Build a Three-Tier Cloud Application Architecture

A production cloud application is rarely just one virtual machine. Real enterprise applications are commonly separated into multiple tiers so that presentation, application logic, and data can be scaled, secured, monitored, and managed independently.

Welcome to Lab 12 of the CompTIA Cloud+ practical lab sequence.

This is an important milestone.

In the previous labs, you built individual cloud capabilities:

virtual machines
segmented networks
routing
internet access
security groups
DNS
block, file, and object storage
storage security
IAM
MFA and privileged access
workload identities

Now you will bring these components together into one architecture.

You will build:

                    Internet
                       ↓
                   Web Tier
                       ↓
               Application Tier
                       ↓
                  Data Tier

The objective is not simply:

Deploy three servers.

The objective is:

Understand how enterprise cloud components work together to create a segmented, least-privilege, service-oriented application architecture.

🎯 Mission Information

Item	Details
Lab	12 — Build a Three-Tier Cloud Application Architecture
Difficulty	Intermediate
Estimated Time	120–180 Minutes
Certification Alignment	CompTIA Cloud+
Primary Focus	Cloud Application Architecture
Previous Lab	11 — Workload Identity and Service Account Lab
Career Alignment	Cloud Administrator, Cloud Engineer, Cloud Security Engineer, Solutions Architect
Major Skills	Architecture, Compute, Networking, IAM, DNS, Security, Storage, Troubleshooting
Deliverable	Working Three-Tier Architecture + Architecture Review

🏢 Scenario

Your organization is moving a small internal business application into the cloud.

The application contains three logical components:

Web Tier

Responsible for:

receiving user requests
serving web content
forwarding application requests

Application Tier

Responsible for:

business logic
processing
communication with backend services

Data Tier

Responsible for:

persistent application data

Your manager requires the following architecture:

Internet
   ↓
Web Tier
   ↓
Application Tier
   ↓
Database Tier

Security requirements include:

only the web tier should require direct inbound internet access
application workloads must remain private
database workloads must remain private
web tier should communicate only with the required application service
application tier should communicate only with the required database service
direct web-to-database communication should not be required
workload identities should replace embedded cloud credentials
DNS names should be used instead of hard-coded infrastructure IP addresses
all resources should follow established naming, tagging, and documentation standards

🎯 Lab Objectives

By completing this lab, you should be able to:

explain three-tier architecture
identify presentation, application, and data tiers
deploy workloads into appropriate subnets
distinguish public and private workload placement
configure tier-specific security groups
validate routing
use private DNS between tiers
understand application traffic flows
use workload identities
apply least privilege
understand application storage requirements
validate tier-to-tier connectivity
identify broken dependencies
troubleshoot multi-tier applications systematically
document enterprise architecture
perform a basic security review
perform a basic availability review
explain three-tier architectures during interviews

🧠 Why Three-Tier Architecture?

A simple application might begin as:

Internet
   ↓
Single Server
   |
   ├── Web
   ├── Application
   └── Database

This may be acceptable for a small lab.

But it creates several limitations.

If the server fails:

everything fails.

If the web component is compromised:

the application and database may be directly exposed.

If the web tier needs more capacity:

you may have to scale the entire system.

A three-tier design separates responsibilities.

Presentation
      ↓
Application Logic
      ↓
Data

🧠 Architectural Benefits

Three-tier designs can improve:

security
scalability
availability
troubleshooting
workload isolation
operational ownership

01 — Understand the Three Tiers

Your application will contain:

Tier 1
Web / Presentation

Tier 2
Application / Business Logic

Tier 3
Database / Data

02 — Understand the Web Tier

The web tier receives client traffic.

Conceptually:

User
 ↓
HTTPS
 ↓
Web Server

Typical responsibilities include:

serving HTML
accepting HTTP/HTTPS requests
proxying requests
presenting application responses

03 — Understand the Application Tier

The application tier processes business logic.

Conceptually:

Web Tier
   ↓
Application Request
   ↓
Application Service

The application tier should generally not require direct inbound access from arbitrary internet clients.

