AWS Fundamentals – Part II

Question 1

What is Scalability?

Answer 1

• Scalability means that an application / system can handle greater loads by adapting.
• There are two kinds of scalability:
  • Vertical Scalability
  • Horizontal Scalability (= elasticity)
• Scalability is linked but different to High Availability

Question 2

What is Vertical Scalability?

Answer 2

• Increasing the size of the instance
• Vertical scalability is very common for non distributed systems, such as a database.
• RDS, ElastiCache are services that can scale vertically.
• There’s usually a limit to how much you can vertically scale (hardware limit)

Question 3

What is Horizontal Scalability?

Answer 3

• Horizontal Scalability means increasing the number of instances / systems for your application
• Horizontal scaling implies distributed systems.
• This is very common for web applications modern applications
• It’s easy to horizontally scale thanks the cloud offerings such as Amazon EC2

Question 4

What is High Availability?

Answer 4

• High Availability usually goes hand in hand with horizontal scaling
• High availability means running your application / system in at least 2 data centers (AZ)
• The goal of high availability is to survive a data center loss
• The high availability can be passive (for RDS Multi AZ for example)
• The high availability can be active (for horizontal scaling)

Question 5

Vertical Scaling for EC2 instance

Answer 5

Vertical Scaling: Increase instance size (= scale up / down)
• From: t2.nano - 0.5G of RAM, 1 vCPU
• To: u-12tb1.metal – 12.3 TB of RAM, 448 vCPUs

Question 6

Horizontal Scaling for EC2 instance

Answer 6

Horizontal Scaling: Increase number of instances (= scale out / in)
• Auto Scaling Group
• Load Balancer

Question 7

High Availability for EC2 instance:

Answer 7

High Availability: Run instances for the same application across multi AZ
• Auto Scaling Group multi AZ
• Load Balancer multi AZ

Question 8

What is Load balancer?

Answer 8

Load Balances are servers that forward traffic to multiple servers (e.g., EC2 instances) downstream

Question 9

Why use a load balancer?

Answer 9

• Spread load across multiple downstream instances
• Expose a single point of access (DNS) to your application
• Seamlessly handle failures of downstream instances
• Do regular health checks to your instances
• Provide SSL termination (HTTPS) for your websites
• Enforce stickiness with cookies
• High availability across zones
• Separate traffic: publicf rom private

Question 10

What is ELB and why yo use it?

Answer 10

• Elastic Load Balancer is a managed load balancer
  • AWS guarantees that it will be working
  • AWS takes care of upgrades, maintenance, high availability
  • AWS provides only a few configuration knobs
• It costs less to setup your own load balancer but it will be a lot more effort on your end
• It is integrated with many AWS offerings / services
  • EC2, EC2 Auto Scaling Groups, Amazon ECS
  • AWS Certificate Manager (ACM), CloudWatch
  • Route 53, AWS WAF, AWS Global Accelerator

Question 11

What are Health Checks?

Answer 11

• Health Checks are crucial for Load Balancers
• They enable the load balancer to know if instances: forwards traffic to. Are available to reply to requests
• The health check is done on a port and a route (/health is common)
• If the response is not 200 (OK), then the instance is unhealthy

Question 12

4 types of load balancer on AWS:

Answer 12

1. Classic Load Balancer (v1 - old generation) – 2009 – CLB
   • HTTP, HTTPS, TCP, SSL (secure TCP)
2. Application Load Balancer (v2 - new generation) – 2016 – ALB
   • HTTP, HTTPS, WebSocket
3. Network Load Balancer (v2 - new generation) – 2017 – NLB
   • TCP, TLS (secure TCP), UDP
4. Gateway Load Balancer – 2020 – GWLB
   • Operates at layer 3 (Network layer) – IP Protocol

Question 13

What is CLB?

Answer 13

• Supports TCP (Layer 4), HTTP & HTTPS (Layer 7)
• Health checks are TCP or HTTP based
• Fixed hostname XXX.region.elb.amazonaws.com

Question 14

What is ALB?

Answer 14

• Application load balancers is Layer 7 (HTTP)
• Load balancing to multiple HTTP applications across machines (target groups)
• Load balancing to multiple applications on the same machine (ex: containers)
• Support for HTTP/2 and WebSocket
• Support redirects (from HTTP to HTTPS for example)
• Routing tables to different target groups
• ALB are a great fit for micro services & container-based application (example: Docker & Amazon ECS)
• Has a port mapping feature to redirect to a dynamic port in ECS
• In comparison, we’d need multiple Classic Load Balancer per application

Question 15

What are the ALB target groups?

Answer 15

• EC2 instances (can be managed by an 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
• Health checks are at the target group level

Question 16

What is NLB? What it allow?

Answer 16

Network load balancers (Layer 4) allow to:
• Forward TCP & UDP traffic to your instances
• Handle millions of request per seconds
• Less latency ~100 ms (vs 400 ms for ALB)

Question 17

How many static IP’s does the NLB has?

Answer 17

NLB has one static IP per AZ, and supports assigning Elastic IP

Question 18

When we will use NLB?

Answer 18

NLB are used for extreme performance, TCP or UDP traffic

Question 19

Is the NLB free?

Answer 19

Not included in the AWS free tier

Question 20

What is GWLB?

