AWS Fundamentals: ELB + ASG

Question 1

What does “Scalability” mean?

Answer 1

An application’s / system’s ability to handle greater loads by adapting

Question 2

Two kinds of scalability?

Answer 2

1. Horizontal - elasticity
2. Vertical

Question 3

Vertical Scalability means..

Answer 3

increasing the size of your instance

Question 4

What is “Vertical Scalability” common for?

Answer 4

Non distributed system such as a database

Question 5

What are the limits of “Vertical Scalability”

Answer 5

Hardware limits

Question 6

Horizontal Scalability means…

Answer 6

increasing the number of instances/systems for your application

Question 7

What is “distributed systems”?

Answer 7

a collection of computer programs that work together to complete a task or provide a service.

Question 8

Horizontal Scaling implies…

Answer 8

you have distributed systems

Question 9

What is “High Availability”?

Answer 9

Running your application / system in at least two data centers (availability zones)

Question 10

Main goal of “high availability”

Answer 10

survive data center loss

Question 11

What is “load balancing”?

Answer 11

servers(behind the scene servers) forward traffic to multiple servers (e.g. EC2 instances) downstream

Question 12

Why use a load balancer?

Answer 12

• Spread load across multiple downstream instances
• Expose a single point of access (DNS) to your application
• Seamlessly handle failures of downstream instances
• Provide SSL termination (HTTPS) for you websites
• Enforce stickiness with cookies
• High availability across zones
• Separate public traffic from private traffic

Question 13

What is an “elastic load balancer”?

Answer 13

A managed load balancer that:
- AWS guarantees that it will be working
- AWS takes care of upgrades, maintenance, high availability
- AWS provides only a few configuration knobs

Question 14

What are “Health Checks”?

Answer 14

Enables the load balancer to know if instances it forwards traffic to are available to reply to requests

Question 15

Where are health checks done?

Answer 15

on a port and a route (/health is common)

Question 16

4 types of load balancers on AWS:

Answer 16

1.Classic Load Balancer(deprecated)

2. Application Load Balancer
3. Network Load bBalancer
4. Gateway Load Balancer

Question 17

Some load balancers can be set up as ….. or …….. ELBs

Answer 17

internal (private), external (public)

Question 18

Users can access your load balancer from……. using…… or……..

Answer 18

anywhere, HTTP, HTTPS

Question 19

EC2 instances should only allow traffic coming directly from the load balancer.

Answer 19

True

Question 20

How does an ECS instance allow only a load balancer to forward traffic to it?

Answer 20

With a security group

Question 21

What does an ALB forward traffic to?

Answer 21

Multiple HTTP applications across machines (target group)
or
multiple applications on the same machine (ex: containers)

Question 22

What are the 3 different target groups that routing can be based on?

Answer 22

1. Routing based on path in URL
2. Routing based on hostname in URL
3. Routing based on query strings, headers

Question 23

Features:
- EC2 instances (can be managed by Auto Scaling Group) - HTTP

• ECS tasks ( managed by ECS itself) - HTTP
• Lambda functions - HTTP request is translated into a JSON event
• IP addresses - must be private IPs
• ALB can route to multiple target groups

Answer 23

Application Load Balancer (v2) Target Groups

Question 24

ALB can route to multiple target groups?

Answer 24

True

Question 25

Where are health checks done?

Answer 25

At the target group level

Question 26

ALB has a Fixed host name?

Answer 26

True

Question 27

The application servers don’t see the IP of the client directly?

Answer 27

True

Question 28

Where can the true IP of the clients be found?

Answer 28

in the header X-Forwarded-For.

Question 29

What does a Network Load Balancer allow?

Answer 29

• Forward TCP & UDP traffic to your instances
• Handle millions of request per seconds
• Less latency ~100 ms (vs 400 ms for ALB)

Question 30

What are NLB used for?

Answer 30

Extreme performance,TCP or UDP traffic

Question 31

Features:
- EC2 instances
- IP Addresses – must be private IPs
- Application Load Balancer

Answer 31

Network Load Balancer – Target Groups

Question 32

What is the idea of “Sticky Sessions”?

Answer 32

the same client is always redirected to the same instance behind a load balancer

Question 33

Which load balancers does sticky sessions work with?

Answer 33

• Classic Load Balancer
• Application Load Balancer
• Network Load
  Note:
  NLB works without cookies

Question 34

Which load balancers have a “cookie” that expires?

Answer 34

CLB & ALB. User controls “cookie” expiration.