SQS

Question 1

what is SQS

Answer 1

SQS is a way to decouple infrastructure
pull based
messages in 256 KBB size
can be kept in a queue from 1 minute-14 days with a default retention period of 4 days
standard SQS/Fifo SQS
Standard SQS might duplicate and cannot guarentee order
FIFO guarentes order and only once and 3,000 tps per second

Question 2

Visibility Timeout

Answer 2

message is invisible after the reader picks up that message. Provided the job is processed before the visibilty expires then the message will be deleted from the queue else the message will become visible again for another reader to process the same. This could result in processing the message twice

Question 3

Visibility Timeout max

Answer 3

Visibbility timeout maximum is 12 hrs

Question 4

Polling

Answer 4

Polling is a way to retrieve messages
Long polling does not return a response until a message arrives in the message queue or the long poll times out
Short polling returns immediately even if the message queue being polled is empty.

Question 5

SQS Vs SWF

Answer 5

SQS max retention period is 14 days. SWF workflow executions can last up to 1 year
SWF presenst a task oriented API
SQS message oriented API
SWF ensures that task is assigned only once.. with SQA you need to handle duplicated messages and may also need to ensure that message is processed only once.

Amazon SWF keeps track of all the tasks and events on an application. with SQS YOU NEED TO implement your own application level tracking especially if your applciations uses multiple queues

Question 6

SWF workflow Actors

Answer 6

Workflow Starters - Application that initiate the workflow
Deciders - controls the flow of activity tasks in workflow execution
Activity Workers - Carry out activity tasks

In SWF domain refer to “Collection of related workflows”

AWS SWF does not retrict the use of specific programming languages as it supports hTTP based API and you can implement API however