SQS

• Simple Queue Service
• SQS is pull based. Compute services (EC2, Lambda) polls and pull the messages. Use SQS for decouple architecture
• Standard queue – Guarantee delivery once, can get delivered more than once, ordering not guaranteed
• FIFO queue – No duplicates, guarantee delivery order, dups deleted within 5 mins
• Short polling – Polls even when no message in queue. Used only when one thread polls multiple queue
• Long polling  – Preferred; to save on unwanted polling. Polls only when a message arrives in the queue
• Visibility time – Once message is read it is made invisible to others (default 30 secs)
• Delay seconds – Time message is hidden when it is first added to the queue
• Reading program (Lambda, EC2) must delete the message from queue after processing

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