# SQS
#aws #cloud #serverless #microservices #decoupleing #queue
First-ever AWS service that was made publicly available. (Oldest service). Message Queue service enables web services applications to queue messages. Acts like a buffer between the components between different components and often used for decoupling different services. Can set up an Auto-scaling group to SQS which is a great practice. It can pick up messages using a “poll” and is mostly used for pull-based operations.
# Features
- Allow us to decouple the components of an application so that they are independent
- Pull based message store (Poll) (256 KB max size of the text in any format)
- Retrieve the messages using SQS API
- Text Data (XML, JSON and unformatted text)
- Guarantees that message will be processed at least once
- The default retention period is 4 days
- Max message retention time is 14 days
# Visibility Timeout
- Default is 30 seconds
- If a message isn’t processed within 30 seconds, the item will reappear
- You can increase the visibility Timeout.
- Max timeout is 12 hours
# Polling
Using S3 for large SQS message (256KB-2GB) (Amazon SQS Extended Client Library for Java, AWS SDK for java)
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Fully managed queing services that enables you to decouple a big complex architecture to a simpler one. It is primarily for Application integration.
pull based.
Messege size can be between 1 byte to 256 KB
Extended storage option is availabe on Java SDK which allows storage of message upto 2GB but will be required to be stored in S3.
Message retention by default is 4 days
from min of 60 seconds to max of 14 days
# Standard Queues
Allows nearly-unlimited number of transactions per second using best effort ordering which can maintain the deleviry order and this type of queue guarantees that a message will be delivered at least once. Which means more than one copy of message could be potentially delivered out of order.
# FIFO Queue
Supports multiple ordered message groups within a single queue and will be limited to 300 transactions per second. If batched 10 messages per operation (max), can support upto 3000 messages. Have all of the capabilities of a standard queue and eliminates more than once processing.
# Standard vs FIFO
# Dead Letter Queue
To handle message failure, A DLQ will set aside the message which was not processed correctly. It can be either Standard Queues or FIFO Queue which will be specified as a DLQ to an existing SQS queue. SQS Delay Queue postpones delivery of new messages (makes them invisible)(0s-900s).
It only affects standard queues but it will affect the whole FIFO Queue. (e.g. for confirming the order in E-commerce).
# Delay Queue
A message could be hidden when created in SQS for some time.
# Visibility Timeout
To prevent another app from reading a message which is already being processed by another app. This help
# Polling
Short Polling vs Long Polling
