Software Architecture: visual lecture notes

Description

These are the revised and illustrated notes of the Software Architecture lecture of the Master in Software and Data Engineering held at the Software Institute at USI Lugano, Switzerland during the Spring of 2023. The book includes the script for these lectures: Introduction Quality Attributes Definitions Modeling Software Architecture Modularity and Components Reusability and Interfaces Composability and Connectors Compatibility and Coupling Deployability, Portability and Containers Scalability Availability and Services Flexibility and Microservices Preface Acknowledgements Introduction De Architectura The Art and Science of Building Foundation Platforms Closed Open Interfaces Forces When do you need an architect? How Large? Software Architecture Lecture Context Why Software Architecture? Hiding Complexity Abstraction Communication Representation Visualization Quality Change Evolution Quality Attributes Quality Functional, Extra-Functional Qualities Internal vs. External Static vs. Dynamic Meta-Qualities Quality Attributes Design Qualities Feasibility Affordability Slack Time to Market Modularity Reusability Design Consistency Simplicity Complexity Clarity Stability Composability Deployability Normal Operation Qualities Performance Scalability Capacity Usability Ease of Support Serviceability Visibility Dependability Qualities Reliability Availability Security Qualities Defensibility, Survivability Privacy Change Qualities Flexibility Configurability Customizability Resilience, Adaptability Extensibility, Modifiability Elasticity Compatibility Portability Interoperability Ease of Integration Long Term Qualities Durability Maintainability Types of Maintenance Sustainability Definitions Who is a software architect? Functional Organization Cross-Functional Organization Facilitate Communication Software Engineering Lead Technology Expert Risk Management Architect Tribes Software Architecture and the Software Development Lifecycle Bridge the Gap Think Outside the Box Evolutionary Model Agile Unified Process System Lifecycle Defining Software Architecture Architecture vs. Code Architecture vs. Technology Architecture vs. Design Basic Definition Design Decisions Design Process Design Decisions Decision Making Phases Decision Trees Design Outcome Modeling Architecture Can this skeleton fly? Prescriptive vs. Descriptive Architecture Green Field Development Brown Field Development Architectural Degradation Causes of Architectural Drift From Drift to Erosion Entropy Architecture or Code First? Architecture Hoisting Presumptive vs. Reference Solution vs. Product M-Architecture vs. T-Architecture The $10000 boolean flag Art or Science? Science or Art? References Modeling Capturing the Architecture What is modeling? Abstraction and Interpretation Solving Problems with Models Question first, Model second Scope of the Model What is a view? How many views? Multiple Views View Consistency Domain and Design Models Modeling = Learning Domain Model Example Domain Model Design Model Example Design Model (Interfaces) Example Design Model (Implementation) Some Modeling Notations Use Case Scenarios Example Music Player Scenarios Feature Models Feature Model Example Feature Model Constraints Constrained Feature Model Example Feature Configuration From C4 to C5 System Context View System Context View Example Containers View Container View Example Example Containers Components View Components View Example C4 Classes View C5 Connectors View Connectors View Example 4+1 Logical View Logical View Notation Example Logical View Process View Example Process View Development View Example Development View Physical View Example Deployment View Content is more important than representation Model Quality Accuracy vs. Precision Model Quality - Advice Model-Driven Architecture References Modularity and Components What is a Software Component? Hardware Component Software Component Examples: Application-specific Components Examples: Infrastructure Components Black Box Recursive Components Clustering Components Design vs. Run-time Distributed Components Component Lifecycle Decisions Externally Sourced Components Discovery Selection Integration Test Release Deploy Stateful Components Migration Backup and Recovery Properties of Components Component Roles Stateless vs. Stateful Stateless vs. Stateful Code Stateless vs. Stateful Operations Components vs. Objects Component Technology Component Frameworks Component Frameworks Demo Videos Where to find components? Buy vs. Build How much does it cost? References Reusability and Interfaces Interfaces Component Interface Provided Interface Provided Interfacesand