expires, it becomes visible again and can be retried or redelivered to the same or another consumer.
• If a message is not processed within the visibility timeout, it will be processed twice.  A consumer may make API call for ChangeMessageVisibility to get more time.
• If the visibility timeout is high (in hours), and consumer crashes, re-processing would take time.
• If visibility timeout is very low (say in seconds),  duplicate messages will appear.

 Importance of Amazon SQS Message Visibility Timeout:

• Prevents duplicate processing while a message is being worked on.
• Ensures reliability: if a consumer fails or crashes before processing is complete, the message will reappear for someone else to handle.
• Helps in fault-tolerant and at-least-once message delivery.

Key Points.

Feature	Description
Default	30 seconds
Range	0 seconds to 12 hours
Change per message	Yes, using ChangeMessageVisibility
Queue-level setting	Yes, set during queue creation or updated later
Message reprocessing	If a message isn't deleted within the timeout, it will reappear for reprocessing

Sample Workflow.

1. A message is sent to an SQS queue.
2. A consumer receives the message → SQS sets it as invisible (default: 30 seconds).
3. The consumer processes the message.
4. If successful → the consumer calls DeleteMessage → message is removed.
5. If not → after timeout expires → the message becomes visible again for reprocessing.

 Changing the Visibility Timeout.

• Per-queue (default for all messages):
  Use AWS Console, CLI, or SDK to set VisibilityTimeout when creating or updating a queue.
• Per-message (useful for long-running jobs):
  Use the ChangeMessageVisibility API to increase the timeout dynamically.

 Common Pitfalls(limitations).

• Short visibility timeout: If your message processing takes longer than the timeout, it may get redelivered and processed multiple times.
• Not deleting messages: Forgetting to delete processed messages leads to them being reprocessed after timeout.

twtech Best Practices

• Set a visibility timeout slightly longer than the average processing time.
• Use dead-letter queues (DLQs) for messages that exceed the max receive count.
• Adjust visibility dynamically for long or variable processing times.

Project: Hands-on

• How twtech configures visibility timeout on its SQS(simple queue service).
• Go to SQS(simple queue service) UI: to send a message.

• Send and receive a message: Hello twtech family

• Poll for messages:

From:

To:

• twtech may change (edit) the default visibility timeout for SQS (simple queue service)

From: 30Sec

To: 120Sec 

• Remembeer to save changes.

Insights:

• The beauty of this configuration can be viewed by opening two UI for sending and receiving messages.