04 — Understand the Data Tier

The data tier stores application information.

Conceptually:

Application Tier
      ↓
Database Protocol
      ↓
Database

The database should normally be one of the most restricted components.

05 — Review the Existing Cloud Network

From previous labs, you should already have:

10.10.0.0/16
    |
    ├── Public
    │   10.10.10.0/24
    |
    ├── Application
    │   10.10.20.0/24
    |
    └── Database
        10.10.30.0/24

06 — Verify the Existing Components

Confirm:

Virtual Network
      ↓
Public Subnet
      ↓
Application Subnet
      ↓
Database Subnet

Also verify:

route tables
security groups
private DNS
IAM/workload identity
storage resources

07 — Define the Architecture Before Deployment

Create the target architecture:

                         Internet
                            |
                         HTTPS
                            |
                            v
                 +--------------------+
                 | Web Tier           |
                 | 10.10.10.0/24      |
                 +--------------------+
                            |
                    Application Port
                            |
                            v
                 +--------------------+
                 | Application Tier   |
                 | 10.10.20.0/24      |
                 +--------------------+
                            |
                      Database Port
                            |
                            v
                 +--------------------+
                 | Database Tier      |
                 | 10.10.30.0/24      |
                 +--------------------+

08 — Define the Traffic Requirements

Before deployment, document the expected communication.

Source	Destination	Service	Expected
Internet	Web	HTTPS	Allow
Internet	Application	Any	Deny
Internet	Database	Any	Deny
Web	Application	Application Port	Allow
Web	Database	Database Port	Deny
Application	Database	Database Port	Allow
Admin	Workloads	Management	Controlled

🧠 Important

You are designing:

application communication

before configuring:

network rules.

09 — Define the Resource Names

Use your established naming standards.

Example:

cloudplus-lab-web-01

cloudplus-lab-app-01

cloudplus-lab-db-01

10 — Apply Standard Tags

Use:

Tag	Value
Environment	Lab
Course	CompTIA-CloudPlus
Application	ThreeTierLab
Owner	Student
Purpose	Training

Add tier information if supported:

Tier = Web

Tier = Application

Tier = Database

11 — Deploy the Web Workload

Deploy a small Linux VM into:

10.10.10.0/24

Example:

cloudplus-lab-web-01

Use a small general-purpose instance.

12 — Configure Web Networking

The web VM should have:

private IP
public connectivity where required
web-tier security group
correct route table

Record:

VM:

Private IP:

Public IP:

Subnet:

Security Group:

DNS Name:

13 — Install a Simple Web Service

Use a simple supported web server or lightweight training service.

Possible examples include:

Nginx
Apache
another approved web service

The objective is not application development.

It is:

architecture validation.

14 — Create a Basic Web Page

Create a simple page displaying:

CompTIA Cloud+ Three-Tier Lab

Web Tier:
Healthy

15 — Validate Local Web Service

From the VM itself, confirm the web service responds.

For example:

curl http://localhost

Use HTTPS where your lab supports it.

16 — Validate External Web Access

From an approved client, access the public web endpoint.

Expected:

Internet
   ↓
Web Tier
   ↓
SUCCESS

17 — Deploy the Application Workload

Create:

cloudplus-lab-app-01

inside:

10.10.20.0/24

Do not assign a public IP unless your lab architecture specifically requires one.

18 — Validate Application Placement

Confirm:

Application VM
      ↓
Private IP
      ↓
Application Subnet
      ↓
No Direct Public Exposure

19 — Install a Simple Application Service

Create a lightweight service that listens on a dedicated application port.

For example:

TCP 8080

You may use another safe lab port.

The service can simply return:

Application Tier:
Healthy

20 — Validate the Application Locally

From the application VM:

curl http://localhost:8080

Expected:

successful response.

21 — Configure the Application Security Group

Allow:

Web Tier
   ↓
TCP 8080
   ↓
Application Tier

Do not allow:

Internet
   ↓
TCP 8080
   ↓
Application Tier

22 — Validate Web-to-App Connectivity

From the web VM:

curl http://<app-private-ip>:8080

Expected:

successful.