Component Roles Required Interface Explicit Interfaces Principle Information Hiding Effective Encapsulation Example Describing Interfaces Principle of Least Surprise Easy to use? Interface Description Languages Java/RMI C/RPC RAML OpenAPI/Swagger Working With IDL API Documentation Demo Videos What is an API? Is it really API? Many Applications Developers, Developers, Developers Where to find APIs? Operating Systems Programming Languages Hardware Access User Interfaces Databases Web Services API Design Where is the API? API Design: Where to start? Who to please? Reusable Interfaces Usability vs. Reusability Easy to reuse? Performance vs. Reusability Small Interfaces Principle How many clients can these APIs satisfy? Uniform Access Principle Few Interfaces Principle Clear Interfaces Principle Let's create a new Window Expressive? No: Stringly Typed Consistent? Primitive Operations Design Advice References Composability and Connectors Software Connectors Connector: enabler of composition Software Connector Components vs. Connectors Connectors are Abstractions Connector Roles and Runtime Qualities Connectors and Transparency Connector Cardinality Connectors and Distribution Connectors and Availability Software Connector Examples RPC: Remote Procedure Call File Transfer Shared Database Message Bus Stream Linkage Shared Memory Disruptor Tuple Space Web Blockchain References Compatibility and Coupling Compatibility Compatible Interfaces There's an app adapter for that! Adapter Wrapper Mismatch Example Partial Wrappers Types of Interface Mismatches Synchronous vs. Asynchronous Interfaces Half-Sync/Half-Async Sync to Async Adapter Half-Async/Half-Sync Async to Sync Adapter How many Adapters? Scaling Adapters with N Interfaces Composing Adapters One or Two Adapters? Reusable Adapters and Performance How Standards Proliferate On Standards Standard Software Interfaces Representation Formats Operations Protocols Addressing Interface Description Coupling Understanding Coupling Coupling Facets Session Coupling Examples Binding Times Be liberal in what you accept, and conservative in what you send. Water or Gas Pipe? References Deployability, Portability and Containers The Age of Continuity Deployability Metrics Release Release Frequency Speed vs. Quality Software Production Pipeline High Quality at High Speed Types of Testing Types of Release Gradual Phase-In Essential Continuous Engineering Practices Tools Build Pipeline Demo Videos Container Orchestration Demo Videos Virtualization and Containers Virtualization Lightweight Virtualization with Containers VM vs. Container Containers inside VMs Images and Snapshots Virtual Machine Migration Inverted Hypervisor Virtual Hardware = Software References Scalability Will it scale? Scalability and Workload Scalability and Workload: Centralized How to scale? Scalability and Resources: Decentralized Scalability and Resources Centralized or Decentralized? Scalability at Scale Scale Up or Scale Out? Scaling Dimensions Scalability Patterns Directory Dependency Injection Directory vs. Dependency Injection Scatter/Gather Master/Worker Master Responsibilities Worker Responsibilities Load Balancing Variants Sharding Computing the Shard Key Looking up the Shard Key References Availability and Services Components vs. Services Business model: how to sell Design decisions Technology: how to use Availability Availability Questions Monitoring Availability Which kind of monitor? Availability Incidents Downtime Impact Contain Failure Impact Retry Circuit Breaker Canary Call Redundancy State Replication Which kind of replication? CAP Theorem CAP Theorem Proof Eventual Consistency Event Sourcing References Flexibility and Microservices API Evolution Only one chance... API Evolution API Compatibility Semantic Versioning Changes and the Build Pipeline Version Identifier Two in Production API Sunrise and Sunset To break or not to break Who should keep it compatible? Layers Layering Examples Data on the Inside, Data on the Outside Tolerant Reader Which kind of reader? Extensibility Extensibility and Plugins Microservices Monolith vs. Microservices Will this component always terminate? Will this service run forever? Will this microservice continuously change? DevOps DevOps Requirements Feature Toggles How small is a Microservice? Continuous Evolution Hexagon Model Decomposition Independent DevOps Lifecycle Isolated Microservices Splitting the Monolith Microservice Best Practices Bezos's Mandate (2002) Evans's Bounded Context (2004) Bob Martin's Single Responsibility Principle (2003) UNIX Philosophy (1978) Separation of Concerns (1974) Parnas's Criteria (1971) Conway's Law (1968) Vogels's Lesson (2006) References