ELB and ASG

Question 1

Describe scalability and compare vertical vs horizontal scalability?

Answer 1

Scalability means the system can handle greater loads by adapting
- Vertical scalability: Increasing the size/power of the underlying infra
- Horizontal scalability: Increasing the number of instances within the system

Question 2

What is an ELB?

Answer 2

An ELB is an Elastic Load Balancer which provides a singular access point which will distribute incoming traffic to multiple downstream instances

Question 3

What are the purposes of health checks?

Answer 3

Allows an Elastic Load Balancer to mark instances as unhealthy, meaning it wont be forwarded traffic

Question 4

What are the 4 types of managed load balancers?

Answer 4

1. Classic load balancer (Depreciated)
2. Application load balancer
3. Network load balancer
4. Gateway load balancer

Question 5

What layer does the ALB work on? What are the best use cases for ALB?

Answer 5

Layer 7, so it supports HTTP/HTTPS and redirects and mainly works with the url. Best supports microservices and container based applications (Docker and ECS).

Question 6

How can an application behind a application load balancer determine the IP address of the client?

Answer 6

It is stored in the X-Forwarded-For header aswell as having X-Forwarded-Port and X-Forwarded-Proto

Question 7

What layer does NLB work on? What does this mean and what are it’s main characteristics?

Answer 7

Layer 4, so deals with TCP and UDP traffic to instances. Can handle millions of requests per second and are ultra-low latency

Question 8

How many IP’s can an NLB have per AZ?

Answer 8

One static IP per AZ and supports assigning elastic ip

Question 9

What protocols does the NLB support for health checks?

Answer 9

TCP, HTTP and HTTPS

Question 10

When would you want to use a GLB?

Answer 10

When you require all traffic to come through a firewall, intrusion detection system, or deep packet inspection system

Question 11

What layer does GLB work on?

Answer 11

Layer 3, using the GENEVE protocol on port 6081

Question 12

What is the use case of a sticky session (session affinity)?

Answer 12

When you require a client to always be redirected to the same instance behind the load balancer

Question 13

What 2 cookies does sticky sessions use?

Answer 13

1. Application-based cookie (can be custom or application cookie)
2. Duration-based cookie

Question 14

Describe how traffic is distributed when cross zone load balancing is enabled versus disabled.

Answer 14

Enabled - Each load balancer instance distributes evenly across all registered instances in AZ
Disabled - Requests are only distributed across the nodes that are attached to the load balancer

Question 15

Which load balancers have cross zone load balancing enabled by default with no charges for inter AZ data, and which have it disabled with charges?

Answer 15

Application load balancer - Enabled by default with no charges
Network load balancer and Gateway load balancer - Disabled with charges

Question 16

What does Server Name Indication (SNI) allow you to do?

Answer 16

Allows you to require the client to indicate the hostname of the target serer on the initial SSL handshake allowing the webserver to find the correct certificate (requires ALB or NLB)

Question 17

What is a Deregistration Delay?

Answer 17

A configurable delay prior to terminating an EC2 instance to allow in-flight requests

Question 18

What does an ASG allow you to do?

Answer 18

Scale out (add) or scale in (remove) EC2 instances to match the load to the application aswell as managing the termination and reprovisioning of unhealthy EC2 instances

Question 19

What is the purpose of a launch template for ASG’s?

Answer 19

Define things like the AMI/Instance type, EC2 User Data, EBS volumes, security groups etc

Question 20

What service enables auto scaling with ASG?

Answer 20

CloudWatch alarms can be configured to track metrics like Average CPU (or custom metrics) to calculate the number of instances that should be running

Question 21

What two types of scaling fall under dynamic scaling?

Answer 21

1. Target tracking - Average CPU to stay around X
2. Simple / step - When a CloudWatch alarm is triggered, add X units

Question 22

If you are aware of patterns in traffic coming to your application, what scaling method could be useful?

Answer 22

Scheduled scaling - Increase capacity to X at 5pm on Fridays

Question 23

What scaling method allows AWS to automatically scale your application based on forecasted traffic?

Answer 23

Predictive scaling

Question 24

Shortly after a scaling activity occurs, the traffic to the application drastically falls however no new scaling activity occurs. What is a possible cause?

Answer 24

The cooldown period (default of 300 seconds) is a period of time where no new scaling activity will occur after a scaling activity is completed.

Question 25

Suppose you need to relaunch all EC2 instances within an ASG due to an updated launch template, how can this be achieved?

Answer 25

Use the instance refresh feature which will roll out the update periodically