23 — Validate Internet-to-App Restriction

Confirm the application VM is not directly accessible from the internet.

Expected:

Internet
   X
Application

24 — Create the Application DNS Record

Using the private DNS zone from Lab 06, create:

app.cloudplus.lab
      ↓
<Application Private IP>

25 — Validate DNS

From the web VM:

nslookup app.cloudplus.lab

Expected:

correct application private IP.

26 — Replace the Hard-Coded IP

Instead of:

http://10.10.20.10:8080

use:

http://app.cloudplus.lab:8080

🧠 Architecture Improvement

Your web tier now depends on:

a logical service name

instead of:

a specific infrastructure IP.

27 — Deploy the Data-Tier Workload

For this Cloud+ architecture lab, you can use either:

a small database VM
an approved managed database service
a lightweight simulated database endpoint

Keep the lab cost low.

Example VM name:

cloudplus-lab-db-01

28 — Place the Database in the Correct Subnet

The database belongs in:

10.10.30.0/24

Do not assign unnecessary public access.

29 — Record Database Configuration

Database:

Private IP:

Subnet:

Security Group:

Public IP:
None

DNS:
db.cloudplus.lab

30 — Install or Configure the Database Service

Use an approved lightweight database appropriate for your lab.

The exact database technology is less important than understanding:

Application
      ↓
Database Service
      ↓
Persistent Data

31 — Identify the Database Port

Record the selected database protocol/port.

Example possibilities include:

Use only the port for your actual test service.

32 — Configure the Database Security Group

Allow:

Application Tier
      ↓
Required DB Port
      ↓
Database Tier

Do not allow:

Web Tier
      ↓
Database

unless specifically required.

33 — Validate App-to-DB Connectivity

From the application server, test the database service using an appropriate client or simple connectivity test.

Expected:

Application
      ↓
Database
      ↓
SUCCESS

34 — Validate Web-to-DB Restriction

From the web server, test the database port.

Expected:

Web
   X
Database

35 — Validate Internet-to-DB Restriction

Confirm:

Internet
   X
Database

36 — Create the Database DNS Record

Create:

db.cloudplus.lab
      ↓
<Database Private IP>

37 — Validate the Database DNS Record

From the application VM:

nslookup db.cloudplus.lab

Expected:

correct database private IP.

38 — Replace Database IP References

Applications should use:

db.cloudplus.lab

rather than:

10.10.30.10

39 — Build the Service Chain

Your application now follows:

User
 ↓
web.cloudplus.lab
 ↓
Web Tier
 ↓
app.cloudplus.lab
 ↓
Application Tier
 ↓
db.cloudplus.lab
 ↓
Database Tier

40 — Understand End-to-End Request Flow

A user request may follow:

1. User resolves web endpoint

2. User connects to Web Tier

3. Web Tier calls Application Tier

4. Application Tier performs business logic

5. Application Tier queries Database Tier

6. Database returns data

7. Application returns response

8. Web Tier returns response to user

🧠 Cloud Engineer Skill

You should be able to explain:

every dependency in this path.

41 — Add Workload Identity to the Application Tier

Use the workload identity created in Lab 11 where appropriate.

Conceptually:

Application VM
      ↓
cloudplus-app-identity
      ↓
Scoped Cloud Permission

42 — Define the Workload Requirement

Perhaps the application needs to read objects from:

cloudplus-lab-objects

Grant only:

Read Approved Storage

43 — Validate Workload Access

From the application workload:

Application
      ↓
Workload Identity
      ↓
Approved Storage
      ↓
READ ALLOWED

44 — Validate Unrelated Access Is Denied

Confirm the workload cannot perform unrelated operations such as:

Manage IAM

Delete Network

Delete VM

🧠 Architecture Connection

You now have:

Network Segmentation
+
Workload Identity
+
Least Privilege

working together.

45 — Review Storage Requirements

The application may use:

Block Storage

for VM filesystems.

Object Storage

for objects, documents, static assets, or backups.

Database Storage

for structured application data.

