Chpater 11 Refactor to Microservices

Question 1

Explain AWS SQS at a high level

Answer 1

Simple Queue Service. It temporarily stores messages from a provider while it waits for a message producer to process the message.

Messages are stored passively (no notification)

Question 2

What are the limits to the number of producers and consumers for SQS?

Answer 2

There are no limits. SQS is a distributed cluster of servers.

Question 3

List states of SQS message

Answer 3

1. Sent to queue by a producer
2. Received from queue from a consumer
3. Deleted from queue

Question 4

What is an ‘in-flight’ state for an SQS message?

Answer 4

When a message is b/t states of received and deleted. There are a finite number of in-flight messages that can be processed.

Question 5

What is ‘Long-Polling’ in SQS and how do you implement it?

Answer 5

Method to reduce operational cost of SQS by eliminating empty responses.

Achieved by setting longer time intervals for the ‘ReceiveMessage’ action (max is 20 seconds, min is 1 second)

Question 6

What is the ‘VisibilityTimeout’?

Answer 6

SQS actions which is the duration (in seconds) that the received messages are hidden from subsequent retrieve requests after being retrieved by a ‘ReceiveMessage’ request.

Question 7

If you find yourself setting the VisibilityTimeout action in SQS to longer than 12 hours, what should you consider doing instead?

Answer 7

Use AWS Step Functions

Question 8

What is a ‘Dead Letter Queue’?

Answer 8

A queue/dump where failed messages are stored. For example, a user order item with a deleted product ID. Associated message can be sent to the dead letter queue.

Useful for:

• configuring alarm for any messages received in DLQ
• analyze contents of problematic messages
• determineif you gave consumer sufficient processing time
• DLQ must be FIFO when used w/ SQS FIFO queue
• DLQ must be standard when used w/ SQS Standard Queue

Question 9

SQS Standard Queues ensure scalability and throughput by having what two tradeoffs?

Answer 9

• order is not guaranteed

- messages can appear twice

Question 10

What is alternative to SQS Standard Queues?

Answer 10

SQS FIFO queues:

• provide ordered messages
• delete any duplicates that appear in queue

Question 11

With Kinesis Data Streams, how/when are messages/records deleted?

Answer 11

Via a retention interval expiration, which you configure

Question 12

How to support high throughput in Kinesis Data Streams?

Answer 12

Increase number of shards in Kinesis Data Stream system

Question 13

Difference b/t Kinesis Firehose and Kinesis Data Streams?

Answer 13

Higher level. Firehose does not require you to write a consumer application.

Also Firehose handles dynamic scaling of underlying shards and automatically delivers data to services like S3, Redshift, etc.

Question 14

AWS Kinesis Data Analytics

Answer 14

Allows you to process and analyze streaming data with SQL. Good for performing time series analytics, feed real time dashboards, create real time metrics.

Question 15

For Kinesis Streams, what is data made of?

Answer 15

1. ‘data blobs’ of up to 1MB attached to a…
2. ‘record key’ (metadata to tell which shard to go to)
3. sequence #

Question 16

DynamoDB Streams

Answer 16

Event pool which receives dynamoDB events from CRUD actions. Often integrated with Lambda via ‘triggers’

Question 17

At any given time, each partition in an Amazon DynamoDB table maps to a single ______ which captures all updates to that partition.

Answer 17

shard

Question 18

What is connector b/t IOT devices and AWS Services?

Answer 18

Rules Engine

*no retry or delivery guarantees for messages

Question 19

What protocols can devices use to communicate w/ AWS IOT?

Answer 19

1. MQTT Message Queuing Telemetry Transport

2. HTTP

Question 20

AWS IOT Message Broker

Answer 20

pub/sub broker service for messages to and from IOT devices. No cross region / cross account capabilities

Question 21

How to represent and communicate with offline device in AWS?

Answer 21

via AWS IOT device shadow

Question 22

What is AWS’s managed message broker service which is compatible with many popular message brokers?

Answer 22

Amazon MQ

Question 23

With Step functions, built in 1. _____, 2.____, and 3.____ capabilities deal with errors and exceptions automatically

Answer 23

1. try/catch
2. retry
3. rollback

Question 24

Step functions implement basic primitives such as ____, ___, and ___.

Answer 24

branching, parallel execution, timeouts

Question 25

What is language used to control step functions?

Answer 25

Amazon States Language

Question 26

List all functions for step functions

Answer 26

Task state: Performs work in your state machine

Choice state: Makes a choice between branches of execution

Fail or Succeed state: Stops an execution with a failure or success

Pass state: Passes inputs to outputs or inject corrected data

Wait state: Provides a delay for a certain amount of time or until a specified time/date

Parallel state: Begins parallel branches of execution

Question 27

If a parallel branch in a step function fails, can you stop a running Lambda function?

Answer 27

no

Question 28

How to stop long running activities in parallelized step function?

Answer 28

check heartbeat to detect whether step functions has stopped its branch

Question 29

In step functions each step defines either a ____ or a ____.

Answer 29

1. next state

2. end state

Question 30

In the Amazon States Language, three components filter and control the flow of JSON from state to state: 1.____, 2._____, and 3._____.

Answer 30

1. InputPath
2. OutputPath
3. ResultPath

Question 31

Size of SQS message?

Answer 31

256kb

Question 32

Size of SNS message?

Answer 32

256kb

Question 33

You have an Amazon Kinesis data stream with one shard and one producer. How many consumer applications can you consume from the stream?

Answer 33

Limitless number of consumers as long as all consumers consume fewer than 2 MB and five transactions per second