Mini Projects
These mini-projects have been verified as an effective approach to mastering system design interviews through practical implementation. Each project addresses core concepts directly relevant to common interview questions while helping you develop both technical skills and architectural thinking.
Core Foundations Projects
1. Multi-Protocol API Gateway
Description: Build a simple API gateway that handles requests in multiple formats (REST, GraphQL) and routes them to appropriate backend services.
Key Concepts:
- API Gateway architecture
- Protocol translation
- Request routing
- Basic authentication and rate limiting
Implementation Guidelines:
- Use Node.js/Express, Spring Boot, or similar frameworks
- Implement at least two different backend services
- Support both RESTful and GraphQL interfaces
- Add basic rate limiting and authentication
Learning Outcomes: Understanding API gateway patterns, protocol transformation, and cross-cutting concerns in distributed systems.
2. Event-Driven Notification System
Description: Create a notification system using an event-driven architecture that can send notifications through multiple channels (email, SMS, push) when events occur.
Key Concepts:
- Event-driven architecture
- Asynchronous communication
- Message queues
- Publisher-subscriber pattern
Implementation Guidelines:
- Use Kafka, RabbitMQ, or similar message broker
- Implement event producers and multiple consumers
- Create adapters for different notification channels
- Design for fault tolerance and delivery guarantees
Learning Outcomes: Practical experience with event-driven systems, message brokers, and asynchronous processing patterns.
3. Polyglot Persistence Application
Description: Develop an application that uses different database types for different data needs within the same system.
Key Concepts:
- SQL and NoSQL database selection
- Data modeling for different databases
- Service integration with multiple data stores
- Appropriate data store selection
Implementation Guidelines:
- Use a relational database (PostgreSQL/MySQL) for structured data
- Implement a document store (MongoDB) for flexible schema data
- Add a key-value store (Redis) for caching
- Create a coherent application that uses each for appropriate data
Learning Outcomes: Understanding when to use different database technologies and how to integrate them in a single application.
4. Horizontal Scaling Simulator
Description: Build a simulation that demonstrates horizontal scaling concepts with virtual nodes that can be added/removed dynamically.
Key Concepts:
- Horizontal scaling (scaling out)
- Load balancing algorithms
- Health checks and service discovery
- Auto-scaling policies
Implementation Guidelines:
- Create virtual “service nodes” that process simulated requests
- Implement a load balancer with configurable algorithms
- Add auto-scaling logic based on load metrics
- Visualize the system performance as nodes are added/removed
Learning Outcomes: Deep understanding of scaling dynamics, load balancing strategies, and the practical challenges of distributed systems.
Performance and Reliability Projects
5. Multi-Layer Caching System
Description: Implement a system with multiple caching layers to optimize data access patterns for a read-heavy application.
Key Concepts:
- Cache hierarchies
- Cache eviction policies
- Cache invalidation strategies
- Write-through vs. write-behind caching
Implementation Guidelines:
- Create an API with database backend
- Add application-level caching (in-memory)
- Implement distributed caching layer (Redis)
- Add browser/client caching headers
- Measure and compare performance across scenarios
Learning Outcomes: Understanding of caching architectures, when to apply different caching strategies, and their performance impacts.
6. Resilient Microservice with Circuit Breaker
Description: Build a microservice that implements fault tolerance patterns to handle downstream service failures gracefully.
Key Concepts:
- Circuit breaker pattern
- Fallback mechanisms
- Timeout and retry strategies
- Bulkhead pattern
Implementation Guidelines:
- Create a service that depends on multiple downstream services
- Implement circuit breakers (using Hystrix, Resilience4j, or similar)
- Add intelligent retry logic with exponential backoff
- Develop fallback mechanisms for degraded service
- Create a dashboard showing circuit states
Learning Outcomes: Practical experience implementing fault tolerance patterns that prevent cascading failures in distributed systems.
7. Rate Limiter Implementation
Description: Design and implement different rate limiting algorithms to protect API resources from overuse.