46 — Identify Where Each Data Type Belongs

Create:

Data	Storage Model
VM OS	Block
Database Data	Block/Managed DB Storage
Shared Application Assets	File where required
Images/Documents	Object
Backup Objects	Object

47 — Understand Tier-Specific Responsibilities

Web tier should focus on:

Presentation

Application tier:

Business Logic

Database tier:

Persistence

48 — Avoid Cross-Tier Shortcuts

Poor design:

Web
 ↓
Database

Better:

Web
 ↓
Application
 ↓
Database

where that matches the application’s intended architecture.

49 — Review Network Security End to End

Your security path should resemble:

Internet
      ↓
HTTPS
      ↓
Web
      ↓
App Port
      ↓
Application
      ↓
DB Port
      ↓
Database

50 — Build the Security Rule Matrix

Source	Destination	Port	Expected
Internet	Web	443	Allow
Internet	App	Any	Deny
Internet	DB	Any	Deny
Web	App	App Port	Allow
Web	DB	DB Port	Deny
App	DB	DB Port	Allow

51 — Review Routing

Confirm:

Web Tier

Has required public routing.

Application Tier

Uses private routing and controlled outbound access where required.

Database Tier

Uses internal routes and no unnecessary public path.

52 — Review DNS

Confirm:

web.cloudplus.lab

app.cloudplus.lab

db.cloudplus.lab

resolve to the expected destinations within their intended scope.

53 — Review IAM

Confirm:

users use appropriate human identities
administrators use privileged controls
application uses workload identity
no developer credentials are embedded in the application

54 — Review Storage Security

Confirm:

storage remains private where required
encryption is enabled where appropriate
permissions are scoped
backups/recovery are considered

55 — Build the Complete Architecture

                              Internet
                                 |
                              HTTPS
                                 |
                                 v
                       +------------------+
                       | Web Tier         |
                       | Public Subnet    |
                       | 10.10.10.0/24    |
                       +------------------+
                                 |
                          Application Port
                                 |
                                 v
                       +------------------+
                       | Application Tier |
                       | Private Subnet   |
                       | 10.10.20.0/24    |
                       +------------------+
                          |             |
                          |             |
                    DB Port             | Workload Identity
                          |             |
                          v             v
                +----------------+   Object Storage
                | Database Tier  |
                | Private Subnet |
                | 10.10.30.0/24  |
                +----------------+

56 — Understand Failure Domains

Your current lab may contain:

One Web VM

One App VM

One DB

This is useful for learning but does not provide strong high availability.

🧠 Single Point of Failure

If:

Web VM
 ↓
FAILS

the application may become unavailable.

Later labs will address:

load balancing
auto scaling
high availability

57 — Understand Vertical vs Horizontal Application Scaling

Vertical:

Web VM
 ↓
Bigger Web VM

Horizontal:

Web VM 1
+
Web VM 2
+
Web VM 3

Three-tier architecture makes independent scaling easier.

58 — Identify Tier Scaling Requirements

Example:

Web Tier
High User Traffic
      ↓
Scale Horizontally

Application Tier
Heavy Processing
      ↓
Scale Independently

Database Tier
Storage / Query Constraints
      ↓
Database-Specific Scaling

59 — Understand Tier-Specific Monitoring

Each tier needs different telemetry.

Web:

request latency
HTTP errors
CPU
traffic

Application:

application errors
processing latency
dependencies

Database:

query performance
connections
storage
database health

60 — Create a Monitoring Requirement Matrix

Tier	Metric / Signal
Web	HTTP Errors
Web	Request Latency
App	Application Errors
App	Processing Time
DB	Connections
DB	Storage Usage
DB	Query Health

You will implement deeper monitoring later.

61 — Perform End-to-End Validation

Validate the complete path.

Client
 ↓
Web
 ↓
Application
 ↓
Database
 ↓
Response

62 — Record the Validation

Web Access:
Pass / Fail

Web → App:
Pass / Fail

App → DB:
Pass / Fail

Web → DB:
Blocked / Unexpected

Internet → App:
Blocked / Unexpected

Internet → DB:
Blocked / Unexpected

63 — Deliberately Break Web-to-App Connectivity

In the isolated lab, temporarily remove the required application-tier network rule.

