Chp 8: High Availability + Scalability --> ELF and ASG

Question 1

What is scalability? What are the types

Answer 1

• apps/system can handle greater loads by adapting

- types: horizontal/vertical

Question 2

What is vertical scalability?

Answer 2

• increasing the size

- scale up/down

Question 3

what is horizontal scalability

Answer 3

increase the # of instances

Question 4

high availability goes hand in hand with what?

Answer 4

horizontal scalability

Question 5

what does high availability mean?

Answer 5

• run app/system in at least 2 data centers (= AZ)

- can be active or passive

Question 6

What is a load balancer?

Answer 6

• servers that forward traffic to multiple servers downstream

Question 7

Why use a load balancer?

Answer 7

• spread load across multiple downstream instances
• expose a single point of access
• regular health checks
• provide SSL termination
• enforce stickiness with cookies
• high availability
• separate public traffic from private traffic
• AWS takes care of everything

Question 8

what are health checks?

Answer 8

is a clone on a port/route

Question 9

What are the types of load balancers?

Answer 9

1. classic
2. application
3. network
4. gateway

Question 10

classic load balancer/

Answer 10

http, https, tcp, ssl

Question 11

Application load balancer

Answer 11

• • http, https, websocket
• • good for microservices and container
• • port mapping

Question 12

ALB target groups

Answer 12

• ec2 instances
• ec2 tasks
• lambda function
• ip address

Question 13

How many groups can ALB be routed to?

Answer 13

many

Question 14

Health checks are at what level

Answer 14

target group level

Question 15

ALB– hostnames or IPs

Answer 15

fixed hostname. it doesnt see IP of the client

Question 16

ALB– how does it get the IP of the client?

Answer 16

used header x-forwarded port

Question 17

network load balancer

Answer 17

• • tcp, tls, udp
• • one static IP per AZ
• • supports assigning elastic IP

Question 18

NLB – target groups

Answer 18

• ec2 instances
• ip addresses (private ips)
• ALB

Question 19

Gateway load balancer

Answer 19

• operates at layer 3/network

- single entry/exit for all traffic

Question 20

Gateway load balancer’s target group

Answer 20

• EC2 instances

- IP addresses (private IP)

Question 21

What is a sticky session

Answer 21

the same client is always redirected to the same load balancer

Question 22

sticky sessions work for which type of load balancer

Answer 22

ALB and GLB

Question 23

what happens with cross zone load balancing?

Answer 23

each load balancer instance distributes evenly across all registered instances in all AZ

Question 24

what happens without cross-zone load balancing?

Answer 24

requests are distributed in the instances of the nodes of the ELB

Question 25

What is SSL? Whats the newer version?

Answer 25

- SSL encrypts connection | - TLS is the newer version

Question 26

Load balancers uses what kind of certs

Answer 26

x509

Question 27

Server Name Indication (SNI) -- Purpose

Answer 27

- SNI solves the problem of loading multiple SSL certs onto one web server - Only works for ALB + NLB

Question 28

What is an auto scaling group (ASG)

Answer 28

- scale out to match AWS increased load - scale in to match a decreased load - ensure there's a min + max # of running machines - automatically register new instances to a load balancer

Question 29

ASG Alarms

Answer 29

use cloudwatch alarms

Question 30

ASG -- Scaling Policies

Answer 30

1. target tracking 2. simple/step scaling 3. scheduled actions

Question 31

what happens during an ASG scaling cool down

Answer 31

- after a scaling activity, you are in a cool down period | - during the cool down period, you will not launch or terminal additional instances

Question 32

ASG default termination policy

Answer 32

- find the AZ which has the most # of instances - if there are multiple instances in the AZ to choose from, delete the one with the oldest launch config - ASG tries to balance the # of instances across AZ by default

Question 33

which is preferred? launch config or launch template?

Answer 33

launch template