Load Balancers

Question 1

Elastic Load Balancer (ELB)

Answer 1

automatically distributes incoming application traffic across multiple targets
- can be done across multiple AZs

Question 2

ELB Health Checks

Answer 2

• all load balancers can be configured with health checks
• sees which instances are healthy or unhealthy
• stops sending requests to unhealthy requests (until they become healthy)

Question 3

Application Load Balancer

Answer 3

• http & https
• INTELLIGENT
• layer 7

Question 4

Network Load Balancer

Answer 4

• layer 4 (connection level)
• millions of requests per second
• ultra-low latencies

Question 5

Classic Load Balancer

Answer 5

• legacy
• http/https
• deprecated
• EOL Aug 2022

Question 6

ALB - listeners

Answer 6

check for connection requests from clients using the protocol and port you configure

• http: port 80
• https: port 443 w/ SSL certificate

Question 7

ALB - rules

Answer 7

when conditions are met, then actions are performed

- each listener requires you to provide a default rule

Question 8

ALB - target groups

Answer 8

route requests to one or more registered targets, such as EC2 instances, using the protocol and port you specify

Question 9

How does https load balancing work?

Answer 9

• uses port 443
• you must deploy at least one SSL/TLS certificate on your load balancer
• Load balancer uses a server certificate to terminate the front end connection, then decrypts requests from clients before sending them to the targets *

Question 10

ALB Path-based routing - common exam scenario

Answer 10

Application Load balancer can determine which instance (target) to send user to based on path or url using path patterns

ex:
- send www.myurl.com to us-east-1a
- send www.myurl.com/images to us-east-1b

Question 11

Network Load Balancers Protocols

Answer 11

TCP, TLS, UDP, TCP_UDP

Question 12

Network Load Balancer Ports

Answer 12

1 - 65535

Question 13

How many requests per second can Network Load Balancer handle?

Answer 13

millions

Question 14

How are listeners different on NLBs than ALBs?

Answer 14

• ALB listeners are intelligent and can check rules

- NLB listeners do not have rules, they are not intelligent, they only forward the request to the target group

Question 15

Network Load Balancer Encryption

Answer 15

• can use a TLS listener to offload the work of encryption and decryption to your load balancer
• if the listener protocol is TLS, you must deploy exactly 1 SSL certificate on the listener

Question 16

Layer 4 Exam tips

Answer 16

• layer 4 = extreme performance
• other cases for ports other than 80 and 443
• can decrypt traffic, but must install certificate on the NLB

Question 17

Classic Load Balancer

Answer 17

• you can choose layer 7 or Layer 4

Question 18

X-Forwarded-For (Classic Load Balancer)

Answer 18

header used to see the IP v4 where original request came from

Question 19

Classic Load Balancer Gateway Timeouts

Answer 19

• 504 error

load balancer is running, but can’t connect to the web or database layer

Question 20

Sticky Sessions for Classic Load Balancer

Answer 20

• Classic Load Balancer
• allows you to bind a user session to a specific Ec2 instance
• ensures all requests are sent to same instance so you can store data locally to that instance

Question 21

Problems of Sticky Sessions on Classic Load Balancer

Answer 21

• if the instance is unhealthy or terminated, the user still gets routed there. To solve this, disable sticky sessions

Question 22

Difference of Sticky Sessions on ALBs rather than CLBs

Answer 22

• ALBs have sticky sessions, but they route to the target group, not to individual instances

Question 23

Deregistration Delay/Connection Draining

Answer 23

allows load balancers to keep existing connections open if the EC2 instance is de-registered or becomes unhealthy

• lets the load balncer complete in-flight requests made to unhealthy instances
• can be disabled if you want connections immediately closed*