Decoupling and Messaging

Question 1

Loose Coupling

Answer 1

• almost always better
• you never want one EC2 instance talking to another instance -> you want some kind of managed service acting as the go between

Question 2

SQS

Answer 2

Simple queue service

• fully managed
• poll-based messaging

Question 3

Simple Notification Service

Answer 3

• to deliver notifications to an endpoint

- to deliver text messages or emails

Question 4

API Gateway

Answer 4

• a fully managed service that makes it easy for developers to create, publish, maintain, monitor and secure APIs at any scale

Question 5

SQS Producer

Answer 5

• writes the message to the queue

Question 6

SQS Consumer

Answer 6

• pickups up the message when they are ready

Question 7

SQS Setting - Delivery Delay

Answer 7

• default: 0
• up to 15 min
• queue holds the message

Question 8

SQS Setting - Message Size

Answer 8

• up to 256 KB of text in any format

Question 9

SQS & SNS Setting - Encryption

Answer 9

• default: messages are encrypted in transit

- optional: can add encryption at rest

Question 10

SQS Setting - Message Retention*

Answer 10

• default: 4 days
• minimum: 1 minute
• maximum: 14 days

Question 11

SQS Setting - Long Polling*

Answer 11

API connects and waits (not selected by default)

- always choose long polling on the exam

Question 12

SQS Setting - Short Polling*

Answer 12

API connects and gets a message and disconnects

• lots of overhead
• costly
• don’t choose on exam

Question 13

SQS Setting - Queue Depth*

Answer 13

• this can be a trigger for autoscaling as the messages back up
• Cloud Watch tells EC2 instance to spin up to address the queue

Question 14

SQS Visibility Timeout*

Answer 14

• default timeout: 30 seconds
• once the consuming service attempts to download a message from the queue, it is locked for X seconds so no one else can see it
• If the backend fails to process the message and tell the queue it’s good, the message will re-appear in the queue
  Otherwise, if the backend sends back and all good message, then it is deleted from the queue

Question 15

Dead Letter Queues

Answer 15

• when a backend processes a message but the processing fails, it goes into the queue and gets stuck in a loop, instead, send it to a dead letter queue if they’ve reached the maximum # of re-tries
• same limits as regular SQS queue - max: 14 days

Question 16

What is the only way to take a message from a queue and temporarily set it aside?

Answer 16

Dead Letter Queue

Question 17

Why do you need to set an alarm on a Dead Letter Queue?

Answer 17

so you can catch it before something goes off the rails

Question 18

How to create a Dead Letter Queue

Answer 18

1) Need to create the dead letter queue before you create your main queue
2) then create the main queue and specify the dead letter queue and set the maximum receives = maximum retries

Question 19

Can SNS use dead letter queues?*

Answer 19

Yes, both SQS and SNS can use them

Question 20

Standard SQS Queues

Answer 20

• • SQS offers best effort ordering
• occasionally you might get a message twice
• nearly unlimited transactions per second
• cheaper

Question 21

FIFO Queues

Answer 21

• proper ordering
• there will be no duplicates
• 300 messages per second (slower)
• more costly
• queue name must end in .fifo
• requires: a message group ID and a message deduplication ID

Question 22

Fifo Message Group ID

Answer 22

• ensures messages are processed one by one

- all messages in the group are downloaded together

Question 23

SNS Push Based messaging

Answer 23

• you have to be ready at any point in time to receive a message
• proactively delivers messages to the endpoints subscribed to it

Question 24

SNS Setting - Subscribers*

Answer 24

• Kinesis Data Firehose
• SQS
• Lambda
• Email
• HTTP(s)
• SMS
• platform application endpoint

Question 25

SNS Setting - Message Size

Answer 25

256 KB in any format

Question 26

What is the only thing that can subscribe to an SNS FIFO?

Answer 26

SQS Queues, used for a fan out to multiple SQS queues

Question 27

SNS Setting - Access Policy

Answer 27

• a resource policy can be added to a topic, similar to S3

Question 28

SNS on exam

Answer 28

• not featured as heavily as SQS

- mostly for alerts and push-based

Question 29

SNS Fan out

Answer 29

When you subscribe multiple SQS queues to an SNS notification

Question 30

Why do you need an access policy on an SQS queue?

Answer 30

To allow SNS to send it notifications

Question 31

For questions about alerts, alarms, or pushing

Answer 31

pick SNS

Question 32

What is CloudWatch’s preferred mechanism for alerting?

Answer 32

SNS

Question 33

What does API Gateway help with?*

Answer 33

• helps you not bake credentials into code
• allows you to put a safe “front door” on your application
• allows outside world to talk to your resources in a way that is safe, controlled, monitored, and helps prevent abuse
• can restrict who, what, when and how it can be accessed
• can protect your endpoints by attaching a WAF
• can implement DDOS protection and rate-limit
• easy to use and build out calls that call other AWS services

Question 34

API Gateway stages*

Answer 34

different versions of the API, customizable