design-document

name	design-document
description	Design document writing conventions. Use when writing or reviewing technical design documents.

Design Document Conventions

1. Background / Problem Statement

1.1 Background and Pain Points

• Describe current system/module limitations and deficiencies
• List specific scenarios, metrics, or incident cases that triggered this design

1.2 Impact Scope

• Affected modules, microservices, APIs, data stores, third-party dependencies
• Potential impact on performance, reliability, cost, maintainability
• Forward/backward compatibility analysis

1.3 Constraints

• Compliance/security/performance/resource restrictions
• External system or infrastructure dependencies

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2. Design Goals

2.1 Functional Goals

• List Must/Should/Could core capabilities by priority

2.2 Non-Functional Goals

• Performance (throughput, latency, concurrency, resource usage)
• Scalability, maintainability, testability, observability
• Reliability (fault tolerance, HA, degradation, rollback strategies)

2.3 Constraint Goals

• Backward compatibility, API stability
• Security and compliance requirements

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3. Technical Design

3.1 Architecture Diagram

• Use Mermaid for high-level component diagrams with data/control flow

3.2 Detailed Flowcharts

• Key business flows, exception flows, retry/compensation with timing and triggers

3.3 Thread/Concurrency Model

• Thread lifecycle, inter-thread communication (locks, condition variables, queues, Actor patterns)
• Sequence diagrams for concurrency interactions

3.4 Core Classes and Data Structures

• Class diagrams showing main classes, interfaces, inheritance/composition relationships
• Key data structure fields, lifecycle, thread-safety strategy

3.5 Key Algorithms or Protocols

• Pseudocode or flow for pub/sub, load balancing, retry backoff, etc.
• State machine / protocol state transition diagrams

3.6 Error Handling and Recovery

• Error classification, exception stack, retry strategies, degradation plans
• Monitoring metrics, alert trigger conditions and levels

3.7 Deployment and Operations

• Configuration items, hot-update mechanisms, canary and rollback strategies
• CI/CD, container, Service Mesh, Kubernetes resource considerations

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4. Unit Testing

4.1 Test Scope and Goals

• Cover core logic, boundary conditions, concurrency scenarios, exception paths

4.2 Test Environment and Tools

• Google Test/Mock version, necessary third-party stubs/fakes

4.3 Test Scenarios and Cases

Case ID	Scenario	Input	Expected Output/Behavior	Mock Dependencies
TC-01	Normal single log push	Single valid LogRecord	Returns SUCCESS, buffer size +1	None
TC-02	Buffer full	capacity=N filled	Throws BufferOverflowException	None
TC-03	Concurrent push	Multi-thread simultaneous push	No data loss, order/final consistency matches design	MutexMock
TC-04	flush clears	M items exist, then flush	Returns M items, buffer size=0	TimeProviderMock

4.4 Boundary and Exception Testing

• Empty input, invalid input, extreme capacity, network/disk fault injection

4.5 Performance Benchmarking (optional)

• Throughput, latency, CPU/Memory profile; comparison with baseline

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Notes

• Do not include project management info (estimates, schedules, milestones, Gantt charts)
• Code examples must follow team C++ coding standards (see .claude/skills/project-knowledge/)
• Test case naming: <Module>_<Function>_<Number> for CI coverage tracking