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AWS Certified Developer Associate > ELB + ASG Fundamentals > Flashcards

ELB + ASG Fundamentals Flashcards

1
Q

What is load balancing?

A

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

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2
Q

Why use a load balancer?

A
  • 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
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3
Q

What is Elastic Load Balancer?

A

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 is integrated with many AWS offerings / services

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4
Q

What are Health Checks?

A

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

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5
Q

When can we say the insance is unhealty?

A

If the health check response is not OK (200).

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6
Q

What are the 3 (4) types of ELBs?

A
  • Classic Load Balancer (v1 - old generation) – 2009 – CLB (DEPRECATED)
  • HTTP, HTTPS, TCP, SSL (secure TCP)
  • Application Load Balancer (v2 - new generation) – 2016 – ALB
  • HTTP, HTTPS, WebSocket
  • Network Load Balancer (v2 - new generation) – 2017 – NLB
  • TCP, TLS (secure TCP), UDP
  • Gateway Load Balancer – 2020 – GWLB
  • Operates at layer 3 (Network layer) – IP Protocol
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7
Q

What is a Load Balancer Security Group?

A

It accepts the HTTP/HTTPS request from users and forwards the HTTP call to the downstream. The application only accept traffic from the LB.

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8
Q

How to redirect LB to instances?

A

Create Target groups.

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9
Q

How to disable request directly to App Server, but enable the LB?

A

In the App server Security Group, remove the incoming request, add a new one with the LB Security Group only.

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10
Q

What is ALB?

A

Application Load Balancer is a Layer 7 (HTTP) load balancer.

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11
Q

What are the features of ALB?

A
  • 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)
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12
Q

What kind of routing is supported for ALB?

A

Routing tables to different target groups:
* Routing based on path in URL (example.com/users & example.com/posts)
* Routing based on hostname in URL (one.example.com & other.example.com)
* Routing based on Query String, Headers (example.com/users?id=123&order=false)

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13
Q

What is ALB good for?

A
  • 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
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14
Q

What can be part of a Target Group?

A
  • 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
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15
Q

Is health check per instances?

A

No, healt check is for target group level.

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16
Q

Can we see the IP of the client if we use ALB?

A

Yes, in the X-Forwarded-For header.

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17
Q

What layer is used by the Network Load Balancer?

A

The layer 4, TCP & UDP traffic. 100ms latency. Million requests / seconds.

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18
Q

How many IP can be assigned to NLB?

A

One NLB has 1 static IP per AZ, supports Elasctic IP.

19
Q

Why is NLB used?

A

For extreme performance, TCP and UDP traffic.

20
Q

What can be in an NLB Target Group?

A
  • EC2 instances
  • Private IP addresses
  • ALBs
21
Q

What are the Health Check supports in NLB target groups?

A

They support TCP, HTTP os HTTPS.

22
Q

What is the usage of Gateway Load Balancer?

A
  • 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
23
Q

What layer does GLB operate?

A

It operates on the layer 3, IP packets

24
Q

What functions are combined in GLB?

A
  • Transparent Network Gateway: single entry/exit for all traffic
  • Load Balancer: distributes traffic to your virtual appliances
25
Q

What protocol does GLB use?

A

Uses the GENEVE protocol on 6081

26
Q

What are the target groups for GLB?

A
  • EC2 instances
  • Private IP addresses
27
Q

What is ELB Sticky Sessions / Session Affinity?

A

It is possible to implement stickiness so that the
same client is always redirected to the same
instance behind a load balancer.

28
Q

What ELBs supports Sticky Sessions?

A

ALB, NLB

29
Q

Whats the typical Sticky Sessions use case?

A

Its used to make sure users doesn’t load session data (e.g. login credentials)

30
Q

What are the prohibited cookie names if ALB is configured?

A

AWSALB, AWSALBAPP, or AWSALBTG

31
Q

What is ELB Cross-Zone Load Balancing?

A

If configured, the load balancer will distribute the load EVENLY across all AZ.

32
Q

Can you use Cross-Zone Load Balancing in all types of ELB?

A

yes, but
* Application Load Balancer
* Enabled by default (can be disabled at the Target Group level)
* No charges for inter AZ data
* Network Load Balancer & Gateway Load Balancer
* Disabled by default
* You pay charges ($) for inter AZ data if enabled

33
Q

How SSL Certificates used in ELB?

A

The LB uses the certificate to use HTTPS.
* Manage certificates in ACM
* For each HTTPS listener (TG):
* Must specify a default cert
* Use SNI to spec. the hostname they reach

34
Q

What is SSL Server Name Indication (SNI)?

A
  • 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
35
Q

What is Deregistration Delay / Connection Draining?

A
  • 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
36
Q

What are the Auto Scaling Groups(ASG)?

A
  • 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)
  • ASG are free (you only pay for the underlying EC2 instances)
37
Q

What are the ASG Attributes?

A
  • A Launch Template
  • Min Size / Max Size / Initial Capacity
  • Scaling Policies
38
Q

What are ASG Launch Tempaltes?

A
  • 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
39
Q

How to AutoScaling with CloudWatch?

A

It is possible to scale an ASG based on CloudWatch alarms
* An alarm monitors a metric (such as Average CPU, or a custom metric)
* Metrics such as Average CPU are computed for the overall ASG instances

40
Q

What are ASG Dynamic Scaling Policies?

A
  • Target Tracking Scaling => Target resource usage (CPU > 50%)
  • Simple / Step Scaling => CW alarm triggered, then add 2 unit
  • Scheduled Actions => At a time increase min units
41
Q

What is ASG Predictive Scaling?

A

Machine Learning driven scaling. It will forecast the load and scale the LB.

42
Q

What are the good ASG metrics?

A
  • 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)
43
Q

What is ASG Scaling Cooldown

A
  • 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)
44
Q

What is ASG Instance Refresh?

A

Goal: update launch template
and then re-creating all EC2
instances
* For this we can use the native
feature of Instance Refresh
* Setting of minimum healthy
percentage
* Specify warm-up time (how long
until the instance is ready to use)

AWS Certified Developer Associate (17 decks)

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