Expected:

Web
 ↓
Application
 ↓
FAIL

64 — Observe User Impact

The web tier may remain:

Reachable

while the application function fails.

This teaches an important lesson:

A healthy web server does not prove the entire application is healthy.

65 — Troubleshoot the Failure

Use:

Web Service
    ↓
Application DNS
    ↓
Application IP
    ↓
Route
    ↓
Security Rule
    ↓
Application Listener

66 — Restore the Rule

Restore the required:

Web
 ↓
Application Port
 ↓
Application

Validate the application again.

67 — Deliberately Break Application-to-Database Connectivity

Temporarily remove the required app-to-database rule.

Expected:

Web
 ✓
 ↓
Application
 ✓
 ↓
Database
 ✗

🧠 Important

This is a classic multi-tier troubleshooting scenario.

The visible application may fail even though:

web server is running
application service is running

because a backend dependency has failed.

68 — Troubleshoot the Database Path

Use:

Application
    ↓
DB DNS
    ↓
DB IP
    ↓
Route
    ↓
Security Rule
    ↓
Database Listener
    ↓
Database Authentication

69 — Restore Database Connectivity

Restore the required app-to-db rule.

Validate the end-to-end application again.

70 — Deliberately Break DNS

Temporarily modify:

app.cloudplus.lab

to an incorrect lab address.

Observe the resulting failure.

71 — Troubleshoot DNS

Use:

Hostname
 ↓
Resolver
 ↓
Record
 ↓
Returned IP
 ↓
Expected IP

Restore the correct record afterward.

72 — Deliberately Stop the Application VM

Stop:

cloudplus-lab-app-01

Observe what happens to the end-to-end application.

73 — Troubleshoot the Compute Failure

Your path now becomes:

DNS
 ✓
Route
 ✓
Security
 ✓
Application VM
 ✗

🧠 Troubleshooting Lesson

Not every connectivity failure is:

network related.

74 — Restart the Application VM

Validate:

VM health
application process
application port
web-to-app communication

75 — Understand Service Startup Dependencies

A VM may start successfully while the application remains stopped.

Check:

VM Running
      ↓
Operating System Healthy
      ↓
Application Service Running?

76 — Build the Multi-Tier Troubleshooting Framework

Use:

Client
 ↓
DNS
 ↓
Web Tier
 ↓
Web Security
 ↓
App DNS
 ↓
App Tier
 ↓
App Security
 ↓
DB DNS
 ↓
DB Tier
 ↓
Database Service
 ↓
Response

77 — Use Dependency-Based Troubleshooting

Instead of asking:

Why is the application down?

Break the problem into:

Can Client Reach Web?

Can Web Reach App?

Can App Reach DB?

Can DB Process Request?

Possible architecture:

Web
 ✓

Application
 ?

Database
 ?

Do not assume the web server is the root cause.

79 — Troubleshooting Scenario — Web Shows 502/Backend Error

Investigate:

application DNS
route
security rule
application service
application health

80 — Troubleshooting Scenario — Application Reports Database Timeout

Investigate:

DB DNS
 ↓
Network
 ↓
Security
 ↓
Listener
 ↓
Database Health

81 — Troubleshooting Scenario — Web Can Access Database Directly

This may indicate:

excessive network permissions.

Review the architecture and remove unnecessary direct access.

82 — Troubleshooting Scenario — Application VM Has Public IP

Ask:

Is direct public access required?

If no:

remove public exposure
maintain controlled administration
validate outbound requirements separately

83 — Troubleshooting Scenario — Database Has Public IP

Treat this as a significant architecture review item unless explicitly required.

Review:

public IP
routing
security rules
workload requirement

84 — Troubleshooting Scenario — Application Uses Developer Credentials

Replace:

Application
      ↓
Developer Credentials

with:

Application
      ↓
Workload Identity
      ↓
Scoped Role

85 — Troubleshooting Scenario — Everything Works Using IP but Fails Using Name

Focus on:

DNS.

