Load Balancer Flashcards by David Dugas

Means that an application / system can handle greater loads by adapting.

Scalability

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What are the 2 types of Scalability

Vertical
Horizontal

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Icreasing the size of the instance

Vertical Scalability

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Vertical scalability is very common for ___________, such as a ____________.

non distributed systems
database

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What are 2 types of services that can scale vertically?

RDS
ElastiCache

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Is there’s usually a limit to how much you can vertically scale and WHY????

YES
Hardware limit

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Means increasing the number of instances / systems for your application

Horizontal Scalability

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____________ scaling implies distributed systems.

Horizontal

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Very common for web applications /
modern applications

Horizontal Scalability

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___________ usually goes hand in hand with horizontal scaling

High Availability

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Means running your application / system in at least 2 data centers (== Availability Zones)

High Availability

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What is the goal of high availability?

survive a data center loss

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The high availability can be _________ (for RDS Multi AZ for example)

passive

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The high availability can be _______ (for horizontal scaling)

active

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Are servers that forward traffic to multiple servers (e.g., EC2 instances) downstream

Load Balances

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READ ALL OF THESE
* 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 public traffic from private traffic

Load Balances

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

Health Checks

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The health check is done on a ______ and a ________

port
route

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If the response is not __________ (OK), then the instance is unhealthy

200

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AWS has 4 kinds of managed Load Balancers

Classic Load Balancer
Application Load Balancer
Network Load Balancer
Gateway Load Balancer

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(v1 - old generation) – 2009 – * HTTP, HTTPS,TCP,SSL(secureTCP)
* Supports TCP (Layer 4), HTTP & HTTPS (Layer 7)
* Health checks are TCP or HTTP based
* Fixed hostname XXX.region.elb.amazonaws.com

Classic Load Balancer

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(v2 - new generation) – 2016 – * HTTP, HTTPS,WebSocket
* 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)
* Suppor t for HTTP/2 and WebSocket
* Support redirects (from HTTP to HTTPS for example)

Application Load Balancer

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(v2 - new generation) – 2017
* TCP,TLS(secureTCP),UD

Network Load Balancer

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2020 –
* Operates at layer 3 (Network layer) – IP Protocol

Gateway Load Balancer

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What are the 3 ways of Application Load Balancer routing tables to different target groups

Routing based on path in URL Routing based on hostname in URL Routing based on Query String, Headers

are a great fit for micro services & container-based application (example: Docker & Amazon ECS)

Application Load Balancer (ALB)

Does ALB have a port mapping feature to redirect to a dynamic port in ECS?

YES

Application Load Balancer (v2) Target Groups (4)

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

Can ALB's route to multiple target groups

YES

For ALB's, Health checks are at what level?

target group level

READ EVERYTHING * Fixed hostname (XXX.region.elb.amazonaws.com) * The application servers don’t see the IP of the client directly * The true IP of the client is inserted in the header X-Forwarded-For * We can also get Port (X-Forwarded-Port) and proto (X-Forwarded-Proto)

Application Load Balancer (v2)

(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)

Network Load Balancer (v2)

Are used for extreme performance,TCP or UDP traffic

NLB

NLB has ______ static IP per AZ, and supports assigning Elastic IP (helpful for whitelisting specific IP)

ONE

Is NLB included in the AWS free Tier????

Network Load Balancer – Target Groups (4)

* EC2 instances * IP Addresses – must be private IPs * Application Load Balancer * Health Checks support the TCP, HTTP and HTTPS Protocols

* 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, ...

Gateway Load Balancer

Operates at Layer 3 (Network Layer) – IP Packets

Gateway Load Balancer

GLB Combines 2 of the following functions

Transparent Network Gateway – single entry/exit for all traffic Load Balancer – distributes traffic to your virtual appliances

GLB uses the _________ protocol on port ______?

GENEVE 6081

Gateway Load Balancer –Target Groups (2)

* EC2 instances * IP Addresses – must be private IPs

READ EVERYTHING * It is possible to implement stickiness so that the same client is always redirected to the same instance behind a load balancer * This works for Classic Load Balancer, Application Load Balancer, and Network Load Balancer * For both CLB & ALB, the “cookie” used for stickiness has an expiration date you control * Use case: make sure the user doesn’t lose his session data * Enabling stickiness may bring imbalance to the load over the backend EC2 instances

Sticky Sessions (Session Affinity)

2 types of Sticky Sessions – Cookie Names

Application-based Cookies Duration-based Cookies

2 types of Application-based Cookies

Custom cookie Application 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)

Custom cookie

* Generated by the load balancer * Cookie name is AWSALBAPP

Application cookie

* Cookie generated by the load balancer * Cookie name is AWSALB for ALB, AWSELB for CLB

Duration-based Cookies

* Enabled by default (can be disabled at the Target Group level) * No charges for inter AZ data

Cross-Zone Load Balancing for Application Load Balancer

* Disabled by default * You pay charges ($) for inter AZ data if enabled

Cross-Zone Load Balancing for Network Load Balancer & Gateway Load Balancer

* Disabled by default * No charges for inter AZ data if enabled

Cross-Zone Load Balancing for Classic Load Balancer

- Allows traffic between your clients and your load balancer to be encrypted in transit (in-flight encryption) - Used to encrypt connections

An SSL Certificate

What does SSL stand for??

