System Architecture Overview

System architecture defines the structure of a software system, the relationships among its components, and the principles guiding its design and evolution.

Core concepts

• Components — deployable units that encapsulate behavior (services, databases, queues).
• Interfaces — contracts that define how components interact.
• Quality attributes — non-functional requirements such as availability, scalability, and security.
• Constraints — limitations imposed by technology, budget, regulation, or organizational boundaries.
• Trade-offs — deliberate choices between competing quality attributes.

Common architecture patterns

Pattern	Use case	Trade-off
Layered (n-tier)	Enterprise applications	Can become rigid at scale.
Microservices	Independent team ownership	Adds operational complexity.
Event-driven	Asynchronous workflows	Requires robust observability.
Serverless	Variable or infrequent workloads	Cold starts and vendor lock-in.
Circuit breaker	Resilient external calls	Adds latency and tuning overhead.

Key quality attributes

Attribute	Concern
Availability	Uptime and fault tolerance.
Scalability	Handling growth in load or data.
Maintainability	Ease of change and testing.
Security	Protection against threats.
Observability	Ability to diagnose behavior in production.
Performance	Response time and throughput.

Architecture Decision Record (ADR) template

Use the following structure when documenting significant decisions:

1. Title — short name and date.
2. Context — forces and constraints that require a decision.
3. Decision — the chosen option.
4. Consequences — positive and negative outcomes.
5. Status — proposed, accepted, deprecated, or superseded.

Best practices

• Design for failure rather than assuming perfect conditions.
• Prefer simplicity until complexity is justified by measured need.
• Document decisions with ADRs so future teams understand intent.
• Validate architecture with prototypes, load tests, and chaos experiments.