AWS Applications

Question 1

What is SQS?

Answer 1

SQS is a web service that gives you access to a messaging queue that can be used to store messages while waiting for a computer to process them.

Question 2

What does SQS enable?

Answer 2

SQS enables the ‘decoupling’ of the components of an application so that they can run independently and easing message management between components.

Question 3

What are the two types of SQS queue?

Answer 3

The two types of SQS queue are:

• Standard queues
• FIFO queues

Question 4

How does SQS act as a buffer?

Answer 4

SQS provides a buffer between the component producing data and the component receiving the data.

The queue resolves issues that arise if the producer is producing work faster than the consumer can process it, or if the producer or consumer are only intermittently connected to the network.

Question 5

What do SQS Standard Queues provide in terms of transactions per second and delivery guarantees?

Answer 5

A standard queue lets you have a nearly unlimited number of transactions per second and guarantee that a message is delivered at least once.

Question 6

What is a potential downside to standard SQS queues?

Answer 6

A potential downside to standard SQS queues is that more than one copy of a message may be delivered out of order

Question 7

What is a benefit of standard SQS queues?

Answer 7

Standard queues provide best-effort ordering which ensures messages are generally delivered in the same order as they are sent

Question 8

What are FIFO queues?

Answer 8

FIFO ensures first in first out and exactly-once processing.

Question 9

What type of queues support message groups?

Answer 9

FIFO queues support message groups that allow multiple ordered message groups within a single queue

Question 10

What is the transaction per second limit for FIFO queues?

Answer 10

FIFO queues are limited to 300 transactions per second

Question 11

Is SQS pull or push based?

Answer 11

SQS is pull based

Question 12

What are the size of SQS messages?

Answer 12

SQS message size is 256kb

Question 13

What are the retention periods for SQS messages?

Answer 13

Messages can be kept in the queue for 1 minute to 14 days, the default is 4 days

Question 14

What is an SQS Visibility Timeout?

Answer 14

A visibility timeout is the amount of time that the message is invisible in the SQS queue after a reader picks up the message.

If the job is not processed within that time, the message will become visible again and another reader will process it which could result in the same message being delivered twice.

Question 15

What is the visibility timeout maximum?

Answer 15

The visibility timeout maximum is 12 hours

Question 16

What does SQS guarantee with regards message delivery?

Answer 16

Standard queues provide at-least-once delivery, which means that each message is delivered at least once.

FIFO queues provide exactly-once processing, which means that each message is delivered once and remains available until a consumer processes it and deletes it.

Question 17

Do Standard SQS message queues preserve either message order or guarantee that they are delivered only once?

Answer 17

The Standard SQS message queue does not preserve message order nor guarantee messages are delivered only once - these are features of a FIFO message queue

Question 18

When does duplicate messaging occur?

Answer 18

Duplicate messages occur when a consumer does not complete its message processing and the visibility timeout of the message expires, making it visible for another consumer to obtain.

Increasing the visibility timeout to enable the consumer processing to complete, will prevent duplicate messages.

Question 19

Can you convert a standard queue into a FIFO queue?

Answer 19

You can’t convert an existing standard queue into a FIFO queue. To make the move, you must either create a new FIFO queue for your application or delete your existing standard queue and recreate it as a FIFO queue.