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Amazon SQS

Updated: Jun 21, 2020

This article talks about Amazon SQS, its features and its types in a summarized way.


What is Amazon SQS?

Amazon Simple Queue Service (SQS) is a fully managed queue service by Amazon web services. It simply stores and sends messages between software components. SQS enables to decouple micro-services, distributed and server-less applications. It is a scale-able and cost-effective service. There is no upfront cost and one can pay as per usage.

The below illustration shows that a queue having multiple messages being sent from one application component to other.


What are the features of Amazon SQS?

Following are the typical features of Amazon SQS service.

  • Unlimited messages and queues allowed

  • Message size accepted upto 256 KB

  • Batch messages upto 10 messages or 256 KB size in total accepted

  • Messages retained upto 14 days in the queue

  • Simultaneous send and read messages

  • Message locking option available

  • Queue sharing allowed securely with other AWS accounts

  • Encryption (SSE) option available with AWS KMS

  • Dead Letter Queue available for messages not processed successfully


What are the type of queues in Amazon SQS?

There following are the 2 types of queues for delivering messages.

  • Standard Queue

  • FIFO Queue

However, there is also another queue for storing messages that are not processed successfully.

  • Dead Letter Queue


Standard Queue

The below illustration shows how a standard queue delivers messages across components.

  • Messages are delivered at least once

  • Chances of duplication of messages. This means there may be rare chances that a message may be delivered more than once.

  • Order of messages not guaranteed


FIFO Queue

The below illustration shows how a FIFO queue delivers messages across components

  • Messages are delivered as first in-first out order

  • Messages are delivered only once

  • No duplicates delivered


Dead Letter Queue (DLQ)

As mentioned above, this queue is for messages that are not processed successfully. These messages are move to this queue (DLQ) for investigation and analysis. A message can be moved to a standard dead letter queue only when its parent queue is also standard queue and its the same with FIFO queue as well.


Important Terms to know


Message Visibility Timeout

When a message is received in the queue and is being processed by a component, Amazon SQS prevents or hides this message from other consumers processing it by setting a visibility timeout. This means the message will not be visible to other consumers until the visibility timeout duration. This duration can be set from 0 secs to 12 hours per message. The default is set to 30 secs per message.

Message Short Polling

  • Receive message request queries only a subset of servers to find the messages.

  • Response is sent immediately even if there is no messages found.

Message Long Polling

  • Receive message request queries all the servers to find the messages.

  • Response is sent only after it collects at-least one available message.

  • If there are no messages in the queue, it waits until the polling wait time expires.


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