Secure Sockets Layer

What is the newer version of SSL??

TLS

What does TLS stand for??

Transport Layer Security

You can manage SSL/TLS certificates using ________?

ACM (AWS Certificate Manager)

* You must specify a default certificate * You can add an optional list of certs to support multiple domains * Clients can use SNI (Server Name Indication) to specify the hostname they reach * Ability to specify a security policy to support older versions of SSL /TLS (legacy clients)

SSL Certificates - HTTPS listener

* Only works for ALB & NLB (newer generation), CloudFront * Does not work for CLB (older gen)

SSL – Server Name Indication (SNI)

* solves the problem of loading multiple SSL certificates onto one web server (to serve multiple websites) * It’s a “newer” protocol, and requires the client to indicate the hostname of the target server in the initial SSL handshake * The server will then find the correct certificate, or return the default one

SSL – Server Name Indication (SNI)

* Support only one SSL certificate * Must use multiple CLB for multiple hostname with multiple SSL certificates

Classic Load Balancer

* Supports multiple listeners with multiple SSL certificates * Uses Server Name Indication (SNI) to make it work

Elastic Load Balancers – SSL Certificates for Application Load Balancer (v2)

Which 2 Load Balancers * Supports multiple listeners with multiple SSL certificates * Uses Server Name Indication (SNI) to make it work

Network Load Balancer Application Load Balancer

* 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 * Between 1 to 3600 seconds (default: 300 seconds) * Can be disabled (set value to 0) * Set to a low value if your requests are short

Deregistration Delay

* In real-life, the load on your websites and application can change * In the cloud, you can create and get rid of servers very quickly

What’s an Auto Scaling Group?

READ EVERYTHING * 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)

Auto Scaling Group (ASG)

Is ASG free???

YES .. (you only pay for the underlying EC2 instances)

(3) Auto Scaling Group Attributes

A Launch Template Min Size / Max Size / Initial Capacity Scaling Policies

Is it possible to scale an ASG based on CloudWatch alarms??

YES

Auto Scaling Groups – Dynamic Scaling Policies (3)

Target Tracking Scaling Simple / Step Scaling Scheduled Actions

Auto Scaling Groups – Dynamic Scaling Policies: * Most simple and easy to set-up * Example: I want the average ASG CPU to stay at around 40%

Target Tracking Scaling

Auto Scaling Groups – Dynamic Scaling Policies: * 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

Simple / Step Scaling

Auto Scaling Groups – Dynamic Scaling Policies: * Anticipate a scaling based on known usage patterns * Example: increase the min capacity to 10 at 5 pm on Fridays

Scheduled Actions

Auto Scaling Groups - continuously forecast load and schedule scaling ahead

Predictive scaling

4 Good metrics to scale on...

* CPUUtilization: Average CPU utilization across your instances * RequestCountPerTarget: to make sure the number of requests per EC2 instances is stable * Average Network In / Out (if you’re application is network bound) * Any custom metric (that you push using CloudWatch)

After a scaling activity happens, you are in the _______?

cooldown period

What is the default cooldown period?

300 seconds

During the cooldown period, the ASG will _________?

not launch or terminate additional instances (to allow for metrics to stabilize)

Increase or decrease the current capacity of the group based on a target value for a specific metric. This is similar to the way that your thermostat maintains the temperature of your home – you select a temperature and the thermostat does the rest.

Target tracking scaling

Increase or decrease the current capacity of the group based on a set of scaling adjustments, known as step adjustments, that vary based on the size of the alarm breach.

Step scaling

Increase or decrease the current capacity of the group based on a single scaling adjustment.

Simple scaling

READ EVERYTHING 1. If there are instances in multiple Availability Zones, choose the Availability Zone with the most instances and at least one instance that is not protected from scale in. If there is more than one Availability Zone with this number of instances, choose the Availability Zone with the instances that use the oldest launch configuration. 2. Determine which unprotected instances in the selected Availability Zone use the oldest launch configuration. If there is one such instance, terminate it. 3. If there are multiple instances to terminate based on the above criteria, determine which unprotected instances are closest to the next billing hour. (This helps you maximize the use of your EC2 instances and manage your Amazon EC2 usage costs.) If there is one such instance, terminate it. 4. If there is more than one unprotected instance closest to the next billing hour, choose one of these instances at random.