86 — Troubleshooting Scenario — DNS Resolves but Connection Fails

Move down the stack:

DNS
 ✓
 ↓
Route
 ↓
Security
 ↓
Service

87 — Perform a Three-Tier Security Assessment

Review:

[ ] Only required public services exposed
[ ] Application tier private
[ ] Database tier private
[ ] Web → App limited to required port
[ ] App → DB limited to required port
[ ] Web → DB blocked
[ ] Administrative access controlled
[ ] Workload identity used
[ ] Static cloud credentials avoided
[ ] Storage access scoped
[ ] DNS uses intended private names
[ ] Logging and monitoring considered

88 — Perform an Architecture Review

Ask:

Exposure

Which resources are publicly reachable?

Identity

Which identities can manage the environment?

Workload IAM

Which resources can the application access?

Data

Where is application data stored?

Availability

Which components are single points of failure?

Operations

How would the environment be monitored?

89 — Identify Current Single Points of Failure

Your lab may currently contain:

Component	Single Point of Failure?
Web VM	Yes
App VM	Yes
DB VM	Yes
Single Network Path	Review

🧠 Important

Three-tier architecture provides:

separation

but not automatically:

high availability.

90 — Create an Improvement Roadmap

Your next architecture improvements might include:

Load Balancer
      ↓
Multiple Web Servers
      ↓
Auto Scaling
      ↓
Multiple Failure Domains
      ↓
Highly Available Database

These are exactly what the next labs will introduce.

91 — Create the Final Architecture Documentation

Document:

Application:
CompTIA Cloud+ Three-Tier Lab

Network:
10.10.0.0/16

Web Tier:
10.10.10.0/24

Application Tier:
10.10.20.0/24

Database Tier:
10.10.30.0/24

Web DNS:
web.cloudplus.lab

Application DNS:
app.cloudplus.lab

Database DNS:
db.cloudplus.lab

Workload Identity:
cloudplus-app-identity

Public Exposure:
Web Only

Application Exposure:
Private

Database Exposure:
Private

92 — Create the Application Dependency Map

User
  ↓
DNS
  ↓
Web Service
  ↓
Application DNS
  ↓
Application Service
  ↓
Database DNS
  ↓
Database Service
  ↓
Persistent Storage

93 — Create the Security Architecture Record

Internet → Web:
HTTPS Only

Internet → App:
Denied

Internet → Database:
Denied

Web → App:
Required Application Port

Web → Database:
Denied

App → Database:
Required Database Port

Application → Storage:
Scoped Workload Identity

94 — Update the Resource Inventory

Resource	Tier	Network	Purpose	Status
cloudplus-lab-web-01	Web	Public	Presentation	Active
cloudplus-lab-app-01	App	Private App	Business Logic	Active
cloudplus-lab-db-01	Data	Private DB	Database	Active
cloudplus-app-identity	App	IAM	Workload Access	Active

95 — Capture Evidence

Capture sanitized evidence of:

three-tier network architecture
web workload
application workload
database workload
security-group rules
DNS records
workload identity
successful web-to-app test
successful app-to-db test
denied web-to-db test
broken-dependency troubleshooting

Do not include:

passwords
database credentials
access keys
private keys
tokens
MFA secrets

96 — Create the Lab Report

Use:

Lab:
Build a Three-Tier Cloud Application Architecture

Architecture:

Web Tier:

Application Tier:

Database Tier:

Network Design:

Traffic Flows:

DNS:

IAM:

Workload Identity:

Storage:

Security Controls:

Validation:

Failure Tests:

Root Causes:

Remediation:

Architecture Improvements:

Lessons Learned:

🧪 Final Validation Checklist

Validation	Status
Web tier deployed
Application tier deployed
Database tier deployed
Web placed in public subnet
App placed in private app subnet
DB placed in private DB subnet
Web service operational
App service operational
Database service operational
Web DNS configured
App DNS configured
DB DNS configured
Internet-to-web works
Internet-to-app blocked
Internet-to-db blocked
Web-to-app works
Web-to-db blocked
App-to-db works
Workload identity assigned
Storage access scoped
Static credentials avoided
Broken web-to-app path tested
Broken app-to-db path tested
DNS failure tested
Compute failure tested
Architecture documented
Security review completed
Availability gaps identified

97 — Cleanup Decision

If you are continuing with the next labs, retain the three-tier environment.

