Software Architecture Design and Patterns

Introduction to Software Architecture

Software architecture and design:

• Design and documentation take place during the design phase of the SDLC
• Software architecture is the organization of the system
• Serves as a blueprint for developers

• Comprised of fundamentals structures and behaviors

  Early design decisions:

• How components interact
• Operating environment
• Design principles
• Costly to change once implemented

• Addresses non-functional aspects

  Why software architecture is important:

• Communication
• Earliest design decisions
• Flexibility

• Increases lifespan

  Software architecture and tech stacks:

• Guides technology stack choice
• Tech stacks must address non-functional capabilities
• Tech stacks include:
  • Software
  • Programming languages
  • Libs
  • Frameworks
  • Architects must weigh advantages and disadvantages of tech stack choices

Artifacts

• Software design document (SDD)
• Architectural diagrams
• Unified modeling language (UML) diagrams

1. Software Design Document (SDD)
   • Collection of tech specs regarding design implementation
   • Design considerations:
   • Assumptions
   • Dependencies
   • Constraints
   • Requirements
   • Objectives
   • Methodologies
2. Architectural diagrams
   It displays:
   • Components
   • Interactions
   • Constraints
   • Confines
   • Architectural patterns
3. UML diagrams
   • Visually communicate structures and behaviors
   • Not constrained by a programming language

Deployment considerations

• Architecture drives production environment choices
• Production environment is the infrastructure that runs and delivers the software
  • Servers
  • Load balancers
  • Databases

Software Design and Modeling

Software Design:

Software design is a process to document:

• Structural components

• Behavioral attributes

  Models express software design using:

• Diagrams and flowcharts

• Unified Modeling Language (UML)

  Characteristics of structured design:

• Structural elements: modules & submodules
• Cohesive

• Loosely coupled

  Structure diagram example:

Behavioral models:

• Describe what a system does but doesn’t explain how it does it
• Communicate the behavior of the system
• Many types of behavioral UML diagrams
  • State transition
  • Interaction

Unified Modeling Language (UML):

• Visual representations to communicate architecture, design, and implementation
• Two types: structural and behavioral
• Programming language agnostic

Advantages of Unified Modeling Language (UML):

State transition diagram example:

Interaction diagram:

Object-Oriented Analysis and Design

Object-Oriented Languages:

• A patient could be an object
• An object contains data, and an object can perform actions

Classes and objects:

Object-Oriented analysis and design:

• Used for a system that can be modeled by interacting objects
• OOAD allows developers to work on different aspects of the same application at the same time
• Visual UML diagrams can be made to show both static structure and dynamic behavior of a system

Class diagram:

Software Architecture Patterns and Deployment Topologies

Approaches to Application Architecture

What is component?

• An individual unit of encapsulated functionality
• Serves as a part of an application in conjunction with other components

Component characteristics:

1. Reusable: reused in different applications
2. Replaceable: easily replaced with another component
3. Independent: doesn’t have dependencies on other components
4. Extensible: add behavior without changing other components
5. Encapsulated: doesn’t expose its specific implementation
6. Non-context specific: operates in different environments

Components examples:

Component-based architecture:

• Decomposes design into logical components
• Higher level abstraction than objects
• Defines, composes, and implements loosely coupled independent components, so they work together to create an application

Services

• Designed to be deployed independently and reused by multiple systems
• Solution to a business need
• Has one unique, always running instance with whom multiple clients communicate

Examples of Services:

• A service is a component that can be deployed independently
• Checking a customer’s credit
• Calculating a monthly loan payment
• Processing a mortgage application

Service-oriented architecture:

• Loosely coupled services that communicate over a network
• Supports building distributed systems that deliver services to other applications through the communication protocol

Distributed systems

• Multiple services located on different machines
• Services coordinate interactions via a communication protocol such as HTTP
• Appears to the end-user as a single coherent system

Distributed system characteristics:

• Shares resources
• Fault-tolerant
• Multiple activities run concurrently
• Scalable
• Runs on a variety of computers
• Programmed in a variety of languages

Nodes:

• Any devices on a network that can recognize, process, and transmit data to other nodes on the network
• Distributed systems have multiple interconnected nodes running services

Distributed system architectures:

Architectural Patterns in Software

Types of architectural patterns:

2-tier

3-tier

Peer-to-peer (P2P)

Event-driven

Microservices

Examples:

Combining patterns

Application Deployment Environments

Application environments:

Include:

• Application code/executables
• Software stack (libs, apps, middleware, OS)
• Networking infrastructure
• Hardware (compute, memory and storage)

Pre-production environments:

Production environment

• Entire solution stack ++
• Intended for all users
• Take load into consideration
• Other non-functional requirements
  • Security
  • Reliability
  • Scalability

• More complex than pre-production environments

  On-premises deployment:

• System and infrastructure reside in-house
• Offers greater control of the application
• Organization is responsible for everything
• Usually more expensive than compared to cloud deployment

Cloud deployment types:

Production Deployment Components

Production deployment infrastructure:

Web and application servers:

Proxy server:

• An intermediate server that handles requests between two tiers
• Can be used for load balancing, system optimization, caching, as a firewall, obscuring the source of a request, encrypting messages, scanning for malware, and more

• Can improve efficiency, privacy, and security

  Databases and database servers:

• Databases are a collection of related data stored on a computer that can be accessed in various ways
• DBMS (Database Management System) controls a database by connecting it to users or other programs
• Database servers control the flow and storage of data