Decoupling

Question 1

What is the advantage of loosely coupled system?

Answer 1

If any one instance fails, the application will still work or be able to recover

Question 2

Should you tightly couple systems?

Answer 2

No you should never tightly couple systems e.g. instances should not talk directly to another

Question 3

At what level of your app should it be loosely coupled?

Answer 3

At every level should be loosely coupled

Question 4

What processing type does SQS allow?

Answer 4

Allows asynchrous processing

Question 5

What is the SQS max message size?

Answer 5

256KB per message

Question 6

What is encrypted by default for SQS? What is not?

Answer 6

Encrypted default for in transit but not default for at-rest

Question 7

Between short polling and long polling, what should you focus on in the exam? Which is default?

Answer 7

Focus on long polling. Short polling is default

Question 8

What is the min and max message retention period? Default?

Answer 8

Min Retention is 1 minute
Max Retention is 14 days
Default 4 days

Question 9

What is Queue Depth and what is used for?

Answer 9

Queue Depth is the amount of messages backed up in the queue and used for kicking off auto scaling consumers

Question 10

What is delivery delay? The default? The max?

Answer 10

The amount of time new messages remain invisible to consumers of the queue. Default is 0 minutes. Max is 15 minutes

Question 11

What is visibility timeout? The default? The max/min?

Answer 11

Visibility timeout is the time period where a message is not visible to consumers for processing/consumption. A consumer has this amount of time to process the message before it goes back onto the queue.

Default is 30 seconds
Max is 12 hours
Min is 0 seconds

Question 12

What should you setup along with Dead Letter Queues?

Answer 12

Cloud Watch Alarms on queue depth to let you know things are backed up

Question 13

What 2 things should you consider if there is a question about problems with a SQS queue?

Answer 13

1. Dead Letter Queue

2. Visibility Timeout

Question 14

What other service can you use ideally with DLQ?

Answer 14

You can send failed SNS messages to a DLQ

Question 15

What are Dead Letter Queues?

Answer 15

SQS Queues where failed/rejected messages go after a certain amount of retries in the main SQS queue

Question 16

What are the ordering characteristics of a Standard SQS?

Answer 16

Ordering is best try and not guaranteed

Question 17

What are the ordering characteristics of a FIFO SQS?

Answer 17

Order is guranteed for FIFO

Question 18

What are the delivery duplication characteristics of a Standard SQS?

Answer 18

Delivery is at least once and could be duplicated

Question 19

What are the delivery duplication characteristics of a FIFO SQS?

Answer 19

Delivery will never be duplicated

Question 20

What 2 reasons would Standard SQS be better over FIFO?

Answer 20

1. Less Costly

2. Has higher throughput, while FIFO has a cap 300 tx per second

Question 21

What are the subscribers possible for SNS?

Answer 21

SQS,HTTP/HTTPS, Lambda, email, SMS, Kinesis Firehose, SMS

Question 22

Does SNS have retries for pushing to subscribers?

Answer 22

Yes, only for HTTP/HTTPS

Question 23

What is the max message size for SNS?

Answer 23

256 KB

Question 24

What are the 2 types of SNS? What is the difference?

Answer 24

1. FIFO
   2.Standard
   FIFO only supports SQS as subscribers

Question 25

What is the encryption for SNS? Defaults?

Answer 25

1. Default encrypted in transit

2. At Rest needs to be turned on

Question 26

What is the best friend to SNS?

Answer 26

CloudWatch and CloudWatch Alarms to delivery alerts

Question 27

What should you select for marketing emails? What will the exam try to trick you with emails?

Answer 27

SES is only for marketing emails. Email notifications pick SNS from Cloudwatch

Question 28

What should you select for marketing emails? What will the exam try to trick you with emails?

Answer 28

SES is only for marketing emails. Email notifications pick SNS from Cloudwatch

Question 29

What is the policy situation with SNS?

Answer 29

Access Policy can be put on a Topic to control who can publish to the topic

Question 30

How would SQS, retries and SNS work?

Answer 30

Send failed notifications in SNS to DLQ as SNS doesnt retry except or HTTP(S)

Question 31

When should you use API Gateway?

Answer 31

When exam mentions API, a safe front door is needed to interact into AWS from external

Question 32

what are 4 whys to use API Gateway?

Answer 32

1. It allows you to use WAF,
2. rate limiting against DDOS,
3. gets away from hard coded credentials,
4. supports versioned apis by staging

Question 33

What should you think about when exam mentions syncrhouns? mentions async?

Answer 33

1. sync use ELB

2. async use SQS

Question 34

What is SNS fan out?

Answer 34

ALlows you to send the same message ot multiple subcribes at the same time

Question 35

What is SQS Long polling? Why use this?

Answer 35

Where the consumer connects to SQS and waits for a certain amount of seconds for a message before closing the connection.
This will save money by reducing network traffic

Question 36

What is SQS short polling?

Answer 36

Where the consumer connects to SQS to check for messages and if there are none immediately closes the connection then tries again.

Question 37

What does a consumer need to do within the visibility timeout period?

Answer 37

If consumer processes a message successfully, it must delete the message within this time period to prevent duplication.

If it fails but has only once delivery, it needs to delete the message in the queue within this period.