It will become the foundation for:

load balancing
auto scaling
high availability
monitoring
logging
alerting

Keep:

Virtual Network

Public Subnet

Application Subnet

Database Subnet

Security Groups

DNS Records

Web Tier

Application Tier

Database Tier

Workload Identity

Review any billable database or compute resources before leaving the environment idle.

Stop or remove unnecessary resources where appropriate.

🎯 Certification Connection

A Cloud+ scenario may say:

An internet-facing application server can communicate directly with a database containing sensitive information.

Think:

segmentation and tier separation.

Another:

The application tier needs to access a database but should not be reachable directly from the internet.

Think:

Private Application Subnet
      +
App → DB Access
      +
No Direct Internet Inbound

Another:

An application uses hard-coded infrastructure addresses.

Think:

DNS/service naming.

Another:

The web page loads but requests requiring application logic fail.

Think:

check the web-to-application dependency.

🎤 Interview Questions

Practice without notes.

1. What is a three-tier architecture?

2. What are the three tiers?

3. What does the web tier do?

4. What does the application tier do?

5. What does the data tier do?

6. Why separate these tiers?

7. Which tier normally requires public internet access?

8. Why should the application tier normally be private?

9. Why should the database tier normally be private?

10. Why should web servers not normally communicate directly with databases?

11. How would you secure communication between tiers?

12. How does DNS help a multi-tier application?

13. Why use workload identities?

14. Why avoid hard-coded cloud credentials?

15. What is a dependency in a cloud application?

16. How would you troubleshoot a three-tier application?

17. What does it mean if the web server is healthy but the application is unavailable?

18. Does three-tier architecture automatically provide high availability?

19. How would you scale the web tier?

20. How would you improve availability of this architecture?

🚨 Scenario Interview Question 1

Users can access the website, but application requests fail.

Investigate:

Web
 ✓
 ↓
App DNS
 ↓
Route
 ↓
Security
 ↓
Application Service

🚨 Scenario Interview Question 2

The application can reach the database by IP but not by hostname.

Focus on:

DNS.

🚨 Scenario Interview Question 3

The database hostname resolves correctly, but the application cannot connect.

Check:

Route
 ↓
Security Rule
 ↓
Host Firewall
 ↓
Database Listener
 ↓
Database Authentication

🚨 Scenario Interview Question 4

A database VM has a public IP because administrators find it easier to manage.

A stronger architecture would use:

Administrator
      ↓
Controlled Management Path
      ↓
Private Database

rather than unnecessary public exposure.

🚨 Scenario Interview Question 5

The web server has direct database access even though the architecture uses an application tier.

Review whether that access is actually necessary.

If not:

remove it.

🚨 Scenario Interview Question 6

A web VM fails and the entire application becomes unavailable.

This identifies:

a single point of failure.

Possible improvement:

Load Balancer
      ↓
Multiple Web Servers

🚨 Scenario Interview Question 7

Application demand increases, but database demand remains stable.

A three-tier architecture allows:

scaling the application tier independently.

🚨 Scenario Interview Question 8

A developer stores cloud-storage credentials in the application configuration.

Replace the pattern with:

Application
      ↓
Workload Identity
      ↓
Scoped Permission

🚨 Scenario Interview Question 9

Management asks why three servers are better than putting everything on one VM.

Explain:

separation of concerns
independent scaling
reduced blast radius
clearer access control
easier troubleshooting
better availability design options

🚨 Scenario Interview Question 10

A user reports “the cloud application is down.”

Do not immediately restart every server.