Key Concepts:
- Token bucket algorithm
- Leaky bucket algorithm
- Fixed/sliding window counters
- Distributed rate limiting
Implementation Guidelines:
- Implement multiple rate limiting algorithms
- Create visualizations of how each algorithm behaves
- Support different rate limits for different resources
- Add distributed rate limiting using Redis
- Test with simulated traffic patterns
Learning Outcomes: Understanding rate limiting algorithms, their tradeoffs, and how they protect systems from excessive load.
8. Database Sharding Simulator
Description: Create a simulation that demonstrates different database sharding strategies and their effects on query performance.
Key Concepts:
- Horizontal sharding strategies
- Shard key selection
- Cross-shard queries
- Rebalancing and data migration
Implementation Guidelines:
- Build a simulated database with configurable sharding strategies
- Implement different sharding approaches (hash, range, directory)
- Create visualization of data distribution across shards
- Add querying capability to demonstrate cross-shard operations
- Simulate shard rebalancing operations
Learning Outcomes: Understanding the tradeoffs of different sharding approaches and their impact on scalability and query patterns.
Specialized System Components Projects
9. OAuth 2.0 Authorization Server
Description: Build a complete OAuth 2.0 authorization server that supports different grant types and integrates with a resource server.
Key Concepts:
- Authentication vs. authorization
- OAuth 2.0 flows
- JWT token generation and validation
- Scope-based permissions
Implementation Guidelines:
- Implement authorization code, client credentials, and refresh token flows
- Add JWT token generation with proper claims
- Create a resource server that validates tokens
- Implement scope-based authorization checks
- Add token revocation capability
Learning Outcomes: Deep understanding of OAuth 2.0, token-based authentication, and building secure API access controls.
10. Distributed Tracing System
Description: Create a lightweight distributed tracing implementation that can track requests across multiple services.
Key Concepts:
- Distributed tracing
- Context propagation
- Sampling strategies
- Trace visualization
Implementation Guidelines:
- Build a set of microservices with defined interactions
- Implement trace context generation and propagation
- Add span collection and recording
- Create a visualization dashboard for traces
- Support filtering and searching traces
Learning Outcomes: Understanding how distributed tracing works and how to implement context propagation across service boundaries.
11. Time Series Metrics Collection System
Description: Develop a system to collect, store, and visualize time series metrics from multiple sources.
Key Concepts:
- Time series data modeling
- Metrics collection
- Data downsampling
- Time series visualization
Implementation Guidelines:
- Create metrics collection agents
- Implement a time series database (or use InfluxDB/Prometheus)
- Add downsampling logic for historical data
- Build dashboards for metric visualization
- Implement alerting based on thresholds
Learning Outcomes: Experience with time series data patterns, efficient storage, and visualization of operational metrics.
12. Search Engine for Document Repository
Description: Build a search engine for a collection of documents with ranking, filtering, and suggestion capabilities.
Key Concepts:
- Inverted indexes
- Full-text search
- Relevance scoring
- Query expansion
Implementation Guidelines:
- Create an inverted index from a document collection
- Implement text analysis (tokenization, stemming)
- Add relevance scoring algorithm
- Support filters and faceted search
- Implement auto-complete suggestions
Learning Outcomes: Understanding search system architecture, indexing strategies, and relevance optimization.
13. Real-time Analytics Dashboard
Description: Create a real-time analytics system that processes streams of events and updates dashboards in real-time.
Key Concepts:
- Stream processing
- Real-time aggregations
- Windowing operations
- WebSocket communication
Implementation Guidelines:
- Generate or capture a stream of events
- Process events using windowing operations
- Compute real-time aggregations and metrics
- Push updates to clients via WebSockets
- Create interactive dashboards with live updates
Learning Outcomes: Understanding real-time analytics architecture, stream processing patterns, and client push technologies.
Cloud and Infrastructure Projects
14. Container Orchestration Mini-Platform
Description: Build a simplified container orchestration system that schedules and manages containerized applications.
Key Concepts:
- Container lifecycle management
- Resource allocation
- Service discovery
- Health checking
Implementation Guidelines:
- Create a scheduler for placing containers on nodes
- Implement service registration and discovery
- Add health checking and container restart logic
- Create a simple CLI for managing the platform
- Support basic networking between containers
Learning Outcomes: Understanding container orchestration principles and the challenges of distributed scheduling.