Answer 20

Gateway Load Balancer

• Deploy, scale, and manage a fleet of 3rd party network virtual appliances in AWS
• Example: Firewalls, Intrusion Detection and Prevention Systems, Deep Packet Inspection Systems, payload manipulation, …

Question 21

GWLB

Answer 21

• Operates at Layer 3 (Network Layer) – IP Packets
• Combines the following functions:
  • Transparent Network Gateway – single entry/exit for all traffic
  • Load Balancer – distributes traffic to your virtual appliances
• Uses the GENEVE protocol on port 6081

Question 22

What to remember about IP in GWLB – Target Groups

Answer 22

Question 23

What is Sticky Sessions (Session Affinity)?

Answer 23

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

Question 24

What is the use case for sticky sessions?

Answer 24

Use case: make sure the user doesn’t lose his session data

Question 25

What can work with Sticky Sessions?

Answer 25

This works for Classic Load Balancers & Application Load Balancer

Question 26

How much time the “cookie” expiration date?

Answer 26

The “cookie” used for stickiness has an expiration date you control

Question 27

At Application-based Cookies What are the properties?

Answer 27

**Application-based Cookies** • Custom cookie • Generated by the target • Can include any custom attributes required by the application • Cookie name must be specified individually for each target group • Don’t use AWSALB, AWSALBAPP, or AWSALBTG (reserved for use by the ELB)

Question 28

How generate the an Application cookie and what is the name of the cookie?

Answer 28

**Application cookie** • Generated by the load balancer • Cookie name is AWSALBAPP

Question 29

Duration-based Cookies - How generate them and what is the name?

Answer 29

Duration-based Cookies • Cookie generated by the load balancer • Cookie name is AWSALB for ALB, AWSELB for CLB

Question 30

Cross-Zone Load Balancing - how does it distributes?

Answer 30

With Cross Zone Load Balancing: each load balancer instance distributes evenly across all registered instances in all AZ

Question 31

How does Cross-Zone Load Balancing works with: ALB, NLB, CLB?

Answer 31

**Application Load Balancer** • Always on (can’t be disabled) • No charges for inter AZ data **Network Load Balancer** • Disabled by default • You pay charges ($) for inter AZ data if enabled **Classic Load Balancer** • Disabled by default • No charges for inter AZ data if enabl

Question 32

What is SSL

Answer 32

SSL refers to Secure Sockets Layer, used to encrypt connections

Question 33

What is TLS

Answer 33

TLS refers to **Transport Layer Security,** which is a newer version

Question 34

What is SNI? what it come to solve? who it works and doesn't work with?

Answer 34

**Server Name Indication** SNI solves the **problem of loading multiple SSL certificates** onto one web server Only works for ALB & NLB (newer generation), CloudFront • Does not work for CLB (older gen)

Question 35

How does ELB, ALB, NLB, works with SSL Certificates?

Answer 35

**Classic Load Balancer (v1)** • Support only **one SSL certificate** • Must u**se multiple CLB for multiple hostname with multiple SSL certificates** **Application Load Balancer (v2)** • Supports **multiple** **listeners** with **multiple** SSL **certificates** • Uses Server Name Indication (**SNI**) to make it work **Network Load Balancer (v2)** • Supports **multiple** **listeners** with **multiple** SSL **certificates** • Uses Server Name Indication (**SNI**) to make it work

Question 36

What is Connection Draining?

Answer 36

Time to complete “in-flight requests” while the instance is de-registering or unhealthy Stops sending new requests to the EC2 instance which is de-registering

Question 37

What is the Connection Draining Feature naming?

Answer 37

Feature naming • Connection Draining – for CLB • Deregistration Delay – for ALB & NLB

Question 38

Is Connection Draining can be disable?

Answer 38

Can be disabled (set value to 0)

Question 39

what is The goal of an ASG?

Answer 39

The goal of an **Auto Scaling Group** (ASG) is to: • **Scale out** (add EC2 instances) to match an increased load • **Scale in** (remove EC2 instances) to match a decreased load • Ensure we have a minimum and a maximum number of EC2 instances **running** • **Automatically register** new instances to a **load balancer** • **Re-create an EC2 instance** in case a previous one is terminated (ex: if unhealthy)

Question 40

What is the cost ASG?

Answer 40

ASG are free (you only pay for the **underlying** **EC2 instances**)

Question 41

What are the ASG attributes?

Answer 41

**A Launch Template** (older “Launch Configurations” are deprecated) • AMI + Instance Type • EC2 User Data • EBS Volumes • Security Groups • SSH Key Pair • IAM Roles for your EC2 Instances • Network + Subnets Information • Load Balancer Information **Min Size / Max Size / Initial Capacity** **Scaling Policies**

Question 42

ASG –Four types of Dynamic Scaling Policies?

Answer 42

* **Target Tracking Scaling** • Most simple and easy to set-up • Example: I want the average ASG CPU to stay at around 40% * **Simple / Step Scaling** • When a CloudWatch alarm is triggered (example CPU \> 70%), then add 2 units • When a CloudWatch alarm is triggered (example CPU \< 30%), then remove 1 * **Scheduled Action**s • Anticipate a scaling based on known usage patterns • Example: increase the min capacity to 10 at 5 pm on Fridays * **Predictive scaling** • continuously forecast load and schedule scaling ahead

Question 43

What is the “cooldown period" after scaling with ASG? What is the advice?

Answer 43

After a scaling activity happens, you are in the cooldown period (default 300 seconds) During the cooldown period, the ASG will not launch or terminate additional instances (to allow for metrics to stabilize) Advice: Use a ready-to-use AMI to reduce configuration time in order to be serving request fasters and reduce the cooldown period