When to use microservices (and when not to) - Architecture Diagram

System Overview - When to use microservices (and when not to)

This system explains when to choose microservices architecture versus when to avoid it. Microservices break a large application into smaller, independent services that communicate over a network. The key requirements are scalability, independent deployment, and fault isolation for complex systems. However, for simple or small applications, microservices may add unnecessary complexity.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +---------------------+---------------------+
  |                     |                     |
Service A           Service B             Service C
  |                     |                     |
Database A          Database B            Database C
  |                     |                     |
Cache A             Cache B               Cache C

Components

User

user

End user interacting with the system

Load Balancer

load_balancer

Distributes incoming requests evenly across API Gateway instances

API Gateway

api_gateway

Routes requests to appropriate microservices and handles authentication

Service A

microservice

Handles a specific business capability independently

Service B

microservice

Handles another distinct business capability independently

Service C

microservice

Handles a third business capability independently

Database A

database

Stores data for Service A

Database B

database

Stores data for Service B

Database C

database

Stores data for Service C

Cache A

cache

Speeds up data access for Service A

Cache B

cache

Speeds up data access for Service B

Cache C

cache

Speeds up data access for Service C

Request Flow - 10 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Service A

Service A → Cache A

Cache A → Service A

Service A → Database A

Database A → Service A

Service A → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Database B

Impact:Service B cannot read or write data, causing failures in that business capability. Other services remain unaffected.

Mitigation:Use database replication and failover to a standby database. Service B can serve stale data from cache if available. Alerting and retries help recover.

Architecture Quiz - 3 Questions

Which component directs user requests to the correct microservice?

A Load Balancer

B API Gateway

C Cache

D Database

Design Principle

This architecture shows how microservices enable independent scaling and fault isolation by splitting a system into smaller services with dedicated databases and caches. It also highlights the importance of API Gateway and Load Balancer for routing and load distribution. Microservices add complexity, so they are best for complex systems, not simple ones.

Practice

1. Which scenario is best suited for using microservices architecture?

easy

A. A large, complex application requiring independent scaling of components

B. A simple, single-function app with a small user base

C. A small script running on a single machine

D. A static website with no backend logic

Solution

1. Step 1: Understand microservices purpose

   Microservices are designed for complex apps where parts can scale or update independently.

2. Step 2: Match scenario to microservices benefits

   A large app needing flexibility and scaling fits microservices well; small or simple apps do not.

3. Final Answer:

   A large, complex application requiring independent scaling of components -> Option A

4. Quick Check:

   Complex app = microservices [OK]

Hint: Use microservices only for complex, scalable apps [OK]

Common Mistakes:

• Choosing microservices for small or simple apps
• Ignoring team size and management overhead
• Assuming microservices always improve performance

2. Which of the following is a correct reason NOT to use microservices?

easy

A. The app requires frequent updates to parts

B. The application is very small and simple

C. The app needs to scale independently

D. The app has multiple teams working on different features

Solution

1. Step 1: Identify when microservices are unnecessary

   Microservices add complexity and overhead, so small simple apps don't benefit.

2. Step 2: Evaluate options

   Options A, B, and D are reasons to use microservices, not avoid them.

3. Final Answer:

   The application is very small and simple -> Option B

4. Quick Check:

   Small app = avoid microservices [OK]

Hint: Avoid microservices for small, simple apps [OK]

Common Mistakes:

• Confusing scaling needs as a reason to avoid microservices
• Ignoring complexity added by microservices
• Assuming microservices fit all team sizes

3. Consider a microservices app with 5 services. If each service requires 2 developers and the team has only 6 developers total, what is the likely outcome?

medium

A. The team can easily manage all services independently

B. The services will merge into a monolith automatically

C. The team will struggle due to insufficient resources for each service

D. The app will automatically scale without developer input

Solution

1. Step 1: Calculate developer needs

   5 services x 2 developers each = 10 developers needed.

2. Step 2: Compare with available team size

   Only 6 developers are available, which is less than 10, causing resource strain.

3. Final Answer:

   The team will struggle due to insufficient resources for each service -> Option C

4. Quick Check:

   Dev shortage = struggle managing microservices [OK]

Hint: Check if team size matches microservices needs [OK]

Common Mistakes:

• Assuming microservices scale developer needs automatically
• Ignoring team size constraints
• Thinking services merge automatically without effort

4. A team tries to convert a small monolithic app into microservices but faces deployment failures and communication errors. What is the most likely cause?

medium

A. Microservices do not support deployment automation

B. The app was too large for microservices

C. They used too many developers

D. They underestimated the complexity of managing microservices

Solution

1. Step 1: Analyze the problem context

   Small apps converted to microservices often face complexity in communication and deployment.

2. Step 2: Identify the cause

   Deployment failures and communication errors usually come from underestimating microservices management overhead.

3. Final Answer:

   They underestimated the complexity of managing microservices -> Option D

4. Quick Check:

   Underestimating complexity = deployment issues [OK]

Hint: Expect extra management work with microservices [OK]

Common Mistakes:

• Blaming microservices for deployment automation lack
• Assuming more developers cause deployment errors
• Thinking large apps cause these specific errors

5. A startup with a small team plans to build a new app. They want to decide between microservices and a monolithic design. Which approach should they choose and why?

hard

A. Start with a monolith to reduce complexity and switch later if needed

B. Start with microservices to prepare for future scaling immediately

C. Use microservices only if the app is a static website

D. Avoid both and build multiple separate apps

Solution

1. Step 1: Consider team size and app complexity

   A small team benefits from simpler monolithic design to reduce overhead and speed development.

2. Step 2: Plan for future growth

   Starting monolithic allows easier initial development; microservices can be adopted later if scaling is needed.

3. Final Answer:

   Start with a monolith to reduce complexity and switch later if needed -> Option A

4. Quick Check:

   Small team = start monolith [OK]

Hint: Small teams start monolith, scale to microservices later [OK]

Common Mistakes:

• Choosing microservices too early for small teams
• Confusing static websites with microservices use
• Ignoring future scalability planning