Amazon SQS

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

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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.

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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

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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

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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

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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

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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.

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Important Terms to know

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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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