Multi-tier architecture patterns in AWS - Step-by-Step Execution

Process Flow - Multi-tier architecture patterns

User Request

↓

Presentation Tier

↓

Application Tier

↓

Data Tier

↓

Response to User

User requests go through layers: first the presentation, then application, then data, and back with a response.

Execution Sample

AWS

User -> ELB -> EC2 App Servers -> RDS Database

Shows a simple multi-tier flow: user request hits load balancer, then app servers, then database.

Process Table

Step	Component	Action	Input	Output
1	User	Sends request	User input	HTTP request to ELB
2	Elastic Load Balancer	Receives request	HTTP request	Forwards to App Server
3	App Server (EC2)	Processes request	Request data	Queries Database
4	RDS Database	Executes query	SQL query	Returns data
5	App Server (EC2)	Builds response	Database data	HTTP response
6	Elastic Load Balancer	Sends response	HTTP response	Response to User
7	User	Receives response	HTTP response	Displays content

💡 User receives response; request cycle completes.

Status Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	Final
Request	User input	At App Server	At App Server	At App Server (response)	At User (response)
Data	N/A	N/A	Database query result	Response built	Displayed content

Key Moments - 3 Insights

Why does the user request go through the load balancer before reaching the app servers?

The load balancer distributes incoming requests evenly to app servers for reliability and scalability, as shown in execution_table step 2.

What happens if the database is slow to respond?

The app server waits for the database query result before building the response, delaying steps 4 and 5 in the execution_table.

Can the user communicate directly with the database?

No, the user only interacts with the presentation tier; the database is accessed only by the application tier, as shown in steps 1 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the app server query the database?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check the 'Component' and 'Action' columns for database query.

According to variable_tracker, where is the request after step 4?

A At User

B At App Server

C At ELB

D At Database

💡 Hint

Look at the 'Request' row and the 'After Step 4' column.

If the load balancer is removed, what changes in the execution flow?

A User sends request directly to app servers

B Database receives requests directly

C App servers send responses to ELB

D User communicates directly with database

💡 Hint

Consider the role of ELB in step 2 of execution_table.

Concept Snapshot

Multi-tier architecture splits cloud apps into layers:
- Presentation tier handles user interface
- Application tier processes logic
- Data tier stores info
Requests flow through these tiers for scalability and security.

Full Transcript

Multi-tier architecture means splitting an application into layers: presentation, application, and data. The user sends a request that first hits the presentation tier, often a load balancer, which forwards it to application servers. These servers process the request and query the data tier, usually a database. The data is returned back through the layers to the user. This pattern helps keep the system organized, scalable, and secure by separating concerns and controlling access between layers.

Practice

1. What is the main purpose of using a multi-tier architecture in AWS?

easy

A. To combine all application components into a single server

B. To reduce the number of servers needed by merging databases and web servers

C. To separate an application into layers for better security and scalability

D. To allow direct internet access to all parts of the application

Solution

1. Step 1: Understand multi-tier architecture concept

   Multi-tier architecture divides an app into layers such as web, application, and database tiers.

2. Step 2: Identify benefits of layering

   This separation improves security by isolating layers and helps scale parts independently.

3. Final Answer:

   To separate an application into layers for better security and scalability -> Option C

4. Quick Check:

   Multi-tier = layers for security and scaling [OK]

Hint: Think layers for security and growth, not one big block [OK]

Common Mistakes:

• Thinking all parts should be on one server
• Assuming all components need internet access
• Confusing multi-tier with single-tier or monolithic

2. Which AWS subnet type is typically used to host internet-facing web servers in a multi-tier architecture?

easy

A. Public subnet

B. Isolated subnet

C. Private subnet

D. VPN subnet

Solution

1. Step 1: Recall subnet types in AWS

   Public subnets have a route to the internet gateway, allowing internet access.

2. Step 2: Match subnet to web servers

   Internet-facing web servers need public subnets to receive traffic from users.

3. Final Answer:

   Public subnet -> Option A

4. Quick Check:

   Internet-facing = public subnet [OK]

Hint: Public subnet means internet access for web servers [OK]

Common Mistakes:

• Choosing private subnet which blocks internet access
• Confusing isolated subnet with public
• Thinking VPN subnet is for public web servers

3. In a multi-tier AWS architecture, which tier is usually placed in a private subnet to protect sensitive data?

medium

A. Database tier

B. Application tier

C. Web tier

D. Load balancer tier

Solution

1. Step 1: Identify tiers and their security needs

   The database tier holds sensitive data and needs strong protection.

2. Step 2: Determine subnet placement

   Private subnets restrict internet access, ideal for databases to prevent direct exposure.

3. Final Answer:

   Database tier -> Option A

4. Quick Check:

   Database = private subnet for security [OK]

Hint: Sensitive data stays in private subnet (database) [OK]

Common Mistakes:

• Placing web tier in private subnet
• Assuming load balancer is in private subnet
• Confusing application tier with database tier

4. You deployed a multi-tier app but the application tier in the private subnet cannot connect to the database tier. What is the most likely cause?

medium

A. The load balancer is not configured

B. The web tier is in a public subnet

C. The application tier has a public IP address

D. The database security group does not allow inbound traffic from the application tier

Solution

1. Step 1: Analyze connectivity between application and database tiers

   Application tier must be allowed by database security group to connect on required ports.

2. Step 2: Check common misconfigurations

   If security group blocks inbound traffic, connection fails despite correct subnet placement.

3. Final Answer:

   The database security group does not allow inbound traffic from the application tier -> Option D

4. Quick Check:

   Security group rules control traffic between tiers [OK]

Hint: Check security group rules for inter-tier traffic [OK]

Common Mistakes:

• Blaming web tier subnet for app-db connection
• Assuming public IP needed for private subnet
• Ignoring security group inbound rules

5. You want to design a multi-tier AWS app with a public web tier, private application tier, and private database tier. Which setup best follows best practices?

hard

A. Place all tiers in public subnets with direct internet access for simplicity

B. Place web servers in public subnet with internet gateway; app and database servers in private subnets with NAT gateway for outbound internet

C. Place web and app tiers in private subnets; database in public subnet for easy access

D. Place web tier in private subnet; app and database tiers in public subnets

Solution

1. Step 1: Assign subnet types based on tier roles

   Web tier needs public subnet for user access; app and database tiers should be private for security.

2. Step 2: Provide outbound internet for private tiers

   Use NAT gateway so private tiers can access internet for updates without exposing them inbound.

3. Final Answer:

   Place web servers in public subnet with internet gateway; app and database servers in private subnets with NAT gateway for outbound internet -> Option B

4. Quick Check:

   Public web, private app/db, NAT for outbound [OK]

Hint: Public web, private app/db, NAT gateway outbound [OK]

Common Mistakes:

• Putting database in public subnet
• Giving private tiers direct internet access
• Mixing subnet roles incorrectly