Troubleshoot dependencies:

Client
 ↓
DNS
 ↓
Web
 ↓
Application
 ↓
Database
 ↓
Storage

🧠 Three-Tier Interview Framework

Use:

User
 ↓
DNS
 ↓
Web Tier
 ↓
Network Security
 ↓
Application Tier
 ↓
Workload Identity
 ↓
Database Tier
 ↓
Storage
 ↓
Monitoring

💬 Interview Tip

Avoid:

“I would create three VMs: one web, one app, and one database.”

A stronger answer is:

“I would first define the application’s communication requirements and trust boundaries. I would place the web tier in a controlled public-facing network, keep application and database tiers private, allow only required tier-to-tier traffic, use private DNS instead of hard-coded addresses, use dedicated workload identities for cloud-resource access, protect data with appropriate storage controls, and validate both expected communication and denied paths. I would then identify single points of failure and design the next stage for load balancing and high availability.”

That demonstrates Cloud Engineer and Solutions Architect thinking.

📁 Portfolio Deliverables

Keep sanitized versions of:

1. Three-Tier Architecture Diagram

Show:

Internet
 ↓
Web
 ↓
Application
 ↓
Database

2. Network Segmentation Diagram

Document:

Public
 ↓
Private Application
 ↓
Private Database

3. Traffic-Flow Matrix

Document:

source
destination
protocol
port
expected action

4. DNS Architecture

Show:

web.cloudplus.lab

app.cloudplus.lab

db.cloudplus.lab

5. Workload Identity Architecture

Show:

Application
      ↓
Workload Identity
      ↓
Scoped Storage

6. Troubleshooting Case

Document one complete dependency failure:

Failure
 ↓
Evidence
 ↓
Dependency Identified
 ↓
Root Cause
 ↓
Remediation
 ↓
Validation

7. Architecture Review

Document:

security strengths
single points of failure
scalability limitations
recommended improvements

📝 Resume Examples

Instead of:

Built a three-tier cloud application.

Use:

Designed and deployed a segmented three-tier cloud application architecture with public web, private application, and private database tiers using controlled routing, least-privilege network access, private DNS, workload identities, and scoped storage permissions.

Or:

Validated end-to-end cloud application dependencies across DNS, web, application, database, IAM, routing, and security controls while troubleshooting deliberately introduced tier-to-tier failures.

Or:

Performed cloud architecture and security reviews identifying unnecessary exposure, cross-tier access, workload identity risks, and single points of failure with prioritized remediation recommendations.

⭐ Job-Readiness Check

You should now be able to:

explain three-tier architecture
identify web, app, and data tiers
place workloads in appropriate subnets
distinguish public and private tiers
define tier-to-tier communication
configure least-privilege network access
use DNS between application tiers
use workload identity
avoid hard-coded cloud credentials
secure storage access
explain application dependencies
validate end-to-end traffic
troubleshoot web-to-app failures
troubleshoot app-to-db failures
distinguish DNS from network failures
identify single points of failure
explain how the architecture can be scaled
perform a basic architecture review

🏆 Mission Complete

You have now moved from individual cloud components to:

Complete Cloud Application
      ↓
Web Tier
      ↓
Application Tier
      ↓
Database Tier

Your cloud environment now combines:

Compute
+
Networking
+
Routing
+
Security
+
DNS
+
Storage
+
IAM
+
Workload Identity
+
Application Architecture

The key lesson from this lab is:

Cloud architecture is about designing how components interact—not simply deploying resources. Strong designs control exposure, isolate responsibilities, use identity intentionally, protect data, and make dependencies understandable.

🚀 What’s Next?

Your current web tier still depends on a single web workload.

That creates:

a single point of failure.

The next lab introduces cloud load balancing.

You will move from:

                 User
                   ↓
                Web VM

to:

                 User
                   ↓
              Load Balancer
               /         \
              ↓           ↓
          Web VM 1     Web VM 2

You will work with:

frontend listeners
backend pools
multiple web servers
health checks
traffic distribution
security groups
DNS integration
unhealthy backend detection
backend failure simulation
load-balancer troubleshooting
availability concepts

➡️ Next: Lab 13 — Cloud Load Balancing Lab