15. Serverless Function Platform
Description: Develop a lightweight serverless platform that can execute functions in response to events.
Key Concepts:
- Function-as-a-Service (FaaS)
- Event sourcing
- Cold start management
- Function isolation
Implementation Guidelines:
- Create an environment for running isolated functions
- Implement event triggers from multiple sources
- Add function scaling based on demand
- Create function logs and monitoring
- Support different runtimes (e.g., Node.js, Python)
Learning Outcomes: Understanding serverless architecture patterns, function isolation, and event-driven execution models.
16. Multi-Region Deployment Simulator
Description: Build a simulation of a multi-region application deployment with traffic routing and failover capabilities.
Key Concepts:
- Geographic load balancing
- Region failover strategies
- Latency-based routing
- Global state management
Implementation Guidelines:
- Simulate multiple regions with artificial latency
- Implement DNS-based routing between regions
- Add health checking and automated failover
- Create a global configuration management system
- Build dashboards showing traffic distribution
Learning Outcomes: Understanding global application deployment strategies, failover mechanisms, and geographic routing.
Testing and Evaluation Projects
17. Chaos Engineering Toolkit
Description: Create a toolkit for conducting chaos engineering experiments on distributed systems.
Key Concepts:
- Failure injection
- Chaos experiment design
- System observability
- Resilience testing
Implementation Guidelines:
- Implement different failure modes (latency, errors, resource exhaustion)
- Create an experiment runner with safety measures
- Add metrics collection to observe system behavior
- Build analysis tools to evaluate resilience
- Support scheduled and on-demand experiments
Learning Outcomes: Understanding chaos engineering principles and how to systematically test system resilience.
18. Performance Testing Framework
Description: Build a framework for load testing systems and analyzing performance bottlenecks.
Key Concepts:
- Load generation
- Performance metrics collection
- Bottleneck identification
- Resource utilization analysis
Implementation Guidelines:
- Create configurable load generation
- Implement distributed test agents
- Add metrics collection during tests
- Build visualization of performance results
- Support different test scenarios and patterns
Learning Outcomes: Understanding performance testing methodologies and how to identify system bottlenecks.
19. Contract Testing Implementation
Description: Develop a contract testing system to verify compatibility between microservices.
Key Concepts:
- Consumer-driven contracts
- API compatibility verification
- Service evolution patterns
- Integration testing
Implementation Guidelines:
- Create a contract definition language/format
- Implement contract verification for consumers
- Add provider contract validation
- Build a contract repository
- Support contract evolution and versioning
Learning Outcomes: Understanding how to use contract testing to ensure compatible service interactions in distributed systems.
20. System Design Evaluation Tool
Description: Create an interactive tool to evaluate system designs against various criteria like scalability, reliability, and cost.
Key Concepts:
- Architecture evaluation frameworks
- Trade-off analysis
- Capacity planning
- Cost modeling
Implementation Guidelines:
- Build a modeling tool for system components
- Implement evaluation against different criteria
- Add visualization of bottlenecks and limitations
- Support what-if analysis for different scenarios
- Include cost estimation for different architectures
Learning Outcomes: Understanding how to systematically evaluate system designs and make data-driven architecture decisions.
Recommended Approach for Each Project
For each mini-project, follow the “UNDER” method to structure your approach:
- Understanding the business domain: Clarify the problem space and requirements before starting implementation
- Narrowing the scope: Define clear boundaries for what your implementation will and won’t include
- Discovering numbers: Establish performance requirements and constraints for the system
- Evaluating basic design: Create an initial architecture and validate it against requirements
- Redesigning current architecture: Iteratively improve your implementation based on testing and feedback
Implementation Strategy
For optimal learning with each mini-project:
- Start Small: Begin with a minimal viable implementation focusing on the core concepts
- Iterate: Add complexity gradually as you master the basics
- Document: Keep notes on design decisions, challenges, and solutions
- Test Edge Cases: Deliberately create failure scenarios to test resilience
- Measure: Collect metrics to understand performance characteristics
- Visualize: Create diagrams that explain your architecture and implementation choices